Showing papers in "Applied Microbiology and Biotechnology in 2011"
TL;DR: The activity has been shown to be capable of killing a wide range of Gram-negative and Gram-positive bacteria, filamentous and unicellular fungi, algae, protozoa, mammalian viruses and bacteriophage, and the killing activity is enhanced by the presence of other antimicrobial agents such as Cu and Ag.
Abstract: The photocatalytic properties of titanium dioxide are well known and have many applications including the removal of organic contaminants and production of self-cleaning glass. There is an increasing interest in the application of the photocatalytic properties of TiO2 for disinfection of surfaces, air and water. Reviews of the applications of photocatalysis in disinfection (Gamage and Zhang 2010; Chong et al., Wat Res 44(10):2997–3027, 2010) and of modelling of TiO2 action have recently been published (Dalrymple et al. , Appl Catal B 98(1–2):27–38, 2010). In this review, we give an overview of the effects of photoactivated TiO2 on microorganisms. The activity has been shown to be capable of killing a wide range of Gram-negative and Gram-positive bacteria, filamentous and unicellular fungi, algae, protozoa, mammalian viruses and bacteriophage. Resting stages, particularly bacterial endospores, fungal spores and protozoan cysts, are generally more resistant than the vegetative forms, possibly due to the increased cell wall thickness. The killing mechanism involves degradation of the cell wall and cytoplasmic membrane due to the production of reactive oxygen species such as hydroxyl radicals and hydrogen peroxide. This initially leads to leakage of cellular contents then cell lysis and may be followed by complete mineralisation of the organism. Killing is most efficient when there is close contact between the organisms and the TiO2 catalyst. The killing activity is enhanced by the presence of other antimicrobial agents such as Cu and Ag.
891 citations
TL;DR: The chemical potential of endophytic fungi for drug discovery will be discussed with focus on the detection of pharmaceutically valuable plant constituents as products of fungal biosynthesis.
Abstract: Fungal endophytes residing in the internal tissues of living plants occur in almost every plant on earth from the arctic to the tropics. The endophyte–host relationship is described as a balanced symbiotic continuum ranging from mutualism through commensalism to parasitism. This overview will highlight selected aspects of endophyte diversity, host specificity, endophyte–host interaction and communication as well as regulation of secondary metabolite production with emphasis on advanced genomic methods and their role in improving our current knowledge of endophytic associations. Furthermore, the chemical potential of endophytic fungi for drug discovery will be discussed with focus on the detection of pharmaceutically valuable plant constituents as products of fungal biosynthesis. In addition, selected examples of bioactive metabolites reported in recent years (2008–2010) from fungal endophytes residing in terrestrial plants are presented grouped according to their reported biological activities.
526 citations
TL;DR: This mini-review will discuss the enzymes needed for complete degradation of plant polysaccharides and will give an overview of the latest developments concerning fungal carbohydrate-active enzymes and their corresponding families.
Abstract: Enzymatic degradation of plant polysaccharides has many industrial applications, such as within the paper, food, and feed industry and for sustainable production of fuels and chemicals. Cellulose, hemicelluloses, and pectins are the main components of plant cell wall polysaccharides. These polysaccharides are often tightly packed, contain many different sugar residues, and are branched with a diversity of structures. To enable efficient degradation of these polysaccharides, fungi produce an extensive set of carbohydrate-active enzymes. The variety of the enzyme set differs between fungi and often corresponds to the requirements of its habitat. Carbohydrate-active enzymes can be organized in different families based on the amino acid sequence of the structurally related catalytic modules. Fungal enzymes involved in plant polysaccharide degradation are assigned to at least 35 glycoside hydrolase families, three carbohydrate esterase families and six polysaccharide lyase families. This mini-review will discuss the enzymes needed for complete degradation of plant polysaccharides and will give an overview of the latest developments concerning fungal carbohydrate-active enzymes and their corresponding families.
515 citations
TL;DR: This mini-review briefly highlights and summarizes the results of studies during the past decade and especially in recent years, which concern the mechanism of action of different antimicrobial polymers and non-leaching microbicidal surfaces, and factors influencing their activity and toxicity, as well as major applications of antimicrobialpolymers.
