Showing papers in "Applied Microbiology and Biotechnology in 1998"
TL;DR: It is suggested that the SBR could be used for the enrichment and quantitative study of a large number of slowly growing microorganisms that are currently out of reach for microbiological research.
Abstract: Currently available microbiological techniques are not designed to deal with very slowly growing microorganisms. The enrichment and study of such organisms demands a novel experimental approach. In the present investigation, the sequencing batch reactor (SBR) was applied and optimized for the enrichment and quantitative study of a very slowly growing microbial community which oxidizes ammonium anaerobically. The SBR was shown to be a powerful experimental set-up with the following strong points: (1) efficient biomass retention, (2) a homogeneous distribution of substrates, products and biomass aggregates over the reactor, (3) reliable operation for more than 1 year, and (4) stable conditions under substrate-limiting conditions. Together, these points made possible for the first time the determination of several important physiological parameters such as the biomass yield (0.066 ± 0.01 C-mol/mol ammonium), the maximum specific ammonium consumption rate (45 ± 5 nmol/mg protein/min) and the maximum specific growth rate (0.0027 · h−1, doubling time 11 days). In addition, the persisting stable and strongly selective conditions of the SBR led to a high degree of enrichment (74% of the desired microorganism). This study has demonstrated that the SBR is a powerful tool compared to other techniques used in the past. We suggest that the SBR could be used for the enrichment and quantitative study of a large number of slowly growing microorganisms that are currently out of reach for microbiological research.
2,022 citations
TL;DR: A novel method to increase the fermentability of lignocellulosic hydrolysates: enzymatic detoxification, which indicates that the mechanism of laccase detoxification involves removal of monoaromatic phenolic compounds present in the hydrolysate, and supports the suggestion that phenolics are important inhibitors of the fermentation process.
Abstract: Fermentation of wood hydrolysates to desirable products, such as fuel ethanol, is made difficult by the presence of inhibitory compounds in the hydrolysates. Here we present a novel method to increase the fermentability of lignocellulosic hydrolysates: enzymatic detoxification. Besides the detoxification effect, treatment with purified enzymes provides a new way to identify inhibitors by assaying the effect of enzymatic attack on specific compounds in the hydrolysate. Laccase, a phenol oxidase, and lignin peroxidase purified from the ligninolytic basidiomycete fungus Trametes versicolor were studied using a lignocellulosic hydrolysate from willow pretreated with steam and SO2. Saccharomyces cerevisiae was employed for ethanolic fermentation of the hydrolysates. The results show more rapid consumption of glucose and increased ethanol productivity for samples treated with laccase. Treatment of the hydrolysate with lignin peroxidase also resulted in improved fermentability. Analyses by GC-MS indicated that the mechanism of laccase detoxification involves removal of monoaromatic phenolic compounds present in the hydrolysate. The results support the suggestion that phenolic compounds are important inhibitors of the fermentation process.
442 citations
TL;DR: A reintroduction of acetone/butanol fermentation on an industrial scale seems to be economically feasible, a view that is supported by a new pilot plant in Austria recently coming into operation.
Abstract: Clostridial acetone/butanol fermentation used to rank second only to ethanol fermentation by yeast in its scale of production and thus is one of the largest biotechnological processes known Its decline since about 1950 has been caused by increasing substrate costs and the availability of much cheaper feedstocks for chemical solvent synthesis by the petrochemical industry The so-called oil crisis in 1973 led to renewed interest in novel fermentation and product recovery technologies as well as in the metabolism and genetics of the bacterial species involved As a consequence, almost all of the enzymes leading to solvent formation are known, their genes have been sequenced (in fact, Clostridium acetobutylicum has been recently included in the microbial genome sequencing project), the regulatory mechanisms controlling solventogenesis have begun to emerge and recombinant DNA techniques have been developed for these clostridia to construct specific production strains In parallel, cheap agricultural-waste-based feedstocks have been exploited for their potential as novel substrates, continuous culture methods have been successfully established and new on-line product recovery technologies are now available, such as gas stripping, liquid/liquid extraction, and membrane-based methods In combination with these achievements, a reintroduction of acetone/butanol fermentation on an industrial scale seems to be economically feasible, a view that is supported by a new pilot plant in Austria recently coming into operation
406 citations
TL;DR: The perspectives of bioprocesses for the oxifunctionalisation of lower terpenes by genetically modified organisms and economic aspects are discussed.
Abstract: The biotechnological generation of natural aroma compounds is rapidly expanding. Aroma chemicals, such as vanillin, benzaldehyde (bitter almond, cherry) and 4-(R)-decanolide (fruity-fatty) are marketed on a scale of several thousand tons per year. Their possible production by single-step biotransformations, bioconversions and de novo synthesis using microorganisms, plant cells or isolated enzymes is shown. The perspectives of bioprocesses for the oxifunctionalisation of lower terpenes by genetically modified organisms and economic aspects are discussed.
390 citations
TL;DR: Xanthan gum is a complex exopolysaccharide produced by the plant-pathogenic bacterium Xanthomonas campestris pv. as mentioned in this paper, which is widely used as a thickener or viscosifier in both food and non-food industries.
Abstract: Xanthan gum is a complex exopolysaccharide produced by the plant-pathogenic bacterium Xanthomonas campestris pv. campestris. It consists of D-glucosyl, D-mannosyl, and D-glucuronyl acid residues in a molar ratio of 2:2:1 and variable proportions of O-acetyl and pyruvyl residues. Because of its physical properties, it is widely used as a thickener or viscosifier in both food and non-food industries. Xanthan gum is also used as a stabilizer for a wide variety of suspensions, emulsions, and foams. This article outlines aspects of the biochemical assembly and genetic loci involved in its biosynthesis, including the synthesis of the sugar nucleotide substrates, the building and decoration of the pentasaccharide subunit, and the polymerization and secretion of the polymer. An overview of the applications and industrial production of xanthan is also covered.
375 citations
TL;DR: In this paper, a review of the bacterial degradation of pyridine and its derivatives, indole, isoquinoline, and quinoline and their derivatives is presented, and the bacterial metabolism of these compounds under different redox conditions is discussed.
Abstract: Bacteria have evolved a diverse potential to transform and even mineralize numerous organic compounds of both natural and xenobiotic origin. This article describes the occurrence of N-heteroaromatic compounds and presents a review of the bacterial degradation of pyridine and its derivatives, indole, isoquinoline, and quinoline and its derivatives. The bacterial metabolism of these compounds under different redox conditions – by aerobic, nitrate-reducing, sulfate-reducing and methanogenic bacteria – is discussed. However, in natural habitats, various environmental factors, such as sorption phenomena, also influence bacterial conversion processes. Thus, both laboratory and field studies are necessary to aid our understanding of biodegradation in natural ecosystems and assist the development of strategies for bioremediation of polluted sites. Occurring predominantly near (former) wood-treatment facilities, creosote is a frequent contaminant of soil, subsoil, groundwater, and aquifer sediments. In situ as well as withdrawal-and-treatment techniques have been designed to remediate such sites, which are polluted with complex mixtures of aromatic and heterocyclic compounds.
355 citations
TL;DR: Culture conditions of Schizochytrium limacinum SR21 was thought to be a promising resource for microbial DHA production yielding a good level of productivity as well as a simple polyunsaturated fatty acid profile.