Abstract: Complex epidemiological situation, nosocomial infections, microbial contamination, and infection risks in hospital and dental equipment have led to an ever-growing need for prevention of microbial infection in these various areas. Macromolecular systems, due to their properties, allow one to efficiently use them in various fields, including the creation of polymers with the antimicrobial activity. In the past decade, the intensive development of a large class of antimicrobial macromolecular systems, polymers, and copolymers, either quaternized or functionalized with bioactive groups, has been continued, and they have been successfully used as biocides. Various permanent microbicidal surfaces with non-leaching polymer antimicrobial coatings have been designed. Along with these trends, new moderately hydrophobic polymer structures have been synthesized and studied, which contain protonated primary or secondary/tertiary amine groups that exhibited rather high antimicrobial activity, often unlike their quaternary analogues. This mini-review briefly highlights and summarizes the results of studies during the past decade and especially in recent years, which concern the mechanism of action of different antimicrobial polymers and non-leaching microbicidal surfaces, and factors influencing their activity and toxicity, as well as major applications of antimicrobial polymers.
508 citations
TL;DR: Yeast do exhibit advantages for lipid production over other microbial sources, namely, their duplication times are usually lower than 1 h, are much less affected than plants by season or climate conditions, and their cultures are more easily scaled up than those of microalgae.
Abstract: Oily yeasts have been described to be able to accumulate lipids up to 20% of their cellular dry weight. These yeasts represent a minor proportion of the total yeast population, and only 5% of them have been reported as able to accumulate more than 25% of lipids. The oily yeast genera include Yarrowia, Candida, Rhodotorula, Rhodosporidium, Cryptococcus, Trichosporon, and Lipomyces. More specifically, examples of oleaginous yeasts include the species: Lipomyces starkeyi, Rhodosporidium toruloides, Rhodotorula glutinis, and Yarrowia lipolytica. Yeast do exhibit advantages for lipid production over other microbial sources, namely, their duplication times are usually lower than 1 h, are much less affected than plants by season or climate conditions, and their cultures are more easily scaled up than those of microalgae. Additionally, some oily yeasts have been reported to accumulate oil up to 80% of their dry weight and can indeed generate different lipids from different carbon sources or from lipids present in the culture media. Thus, they can vary their lipid composition by replacing the fatty acids present in their triglycerides. Due to the diversity of microorganisms and growth conditions, oily yeasts can be useful for the production of triglycerides, surfactants, or polyunsaturated fatty acids.
496 citations
TL;DR: Combined higher salinity and light intensity was detrimental to lipid productivity under nitrogen starvation; biomass TFA content, and lipid productivity amounted for only 33% of DW and ca.
Abstract: We examined responses of batch cultures of the marine microalga Nannochloropsis sp. to combined alterations in salinity (13, 27, and 40 g/l NaCl) and light intensity (170 and 700 μmol photons/m2·s). Major growth parameters and lipid productivity (based on total fatty acid determination) were determined in nitrogen-replete and nitrogen-depleted cultures of an initial biomass of 0.8 and 1.4 g/l, respectively. On the nitrogen-replete medium, increases in light intensity and salinity increased the cellular content of dry weight and lipids due to enhanced formation of triacylglycerols (TAG). Maximum average productivity of ca. 410 mg TFA/l/d were obtained at 700 μmol photons/m2·s and 40 g/l NaCl within 7 days. Under stressful conditions, content of the major LC-PUFA, eicosapentaenoic acid (EPA), was significantly reduced while TAG reached 25% of biomass. In contrast, lower salinity tended to improve major growth parameters, consistent with less variation in EPA contents. Combined higher salinity and light intensity was detrimental to lipid productivity under nitrogen starvation; biomass TFA content, and lipid productivity amounted for only 33% of DW and ca. 200 mg TFA/l/day, respectively. The highest biomass TFA content (ca. 47% DW) and average lipid productivity of ca. 360 mg TFA/l/day were achieved at 13 g/l NaCl and 700 μmol photons/m2·s. Our data further support selecting Nannochloropsis as promising microalgae for biodiesel production. Moreover, appropriate cultivation regimes may render Nannochloropsis microalgae to produce simultaneously major valuable components, EPA, and TAG, while sustaining relatively high biomass growth rates.
495 citations
TL;DR: The nature of light is introduced, and its harvesting and transformation by microalgae is described, as well as its metabolic effects under excessively low or high supply.
Abstract: In order to enhance microalgal growth in photobioreactors (PBRs), light requirement is one of the most important parameters to be addressed; light should indeed be provided at the appropriate intensity, duration, and wavelength. Excessive intensity may lead to photo-oxidation and -inhibition, whereas low light levels will become growth-limiting. The constraint of light saturation may be overcome via either of two approaches: increasing photosynthetic efficiency by genetic engineering, aimed at changing the chlorophyll antenna size; or increasing flux tolerance, via tailoring the photonic spectrum, coupled with its intensity and temporal characteristics. These approaches will allow an increased control over the illumination features, leading to maximization of microalgal biomass and metabolite productivity. This minireview briefly introduces the nature of light, and describes its harvesting and transformation by microalgae, as well as its metabolic effects under excessively low or high supply. Optimization of the photosynthetic efficiency is discussed under the two approaches referred to above; the selection of light sources, coupled with recent improvements in light handling by PBRs, are chronologically reviewed and critically compared.