Abstract: Culture conditions of Schizochytrium limacinum SR21 for the purpose of microbial docosahexaenoic acid (DHA) production were investigated. The strain SR21 showed a wide tolerance to salinity; that is, the optimum salinity was between 50% and 200% that of sea water. Monosaccharides (glucose and fructose) and glycerol supported good cell growth and DHA yield. Di- and polysaccharides, oleic acid, and linseed oil gave low DHA yields. A high content of DHA (more than 30% of total fatty acids) was obtained from culture on glucose, fructose, and glycerol, and also the strain had simple polyunsaturated fatty acid profiles. The major polyunsaturated fatty acids other than DHA were n-6 docosapentaenoic acid only, and the contents of icosapentaenoic acid and arachidonic acid were less than 1%. Using corn steep liquor as a nitrogen source, a high total fatty acid content was obtained. The total fatty acid content in the dry cell weight increased as the concentration of the nitrogen source decreased, reached more than 50%. An increase in carbon source concentration led to a high DHA yield. A maximum DHA yield of more than 4 g/l was obtained in both glucose and glycerol media at 9% and 12% respectively. S. limacinum SR21 was thought to be a promising resource for microbial DHA production yielding a good level of productivity as well as a simple polyunsaturated fatty acid profile.
354 citations
TL;DR: Sourdough lactic acid bacteria, cultivated in wheat flour hydrolysate, produced antimould compounds that inhibited moulds related to bread spoilage such as Fusarium, Penicillium, Aspergillus and Monilia.
Abstract: Sourdough lactic acid bacteria, cultivated in wheat flour hydrolysate, produced antimould compounds. The antimould activity varied greatly among the strains and was mainly detected within obligately heterofermentative Lactobacillus spp. Among these, Lb. sanfrancisco CB1 had the largest spectrum. It inhibited moulds related to bread spoilage such as Fusarium, Penicillium, Aspergillus and Monilia. A mixture of acetic, caproic, formic, propionic, butyric and n-valeric acids, acting in a synergistic way, was responsible for the antimould activity. Caproic acid played a key role in inhibiting mould growth.
343 citations
TL;DR: There is a continuing need to isolate microbes that are able to function under extreme conditions and an urgent need to explore these extremophiles for their ability to produce biosurfactants that can function suitably under the conditions prevailing when they are applied.
Abstract: The interest in industrial biotechnology and its importance opens up challenging possibilities of research in this area. Surfactants have long been among the most versatile of process chemicals. Their market is extremely competitive and manufacturers will have to expand their arsenal to develop products for the year 2000 and beyond. Biosurfactants are one of the most promising compounds in this regard. A review of the literature reveals that studies on oil-degrading and biosurfactant-producing microorganisms deal almost exclusively with their synthesis in moderate environments. Biosurfactants and the microbes that produce them have numerous industrial, medical and environmental applications, which frequently involve exposure to extremes of temperatures, pressure, ionic strength, pH and organic solvents. Hence, there is a continuing need to isolate microbes that are able to function under extreme conditions. There is an urgent need to explore these extremophiles for their ability to produce biosurfactants that can function suitably under the conditions prevailing when they are applied.
320 citations
TL;DR: Novel oligomers that resist digestion in the upper gut were prepared from oat mixed-linked β-glucan and xylan by enzymatic hydrolysis with lichenase of Bacillus subtilis and x Dylanase of Trichoderma reesei respectively, which enhanced the growth of health-promoting probiotic strains as compared with intestinal bacterial growth, but not to a significant level.
Abstract: Novel oligomers that resist digestion in the upper gut were prepared from oat mixed-linked β-glucan and xylan by enzymatic hydrolysis with lichenase of Bacillus subtilis and xylanase of Trichoderma reesei respectively. The low-molecular-mass hydrolysis products of β-glucan and xylan were compared with fructooligomers and raffinose in their ability to provide growth substrates for probiotic (Lactobacillus and Bifidobacterium) and intestinal (Bacteroides, Clostridium and Escherichia coli) strains in vitro. A degradation profile of each carbohydrate and total sugar consumption were analysed with HPLC, and bacterial growth rate with an automatic turbidometer, the Bioscreen C system. β-Glucooligomers and xylooligomers both enhanced the growth of health-promoting probiotic strains as compared with intestinal bacterial growth, but not to a significant level. Raffinose stimulated the probiotic strains significantly, whereas fructooligomers induced high average growth for intestinal bacteria also.
295 citations
TL;DR: Deamination, COD degradation and biogas production decreased at lower and higher ammonia concentrations and hydrogen was formed in addition to methane, indicating that the thermophilic flora tolerated significantly more NH3 than the mesophilicFlora.