438 citations
TL;DR: Known gyrase-specific drugs and toxins are reviewed and the prospects for developing new antibacterials targeted to this enzyme are assessed.
Abstract: DNA gyrase is a type II topoisomerase that can introduce negative supercoils into DNA at the expense of ATP hydrolysis. It is essential in all bacteria but absent from higher eukaryotes, making it an attractive target for antibacterials. The fluoroquinolones are examples of very successful gyrase-targeted drugs, but the rise in bacterial resistance to these agents means that we not only need to seek new compounds, but also new modes of inhibition of this enzyme. We review known gyrase-specific drugs and toxins and assess the prospects for developing new antibacterials targeted to this enzyme.
434 citations
TL;DR: The current state of understanding of bacterial cellulose, known methods for controlling its physical and chemical structure, biomedical applications for which it is currently being used, or investigated for use, challenges yet to be overcome, and future possibilities for BC are reviewed.
Abstract: Bacterial cellulose (BC) is a unique and promising material for use as implants and scaffolds in tissue engineering. It is composed of a pure cellulose nanofiber mesh spun by bacteria. It is remarkable for its strength and its ability to be engineered structurally and chemically at nano-, micro-, and macroscales. Its high water content and purity make the material biocompatible for multiple medical applications. Its biocompatibility, mechanical strength, chemical and morphologic controllability make it a natural choice for use in the body in biomedical devices with broader application than has yet been utilized. This paper reviews the current state of understanding of bacterial cellulose, known methods for controlling its physical and chemical structure (e.g., porosity, fiber alignment, etc.), biomedical applications for which it is currently being used, or investigated for use, challenges yet to be overcome, and future possibilities for BC.
432 citations
TL;DR: Another advantage derives from the possibility to co-immobilize two or more enzymes to provide CLEAs that are capable of catalyzing multiple biotransformations, independently or in sequence as catalytic cascade processes.
Abstract: Cross-linked enzyme aggregates (CLEAs) have many economic and environmental benefits in the context of industrial biocatalysis. They are easily prepared from crude enzyme extracts, and the costs of (often expensive) carriers are circumvented. They generally exhibit improved storage and operational stability towards denaturation by heat, organic solvents, and autoproteolysis and are stable towards leaching in aqueous media. Furthermore, they have high catalyst productivities (kilograms product per kilogram biocatalyst) and are easy to recover and recycle. Yet another advantage derives from the possibility to co-immobilize two or more enzymes to provide CLEAs that are capable of catalyzing multiple biotransformations, independently or in sequence as catalytic cascade processes.
412 citations
TL;DR: This review discusses the various mechanisms provided for the biological synthesis of metal nanoparticles by peptides, bacteria, fungi, and plants and concludes that the mechanistic aspects in some of the biological systems need more detailed studies.
Abstract: Metal nanoparticles have been studied and applied in many areas including the biomedical, agricultural, electronic fields, etc. Several products of colloidal silver are already on the market. Research on new, eco-friendly and cheaper methods has been initiated. Biological production of metal nanoparticles has been studied by many researchers due to the convenience of the method that produces small particles stabilized by protein. However, the mechanism involved in this production has not yet been elucidated although hypothetical mechanisms have been proposed in the literature. Thus, this review discusses the various mechanisms provided for the biological synthesis of metal nanoparticles by peptides, bacteria, fungi, and plants. One thing that is clear is that the mechanistic aspects in some of the biological systems need more detailed studies.
TL;DR: Several of the mushroom polysaccharide compounds have proceeded through phases I, II, and III clinical trials and are used extensively and successfully in Asia to treat various cancers and other diseases.
Abstract: The target of the present review is to draw attention to many critically important unsolved problems in the future development of medicinal mushroom science in the twenty-first century. Special attention is paid to mushroom polysaccharides. Many, if not all, higher Basidiomycetes mushrooms contain biologically active polysaccharides in fruit bodies, cultured mycelium, and cultured broth. The data on mushroom polysaccharides are summarized for approximately 700 species of higher Hetero- and Homobasidiomycetes. The chemical structure of polysaccharides and its connection to antitumor activity, including possible ways of chemical modification, experimental testing and clinical use of antitumor or immunostimulating polysaccharides, and possible mechanisms of their biological action, are discussed. Numerous bioactive polysaccharides or polysaccharide–protein complexes from medicinal mushrooms are described that appear to enhance innate and cell-mediated immune responses and exhibit antitumor activities in animals and humans. Stimulation of host immune defense systems by bioactive polymers from medicinal mushrooms has significant effects on the maturation, differentiation, and proliferation of many kinds of immune cells in the host. Many of these mushroom polymers were reported previously to have immunotherapeutic properties by facilitating growth inhibition and destruction of tumor cells. While the mechanism of their antitumor actions is still not completely understood, stimulation and modulation of key host immune responses by these mushroom polymers appears central. Particularly and most importantly for modern medicine are polysaccharides with antitumor and immunostimulating properties. Several of the mushroom polysaccharide compounds have proceeded through phases I, II, and III clinical trials and are used extensively and successfully in Asia to treat various cancers and other diseases. A total of 126 medicinal functions are thought to be produced by medicinal mushrooms and fungi including antitumor, immunomodulating, antioxidant, radical scavenging, cardiovascular, antihypercholesterolemia, antiviral, antibacterial, antiparasitic, antifungal, detoxification, hepatoprotective, and antidiabetic effects.
TL;DR: Results show that inoculation and enrichment procedures are critical to the initial success of larger-scale systems and better methods will be needed to isolate hydrogen gas produced at the cathode.
Abstract: A pilot-scale (1,000 L) continuous flow microbial electrolysis cell was constructed and tested for current generation and COD removal with winery wastewater. The reactor contained 144 electrode pairs in 24 modules. Enrichment of an exoelectrogenic biofilm required ~60 days, which is longer than typically needed for laboratory reactors. Current generation was enhanced by ensuring adequate organic volatile fatty acid content (VFA/SCOD ≥ 0.5) and by raising the wastewater temperature (31 ± 1°C). Once enriched, SCOD removal (62 ± 20%) was consistent at a hydraulic retention time of 1 day (applied voltage of 0.9 V). Current generation reached a maximum of 7.4 A/m3 by the planned end of the test (after 100 days). Gas production reached a maximum of 0.19 ± 0.04 L/L/day, although most of the product gas was converted to methane (86 ± 6%). In order to increase hydrogen recovery in future tests, better methods will be needed to isolate hydrogen gas produced at the cathode. These results show that inoculation and enrichment procedures are critical to the initial success of larger-scale systems. Acetate amendments, warmer temperatures, and pH control during startup were found to be critical for proper enrichment of exoelectrogenic biofilms and improved reactor performance.
TL;DR: New findings in the isolation methods, bio- and chemical diversity of endophytic actinobacteria are focused on and the potential biotechnological application is revealed.
Abstract: Endophytic actinobacteria, which exist in the inner tissues of living plants, have attracted increasing attention among taxonomists, ecologists, agronomists, chemists and evolutionary biologists. Numerous studies have indicated that these prolific actinobacteria appear to have a capacity to produce an impressive array of secondary metabolites exhibiting a wide variety of biological activity, such as antibiotics, antitumor and anti-infection agents, plant growth promoters and enzymes, and may contribute to their host plants by promoting growth and enhancing their ability of withstanding the environmental stresses. These microorganisms may represent an underexplored reservoir of novel species of potential interest in the discovery of novel lead compounds and for exploitation in pharmaceutical, agriculture and industry. This review focuses on new findings in the isolation methods, bio- and chemical diversity of endophytic actinobacteria and reveals the potential biotechnological application. The facing problems and strategies for biodiversity research and bioactive natural products producing are also discussed.
TL;DR: An overview ofpullulan’s chemistry, biosynthesis, applications, state-of-the-art advances in the enhancement of pullulan production through the investigations of enzyme regulations, molecular properties, cultivation parameters, and bioreactor design is presented.
Abstract: Pullulan is a linear glucosic polysaccharide produced by the polymorphic fungus Aureobasidium pullulans, which has long been applied for various applications from food additives to environmental remediation agents. This review article presents an overview of pullulan’s chemistry, biosynthesis, applications, state-of-the-art advances in the enhancement of pullulan production through the investigations of enzyme regulations, molecular properties, cultivation parameters, and bioreactor design. The enzyme regulations are intended to illustrate the influences of metabolic pathway on pullulan production and its structural composition. Molecular properties, such as molecular weight distribution and pure pullulan content, of pullulan are crucial for pullulan applications and vary with different fermentation parameters. Studies on the effects of environmental parameters and new bioreactor design for enhancing pullulan production are getting attention. Finally, the potential applications of pullulan through chemical modification as a novel biologically active derivative are also discussed.
TL;DR: This review focuses on the ongoing research on different oleaginous yeasts producing high added value lipids and on the prospects of such microbial oils to be used in different biotechnological processes and applications.