Abstract: The influence of ammonia on the anaerobic degradation of peptone by mesophilic and thermophilic populations of biowaste was investigated. For peptone concentrations from 5 g l−1 to 20 g l−1 the mesophilic population revealed a higher rate of deamination than the thermophilic population, e.g. 552 mg l−1 day−1 compared to 320 mg l−1 day−1 at 10 g l−1 peptone. The final degree of deamination of the thermophilic population was, however, higher: 102 compared to 87 mg NH3/g peptone in the mesophilic cultures. If 0.5–6.5 g l−1 ammonia was added to the mesophilic biowaste cultures, deamination of peptone, degradation of its chemical oxygen demand (COD) and formation of biogas were increasingly inhibited, but no hydrogen was formed. The thermophilic biowaste cultures were most active if around 1 g ammonia l−1 was present. Deamination, COD degradation and biogas production decreased at lower and higher ammonia concentrations and hydrogen was formed in addition to methane. Studies of the inhibition by ammonia of peptone deamination, COD degradation and methane formation revealed a K
i (50%) for NH3 of 92, 95 and 88 mg l−1 at 37 °C and 251, 274 and 297 mg l−1 at 55 °C respectively. This indicated that the thermophilic flora tolerated significantly more NH3 than the mesophilic flora. In the mesophilic reactor effluent 4.6 × 108 peptone-degrading colony-forming units (cfu)/ml were culturable, whereas in the thermophilic reactor effluent growth of only 5.6 × 107 cfu/ml was observed.
TL;DR: There was significant variation in the physical appearance of the alkali-soluble glucans and the relative viscosity of suspensions of these glucans, suggesting the yeasts could represent novel sources of polysaccharides with industrial and medical applications.
Abstract: Cell walls, representing 26%–32% of the cell dry weight, were prepared from several strains of the yeasts Kloeckera apiculata, Debaryomyces hansenii, Zygosaccharomyces bailii,Kluyveromyces marxianus and Saccharomyces cerevisiae. Extraction of the walls with potassium hydroxide at 4 °C, followed by saturation of the alkali-soluble extract with ammonium sulphate gave fractions of mannoprotein, alkali-soluble glucan and alkali-insoluble glucan. Chitin was associated with the alkali-insoluble glucan. The proportions of the different fractions within the walls varied with the species and strain. Mannoprotein comprised between 25% and 34% of the walls, the content of alkali-insoluble glucan ranged from 15% to 48%, and the content of alkali-soluble glucan ranged from 10% to 48%. There was significant variation in the physical appearance of the alkali-soluble glucans and the relative viscosity of suspensions of these glucans. The yeasts could represent novel sources of polysaccharides with industrial and medical applications.
TL;DR: It is suggested that HMG-CoA reductase is not the only rate-limiting step in sterol synthesis and its overexpression cannot significantly influence this pathway beyond the sterol precursor squalene.
Abstract: The enzyme 3-hydroxy-3-methylglutaryl-coenzyme-A (HMG-CoA) reductase is known as the rate-limiting enzyme in early sterol biosynthesis in eukaryotic cells. To eliminate this regulation in the yeast Saccharomyces cerevisiae, a truncated HMG1 gene, producing a form of the enzyme that lacks the membrane-binding region (i.e. amino acids 1–552), was constructed and overexpressed in this yeast. The transformed strains accumulated large amounts of the sterol precursor squalene, while the levels of ergosterol and a number of other sterol compounds were only slightly elevated. These findings suggest that HMG-CoA reductase is not the only rate-limiting step in sterol synthesis and its overexpression cannot significantly influence this pathway beyond the sterol precursor squalene.
TL;DR: A modified type of flat-plate photobioreactor designed for cultivation of a high-CO2-tolerant unicellular green alga Chlorococcum littorale and the potential of biomass production under extremely high CO2 concentrations was evaluated.