Abstract: High energy prices, depletion of crude oil supplies, and price imbalance created by the increasing demand of plant oils or animal fat for biodiesel and specific lipid derivatives such as lubricants, adhesives, and plastics have given rise to heated debates on land-use practices and to environmental concerns about oil production strategies. However, commercialization of microbial oils with similar composition and energy value to plant and animal oils could have many advantages, such as being non-competitive with food, having shorter process cycle and being independent of season and climate factors. This review focuses on the ongoing research on different oleaginous yeasts producing high added value lipids and on the prospects of such microbial oils to be used in different biotechnological processes and applications. It covers the basic biochemical mechanisms of lipid synthesis and accumulation in these organisms, along with the latest insights on the metabolic processes involved. The key elements of lipid accumulation, the mechanisms suspected to confer the oleaginous character of the cell, and the potential metabolic routes enhancing lipid production are also extensively discussed.
TL;DR: The major important biochemical pathways in cyanobacteria are highlighted, and the possibility to influence these pathways to improve the production of specific types of energy forms the major part of this review.
Abstract: The need to develop and improve sustainable energy resources is of eminent importance due to the finite nature of our fossil fuels. This review paper deals with a third generation renewable energy resource which does not compete with our food resources, cyanobacteria. We discuss the current state of the art in developing different types of bioenergy (ethanol, biodiesel, hydrogen, etc.) from cyanobacteria. The major important biochemical pathways in cyanobacteria are highlighted, and the possibility to influence these pathways to improve the production of specific types of energy forms the major part of this review.
TL;DR: This review provides special emphasis on the selection of new yeast strains, genetic breeding, and recombinant DNA technology, as applied to bioethanol production processes, as applications in Brazil.
Abstract: Bioethanol (fuel alcohol) has been produced by industrial alcoholic fermentation processes in Brazil since the beginning of the twentieth century. Currently, 432 mills and distilleries crush about 625 million tons of sugarcane per crop, producing about 27 billion liters of ethanol and 38.7 million tons of sugar. The production of bioethanol from sugarcane represents a major large-scale technology capable of producing biofuel efficiently and economically, providing viable substitutes to gasoline. The combination of immobilization of CO2 by sugarcane crops by photosynthesis into biomass together with alcoholic fermentation of this biomass has allowed production of a clean and high-quality liquid fuel that contains 93% of the original energy found in sugar. Over the last 30 years, several innovations have been introduced to Brazilian alcohol distilleries resulting in the improvement of plant efficiency and economic competitiveness. Currently, the main scientific challenges are to develop new technologies for bioethanol production from first and second generation feedstocks that exhibit positive energy balances and appropriately meet environmental sustainability criteria. This review focuses on these aspects and provides special emphasis on the selection of new yeast strains, genetic breeding, and recombinant DNA technology, as applied to bioethanol production processes.
TL;DR: In this paper, Nannochloropsis oculata CCMP 525, Dunaliella salina FACHB 435, and Chlorella sorokiniana CCTCC M209220 were compared in mixotrophic and photoautotrophic cultures in terms of growth rate, protein, and lipid content.
Abstract: Nannochloropsis oculata CCMP 525, Dunaliella salina FACHB 435, and Chlorella sorokiniana CCTCC M209220 were compared in mixotrophic and photoautotrophic cultures in terms of growth rate, protein, and lipid content. Growth improved in glucose, and the biomass productivities of N. oculata, D. salina, and C. sorokiniana were found to be 1.4-, 2.2- and 4.2-fold that observed photoautotrophically. However, biomass and lipid production decreased at the highest glucose concentrations. Meanwhile, the content of protein and lipid were significantly augmented for mixotrophic conditions at least for some species. C. sorokiniana was found to be well suited for lipid production based on its high biomass production rate and lipid content reaching 51% during mixotrophy. Expression levels of accD (heteromeric acetyl-CoA carboxylase beta subunit), acc1 (homomeric acetyl-CoA carboxylase), rbcL (ribulose 1, 5-bisphosphate carboxylase/oxygenase large subunit) genes in C. sorokiniana were studied by real-time PCR. Increased expression levels of accD reflect the increased lipid content in stationary phase of mixotrophic growth, but expression of the acc1 gene remains low, suggesting that this gene may not be critical to lipid accumulation. Additionally, reduction of expression of the rbcL gene during mixotrophy indicated that utilization of glucose was found to reduce the role of this gene and photosynthesis.
TL;DR: The diversity of sulfate reducers associated with oil reservoirs, approaches for determining their presence and effects, the factors that control souring, and the approaches (along with the current understanding of their underlying mechanisms) that may be used to successfully mitigate souring in low-temperature and high-tem temperature oilfield operations are reported.