Abstract: To test the feasibility of CO2 remediation by microalgal photosynthesis, a modified type of flat-plate photobioreactor [Hu et al. (1996) Biotechnol Bioeng 51:51–60] has been designed for cultivation of a high-CO2-tolerant unicellular green alga Chlorococcum littorale. The modified reactor has a narrow light path in which intensive turbulent flow is provided by streaming compressed air through perforated tubing into the culture suspension. The length of the reactor light path was optimized for the productivity of biomass. The interrelationship between cell density and productivity, as affected by incident light intensity, was quantitatively assessed. Cellular ultrastructural and biochemical changes in response to ultrahigh cell density were investigated. The potential of biomass production under extremely high CO2 concentrations was also evaluated. By growing C. littorale cells in this reactor, a CO2 fixation rate of 16.7 g CO2 l−1 24 h−1 (or 200.4 g CO2 m−2 24 h−1) could readily be sustained at a light intensity of 2000 μmol m−2 s−1 at 25 °C, and an ultrahigh cell density of well over 80 g l−1 could be maintained by daily replacing the culture medium.
TL;DR: At any of the pH values tested, excess glycerol in the culture enhanced the butanediol yield, and the undissociated acid being a stronger trigger than the less toxic diols and acid anions.
Abstract: Klebsiella pneumoniae was shown to convert glycerol to 1,3-propanediol, 2,3-butanediol and ethanol under conditions of uncontrolled pH. Formation of 2,3-butanediol starts with some hours' delay and is accompanied by a reuse of the acetate that was formed in the first period. The fermentation was demonstrated in the type strain of K. pneumoniae, but growth was better with the more acid-tolerant strain GT1, which was isolated from nature. In continuous cultures in which the pH was lowered stepwise from 7.3 to 5.4, 2,3-butanediol formation started at pH 6.6 and reached a maximum yield at pH 5.5, whereas formation of acetate and ethanol declined in this pH range. 2,3-Butanediol and acetoin were also found among the products in chemostat cultures grown at pH 7 under conditions of glycerol excess but only with low yields. At any of the pH values tested, excess glycerol in the culture enhanced the butanediol yield. Both effects are seen as a consequence of product inhibition, the undissociated acid being a stronger trigger than the less toxic diols and acid anions. The possibilities for using the fermentation type described to produce 1,3-propanediol and 2,3-butanediol almost without by-products are discussed.
TL;DR: It is demonstrated that renewable and inexpensive plant oils are excellent carbon sources for efficient production of PHA using A. eutrophus strains from olive oil.
Abstract: The ability of Alcaligenes eutrophus to grow and produce polyhydroxyalkanoates (PHA) on plant oils was evaluated. When olive oil, corn oil, or palm oil was fed as a sole carbon source, the wild-type strain of A. eutrophus grew well and accumulated poly(3-hydroxybutyrate) homopolymer up to approximately 80% (w/w) of the cell dry weight during its stationary growth phase. In addition, a recombinant strain of A. eutrophus PHB−4 (a PHA-negative mutant), harboring a PHA synthase gene from Aeromonas caviae, was revealed to produce a random copolyester of 3-hydroxybutyrate and 3-hydroxyhexanoate from these plant oils with a high cellular content (approximately 80% w/w). The mole fraction of 3-hydroxyhexanoate units was 4–5 mol% whatever the structure of the triglycerides fed. The polyesters produced by the A. eutrophus strains from olive oil were 200–400 kDa (the number-average molecular mass). The results demonstrate that renewable and inexpensive plant oils are excellent carbon sources for efficient production of PHA using A. eutrophus strains.
TL;DR: This review focuses on the current knowledge of the mechanistic action of nisin and pediocin-like bacteriocins, the requirement for a cell factor such as a membrane protein, the influence of membrane potential, pH, and lipid composition on the of specificity and efficacy of bacteriOCins, and the roles of specific amino acids and structural domains of the bacteriocoins in their action.
Abstract: Nisin and pediocin PA-1 are examples of bacteriocins from lactic acid bacteria (LAB) that have found practical applications as food preservatives. Like other natural antimicrobial peptides, LAB bacteriocins act primarily at the cytoplasmic membranes of susceptible microorganisms. Studies with in vivo as well as in␣vitro membrane systems are directed toward understanding how bacteriocins interact with membranes so as to provide a mechanistic basis for their rational applications. The dissipation of proton motive force was identified early on as the common mechanism for the lethal activity of LAB bacteriocin. Models for nisin/membrane interactions propose that the peptide forms poration complexes in the membrane through a multi-step process of binding, insertion, and pore formation. This review focuses on the current knowledge of: (1) the mechanistic action of nisin and pediocin-like bacteriocins, (2) the requirement for a cell factor such as a membrane protein, (3) the influence of membrane potential, pH, and lipid composition on the of specificity and efficacy of bacteriocins, and (4) the roles of specific amino acids and structural domains of the bacteriocins in their action.
TL;DR: Characterization of the purified protein by Western blot, amino acid composition analysis, and matrix-assisted laser desorption ionization/time-of-flight mass spectrometry confirms it to be spider dragline silk.
Abstract: A partial cDNA clone, from the 3′ end of the dragline silk gene was isolated from Nephila clavipes major ampullate glands. This clone contains a 1.7-kb insert, consisting of a repetitive coding region of 1.4-kb and a 0.3-kb nonrepetitive coding region; 1.5-kb of the 1.7-kb fragment was cloned into Escherichia coli and a␣43-kDa recombinant silk protein was expressed. Characterization of the purified protein by Western blot, amino acid composition analysis, and matrix-assisted laser desorption ionization/time-of-flight mass spectrometry confirms it to be spider dragline silk.
TL;DR: A kinetic model of the fermentative production of lactic acid from glucose by Lactococcus lactis ssp.
Abstract: A kinetic model of the fermentative production of lactic acid from glucose by Lactococcus lactis ssp. lactis ATCC 19435 in whole-wheat flour has been developed. The model consists of terms for substrate and product inhibition as well as for the influence of pH and temperature. Experimental data from fermentation experiments under different physical conditions were used to fit and verify the model. Temperatures above 30 °C and pH levels below 6 enhanced the formation of by-products and d-lactic acid. By-products were formed in the presence of maltose only, whereas d-lactic acid was formed independently of the presence of maltose although the amount formed was greater when maltose was present. The lactic acid productivity was highest between 33 °C and 35 °C and at pH 6. In the concentration interval studied (up to 180 g l−1 glucose and 89 g l−1 lactic acid) simulations showed that both substances were inhibiting. Glucose inhibition was small compared with the inhibition due to lactic acid.
TL;DR: This report reports the first report of fructan production by a Lactobacillus species, which increased with increasing sucrose concentrations and involved extracellular sucrase-type enzymes.
Abstract: A total of 182 Lactobacillus strains were screened for production of extracellular polysaccharides (EPS) by a new method: growth in liquid media with high sugar concentrations. Sixty EPS-positive strains were identified; 17 strains produced more than 100 mg/l soluble EPS. Sucrose was an excellent substrate for abundant EPS synthesis. The ability to produce glucans appears to be widespread in the genus Lactobacillus. The monosaccharide composition of EPS produced by Lactobacillus reuteri strain LB 121 varied with the growth conditions (solid compared to liquid medium) and the sugar substrates (sucrose or raffinose) supplied in the medium. Strain LB 121 produced both a glucan and a fructan on sucrose, but only a fructan on raffinose. This is the first report of fructan production by a Lactobacillus species. EPS production increased with increasing sucrose concentrations and involved extracellular sucrase-type enzymes.
TL;DR: The role of bacterial plasmids in natural genetic exchange between inoculated and indigenous sludge bacteria, and in the construction of new genetically modified organisms, are dealt with.