Abstract: Souring in oilfield systems is most commonly due to the action of sulfate-reducing prokaryotes, a diverse group of anaerobic microorganisms that respire sulfate and produce sulfide (the key souring agent) while oxidizing diverse electron donors. Such biological sulfide production is a detrimental, widespread phenomenon in the petroleum industry, occurring within oil reservoirs or in topside processing facilities, under low- and high-temperature conditions, and in onshore or offshore operations. Sulfate reducers can exist either indigenously in deep subsurface reservoirs or can be “inoculated” into a reservoir system during oilfield development (e.g., via drilling operations) or during the oil production phase. In the latter, souring most commonly occurs during water flooding, a secondary recovery strategy wherein water is injected to re-pressurize the reservoir and sweep the oil towards production wells to extend the production life of an oilfield. The water source and type of production operation can provide multiple components such as sulfate, labile carbon sources, and sulfate-reducing communities that influence whether oilfield souring occurs. Souring can be controlled by biocides, which can non-specifically suppress microbial populations, and by the addition of nitrate (and/or nitrite) that directly impacts the sulfate-reducing population by numerous competitive or inhibitory mechanisms. In this review, we report on the diversity of sulfate reducers associated with oil reservoirs, approaches for determining their presence and effects, the factors that control souring, and the approaches (along with the current understanding of their underlying mechanisms) that may be used to successfully mitigate souring in low-temperature and high-temperature oilfield operations.
TL;DR: It is confirmed that, although fundamental knowledge is now available, the development of efficient, economically feasible large-scale bioprocesses remains an obstacle to the commercialisation of this promising technology.
Abstract: Microalgae of numerous heterotrophic genera (obligate or facultative) exhibit considerable metabolic versatility and flexibility but are currently underexploited in the biotechnological manufacturing of known plant-derived compounds, novel high-value biomolecules or enriched biomass. Highly efficient production of microalgal biomass without the need for light is now feasible in inexpensive, well-defined mineral medium, typically supplemented with glucose. Cell densities of more than 100 g l−1 cell dry weight have been achieved with Chlorella, Crypthecodinium and Galdieria species while controlling the addition of organic sources of carbon and energy in fedbatch mode. The ability of microalgae to adapt their metabolism to varying culture conditions provides opportunities to modify, control and thereby maximise the formation of targeted compounds with non-recombinant microalgae. This review outlines the critical aspects of cultivation technology and current best practices in the heterotrophic high-cell-density cultivation of microalgae. The primary topics include (1) the characteristics of microalgae that make them suitable for heterotrophic cultivation, (2) the appropriate chemical composition of mineral growth media, (3) the different strategies for fedbatch cultivations and (4) the principles behind the customisation of biomass composition. The review confirms that, although fundamental knowledge is now available, the development of efficient, economically feasible large-scale bioprocesses remains an obstacle to the commercialisation of this promising technology.
TL;DR: Lectins manifest a diversity of activities including antitumor, immunomodulatory, antifungal, HIV-1 reverse transcriptase inhibitory, and anti-insect activities, which may find practical applications.
Abstract: Lectins are proteins found in a diversity of organisms. They possess the ability to agglutinate erythrocytes with known carbohydrate specificity since they have at least one non-catalytic domain that binds reversibly to specific monosaccharides or oligosaccharides. This articles aims to review the production and practical applications of lectins. Lectins are isolated from their natural sources by chromatographic procedures or produced by recombinant DNA technology. The yields of animal lectins are usually low compared with the yields of plant lectins such as legume lectins. Lectins manifest a diversity of activities including antitumor, immunomodulatory, antifungal, HIV-1 reverse transcriptase inhibitory, and anti-insect activities, which may find practical applications. A small number of lectins demonstrate antibacterial and anti-nematode activities.
TL;DR: The few attempts done in the use of EPS-producing cyanobacteria for metal biosorption at pilot scale and with real wastewaters are reviewed, discussing the main positive issues and the drawbacks so far emerging from these experiments.
Abstract: Microorganisms can remove metals from the surrounding environment with various mechanisms, either as metabolically mediated processes or as a passive adsorption of metals on the charged macromolecules of the cell envelope. Owing to the presence of a large number of negative charges on the external cell layers, exopolysaccharides (EPS)-producing cyanobacteria have been considered very promising as chelating agents for the removal of positively charged heavy metal ions from water solutions, and an increasing number of studies on their use in metal biosorption have been published in recent years. In this review, the attention was mainly focused on the studies aimed at defining the molecular mechanisms of the metal binding to the polysaccharidic exocellular layers. Moreover, the few attempts done in the use of EPS-producing cyanobacteria for metal biosorption at pilot scale and with real wastewaters are here reviewed, discussing the main positive issues and the drawbacks so far emerging from these experiments.