Abstract: Bioaugmentation of activated sludge systems with specialised bacterial strains could be a powerful tool to improve several aspects in wastewater treatment processes, such as improved flocculation and degradation of recalcitrant compounds. This review focuses on the addition of strains to activated sludge to enhance the biodegradation of recalcitrant compounds, either through the activity of the inoculated strain or after transfer of degradative plasmids to activated sludge bacteria. Different factors that improve the aggregation of the sludge flocs and their influence on biodegradation are described. This review further deals with the role of bacterial plasmids in natural genetic exchange between inoculated and indigenous sludge bacteria, and in the construction of new genetically modified organisms. The few successful cases of bioaugmentation described in this review, together with future research, must lead to a better understanding of sludge bioaugmentation.
TL;DR: Continuous hydrogen gas evolution by self-flocculated cells of Enterobacter aerogenes, a natural isolate HU-101 and its mutant AY-2, was performed in a packed-bed reactor under glucose-limiting conditions in a minimal medium.
Abstract: Continuous hydrogen gas evolution by self-flocculated cells of Enterobacter aerogenes, a natural isolate HU-101 and its mutant AY-2, was performed in a packed-bed reactor under glucose-limiting conditions in a minimal medium. The flocs that formed during the continuous culture were retained even when the dilution rate was increased to 0.9 h−1. The H2 production rate increased linearly with increases in the dilution rate up to 0.67 h−1, giving maximum H2 production rates of 31 and 58 mmol l−1 h−1 in HU-101 and AY-2 respectively, at a dilution rate of more than 0.67 h−1. The molar H2 yield from glucose in AY-2 was maintained at about 1.1 at dilution rates between 0.08 h−1 and 0.67 h−1, but it decreased rapidly at dilution rates more than 0.8 h−1.
TL;DR: Progress might be achieved by screening more cyanobacterial strains for their ability to produce and evolve hydrogen, by genetically manipulating specific strains as well as by improving the conditions for cultivation in bioreactors.
Abstract: In discussions about alternatives to our current fossil energy sources, basic and applied research leading to biological production of molecular hydrogen utilizing cyanobacteria deserves serious at ...
TL;DR: Pathways for their enzymatic degradation and the organisation of the corresponding degradative genes have been elucidated and biotechnological applications will exploit theDegradative potential of such microorganisms for bioremediation of contaminated sites.
Abstract: Polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF; PCDD/F, dioxins) have not been commercially produced in bulk amounts, as were polychlorinated biphenyls and other haloaromatic organics. Within the past two decades a lot␣of information has accumulated on the biodegradation of PCDD/F and other dioxin-like compounds because of their toxicity and because of significant environmental concern about many congeners of this class of chemicals. PCDD/F are subjected to reductive dehalogenations leading to less halogenated congeners, which can be attacked efficiently by fungal and bacterial oxidases and dioxygenases. In several cases these compounds can be utilized as carbon and energy sources. Pathways for their enzymatic degradation and the organisation of the corresponding degradative genes have been elucidated. Consequently, biotechnological applications will exploit the degradative potential of such microorganisms for bioremediation of contaminated sites.
TL;DR: The production of feruloyl esterase activity by Bacillus spp.
Abstract: The production of feruloyl esterase activity by Bacillus spp. and lactobacilli can be detected in an agar-plate assay. The assay involves the substitution of the main carbon source in specific agar with ethyl ferulate. A number of Bacillus spp., predominantly B. subtilis strains, were found to exhibit feruloyl esterase activity by this method. Of the examined lactobacilli, Lb. fermentum (NCFB 1751) showed the highest level of ferulic acid esterase activity. The enzyme was released from harvested cells by sonication and showed pH and temperature optima of 6.5 and 30 °C respectively.
TL;DR: In this paper, the authors investigated the effect of 14C-radiol-labeled hexadecane and naphthalene on the mineralization of an oil-impacted soil.