TL;DR: In this review, some of the most important findings regarding the interactions between AM fungi and soil bacteria with some new insights for future research are presented.
Abstract: The soil environment is interesting and complicated. There are so many interactions taking place in the soil, which determine the properties of soil as a medium for the growth and activities of plants and soil microorganisms. The soil fungi, arbuscular mycorrhiza (AM), are in mutual and beneficial symbiosis with most of the terrestrial plants. AM fungi are continuously interactive with a wide range of soil microorganisms including nonbacterial soil microorganisms, plant growth promoting rhizobacteria, mycorrhiza helper bacteria and deleterious bacteria. Their interactions can have important implications in agriculture. There are some interesting interactions between the AM fungi and soil bacteria including the binding of soil bacteria to the fungal spore, the injection of molecules by bacteria into the fungal spore, the production of volatiles by bacteria and the degradation of fungal cellular wall. Such mechanisms can affect the expression of genes in AM fungi and hence their performance and ecosystem productivity. Hence, consideration of such interactive behavior is of significance. In this review, some of the most important findings regarding the interactions between AM fungi and soil bacteria with some new insights for future research are presented.
TL;DR: Improved understanding of yeast tolerance and in situ detoxification provide insight into phenotype-genotype relationships, dissection of tolerance mechanisms, and strategies for more tolerant strain development for biofuels applications.
Abstract: Pretreatment of lignocellulose biomass for biofuel production generates inhibitory compounds that interfere with microbial growth and subsequent fermentation. Remediation of the inhibitors by current physical, chemical, and biological abatement means is economically impractical, and overcoming the inhibitory effects of lignocellulose hydrolysate poses a significant technical challenge for lower-cost cellulosic ethanol production. Development of tolerant ethanologenic yeast strains has demonstrated the potential of in situ detoxification for numerous aldehyde inhibitors derived from lignocellulose biomass pretreatment and conversion. In the last decade, significant progress has been made in understanding mechanisms of yeast tolerance for tolerant strain development. Enriched genetic backgrounds, enhanced expression, interplays, and global integration of many key genes enable yeast tolerance. Reprogrammed pathways support yeast functions to withstand the inhibitor stress, detoxify the toxic compounds, maintain energy and redox balance, and complete active metabolism for ethanol fermentation. Complex gene interactions and regulatory networks as well as co-regulation are well recognized as involved in yeast adaptation and tolerance. This review presents our current knowledge on mechanisms of the inhibitor detoxification based on molecular studies and genomic-based approaches. Our improved understanding of yeast tolerance and in situ detoxification provide insight into phenotype-genotype relationships, dissection of tolerance mechanisms, and strategies for more tolerant strain development for biofuels applications.
TL;DR: This work summarizes some of the recent metabolic engineering strategies in plants and microorganisms, with a focus on applications of metabolic flux analysis and is confident that these engineering approaches will lead to successful industrial flavonoid production in the near future.
Abstract: Over 9,000 flavonoid compounds have been found in various plants, comprising one of the largest families of natural products. Flavonoids are an essential factor in plant interactions with the environment, often serving as the first line of defense against UV irradiation and pathogen attacks. Flavonoids are also major nutritional compounds in foods and beverages, with demonstrated health benefits. Some flavonoids are potent antioxidants, and specific flavonoid compounds are beneficial in many physiological and pharmacological processes. Therefore, engineering of flavonoid biosynthesis in plants or in microorganisms has significant scientific and economical importance. Construction of biosynthetic pathways in heterologous systems offers promising results for large-scale flavonoid production by fermentation or bioconversion. Genomics and metabolomics now offer unprecedented tools for detailed understanding of the engineered transgenic organism and for developing novel technologies to further increase flavonoid production yields. We summarize some of the recent metabolic engineering strategies in plants and microorganisms, with a focus on applications of metabolic flux analysis. We are confident that these engineering approaches will lead to successful industrial flavonoid production in the near future.
TL;DR: This review emphasizes the potential of P. rhodozyma for the biotechnological production of astaxanthin in comparison to other natural sources such as the microalga H. pluvialis, other fungi and transgenic plants and to chemical synthesis.
Abstract: The oxygenated β-carotene derivative astaxanthin exhibits outstanding colouring, antioxidative and health-promoting properties and is mainly found in the marine environment. To satisfy the growing demand for this ketocarotenoid in the feed, food and cosmetics industries, there are strong efforts to develop economically viable bioprocesses alternative to the current chemical synthesis. However, up to now, natural astaxanthin from Haematococcus pluvialis, Phaffia rhodozyma or Paracoccus carotinifaciens has not been cost competitive with chemically synthesized astaxanthin, thus only serving niche applications. This review illuminates recent advances made in elucidating astaxanthin biosynthesis in P. rhodozyma. It intensely focuses on strategies to increase astaxanthin titers in the heterobasidiomycetous yeast by genetic engineering of the astaxanthin pathway, random mutagenesis and optimization of fermentation processes. This review emphasizes the potential of P. rhodozyma for the biotechnological production of astaxanthin in comparison to other natural sources such as the microalga H. pluvialis, other fungi and transgenic plants and to chemical synthesis.
TL;DR: The translation of the isobutanol process from shake flasks to a 1-L bioreactor in order to characterize three E. coli strains suggests that in situ product removal can properly overcome isOButanol toxicity in E. Escherichia coli cultures.
Abstract: Promising approaches to produce higher alcohols, e.g., isobutanol, using Escherichia coli have been developed with successful results. Here, we translated the isobutanol process from shake flasks to a 1-L bioreactor in order to characterize three E. coli strains. With in situ isobutanol removal from the bioreactor using gas stripping, the engineered E. coli strain (JCL260) produced more than 50 g/L in 72 h. In addition, the isobutanol production by the parental strain (JCL16) and the high isobutanol-tolerant mutant (SA481) were compared with JCL260. Interestingly, we found that the isobutanol-tolerant strain in fact produced worse than either JCL16 or JCL260. This result suggests that in situ product removal can properly overcome isobutanol toxicity in E. coli cultures. The isobutanol productivity was approximately twofold and the titer was 9% higher than n-butanol produced by Clostridium in a similar integrated system.
TL;DR: Fungal acetyltransferases and plant glucosyl transferases targeting carbon 3 of trichothecenes remain promising candidates for engineering resistance against Fusarium head blight.
Abstract: Deoxynivalenol (DON) is the major mycotoxin produced by Fusarium fungi in grains. Food and feed contaminated with DON pose a health risk to humans and livestock. The risk can be reduced by enzymatic detoxification. Complete mineralization of DON by microbial cultures has rarely been observed and the activities turned out to be unstable. The detoxification of DON by reactions targeting its epoxide group or hydroxyl on carbon 3 is more feasible. Microbial strains that de-epoxidize DON under anaerobic conditions have been isolated from animal digestive system. Feed additives claimed to de-epoxidize trichothecenes enzymatically are on the market but their efficacy has been disputed. A new detoxification pathway leading to 3-oxo-DON and 3-epi-DON was discovered in taxonomically unrelated soil bacteria from three continents; the enzymes involved remain to be identified. Arabidopsis, tobacco, wheat, barley, and rice were engineered to acetylate DON on carbon 3. In wheat expressing DON acetylation activity, the increase in resistance against Fusarium head blight was only moderate. The Tri101 gene from Fusarium sporotrichioides was used; Fusarium graminearum enzyme which possesses higher activity towards DON would presumably be a better choice. Glycosylation of trichothecenes occurs in plants, contributing to the resistance of wheat to F. graminearum infection. Marker-assisted selection based on the trichothecene-3-O-glucosyltransferase gene can be used in breeding for resistance. Fungal acetyltransferases and plant glucosyltransferases targeting carbon 3 of trichothecenes remain promising candidates for engineering resistance against Fusarium head blight. Bacterial enzymes catalyzing oxidation, epimerization, and less likely de-epoxidation of DON may extend this list in future.
TL;DR: This review aims to discuss PAH degradation under various redox potential conditions, the factors affecting the biodegradation rates, degrading bacteria, the relevant genes in molecular monitoring methods, and some recent-year bioremediation field studies.
Abstract: Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in the natural environment and easily accumulate in soil and sediment due to their low solubility and high hydrophobicity, rendering them less available for biological degradation. However, microbial degradation is a promising mechanism which is responsible for the ecological recovery of PAH-contaminated soil and sediment for removing these recalcitrant compounds compared with chemical degradation of PAHs. The goal of this review is to provide an outline of the current knowledge of biodegradation of PAHs in related aspects. Over 102 publications related to PAH biodegradation in soil and sediment are compiled, discussed, and analyzed. This review aims to discuss PAH degradation under various redox potential conditions, the factors affecting the biodegradation rates, degrading bacteria, the relevant genes in molecular monitoring methods, and some recent-year bioremediation field studies. The comprehensive understanding of the bioremediation kinetics and molecular means will be helpful for optimizing and monitoring the process, and overcoming its limitations in practical projects.