Abstract: Oil spills occur in the Antarctic when fuel oils such as JP8 jet fuel are moved or stored. Hydrocarbons, both n-alkanes and aromatic compounds, have been detected in oil-contaminated soils of the Ross Dependency. In such areas hydrocarbon-degrading microbes, if naturally occurring, could be used for clean-up. Soil samples from oil-impacted and control sites were analysed for hydrocarbon-degrading microbes and for a range of parameters known to limit biodegradative activity. Soils were analysed for water content, pH, concentrations of nutrients (N and P) and electrical conductivity. Numbers of culturable heterotrophic bacteria and hydrocarbon degraders were greater in some of the oil-contaminated samples. Mineralisation studies with 14C-radiolabelled hexadecane and naphthalene demonstrated that nitrogen amendments significantly enhanced hydrocarbon mineralisation rates in an oil-impacted soil.
TL;DR: The white-rot fungus Trametes trogii excretes a main laccase showing a molecular mass of 70 kDa, acidic isoelectric point and N-terminal sequence homol-ogous to that of several phenol oxidases, which oxidizes a number of phenolic and non-phenolic compounds.
Abstract: The white-rot fungus Trametes trogii excretes a main laccase showing a molecular mass of 70 kDa, acidic isoelectric point and N-terminal sequence homologous to that of several phenol oxidases. The purified enzyme oxidizes a number of phenolic and non-phenolic compounds; recalcitrant molecules may be converted into substrates by introducing, in the correct position, o- or p-orienting ring-activating groups.
TL;DR: In this paper, the authors investigated the biosynthesis of poly(hydroxyalkanoates) (PHA) by Pseudomonas resinovorans from triglyceride substrates, and determined the repeat unit composition of the polymers by gas chromatography (GC) and GC/mass spectrometry of the β-hydroxalkanoate methyl esters from the hydrolyzed polymers.
Abstract: The biosynthesis of poly(hydroxyalkanoates) (PHA) by Pseudomonas resinovorans from triglyceride substrates was investigated. Each triglyceride, whether animal fat or vegetable oil, supported cellular growth to relatively high average cell yields (3.3 ± 0.2 g/l). PHA yields ranged from 1.1 g/l to 2.1 g/l, representing approximately 45% of the bacterial cell dry weight. The repeat-unit composition of the polymers was determined by gas chromatography (GC) and GC/mass spectrometry of the β-hydroxyalkanoate methyl esters from the hydrolyzed polymers. With the exception of PHA from soybean oil (PHA-soy), each polyester was composed of β-hydroxyacyl moieties with chain lengths ranging from C4 to C14, with C8 and C10 being the predominant species. PHA-soy contained an additional fraction (2%) of C16 monomers. The alkyl side-chains of the PHA contained varying degrees of unsaturation. PHA from coconut oil was composed entirely of saturated side-chains, whereas PHA-soy contained 4.2 mol% olefinic groups in its side-chains. The increase in the degree of side-chain unsaturation caused decreased melting temperatures, enthalpies of fusion, and glass transition temperatures. The molar masses of the polymers were relatively constant and ranged from 6.5 × 104 to 10.1 × 104 g/mol.
TL;DR: The maximum food signal production was recorded during the late exponential growth phase and the efficacy of the bacterial signal is much lower compared to the food signal found in insects.
Abstract: Photorhabdus luminescens are bacterial symbionts of entomopathogenic nematodes of the genus Heterorhabditis. The bacto-helminthic complexes are used in biocontrol of insect pests in cryptic environments. For in vitro production, liquid media are incubated with P. luminescens for 24 h prior to the inoculation of nematode dauer juveniles. The nematodes develop to self-fertilizing hermaphrodites and produce offspring. The exit from the developmentally arrested dauer stage (recovery) is a response to a yet undescribed food signal. Major process instability is caused by low and unsynchronized recovery of the dauers. In living insects, dauer recovery is approximately 95% within 1 day. In liquid cultures of P. luminescens the recovery is spread over several days and varies between 0 and 81%. In complex culture media no food signal was detected. A food signal is produced by P. luminescens and excreted into the culture medium. The maximum food signal production was recorded during the late exponential growth phase. Compared to the food signal found in insects, the efficacy of the bacterial signal is much lower. The reasons for the variable activity of the bacterial food signal and its function during the nematode life cycle are discussed.
TL;DR: The results suggest that cost-effective production of PHB is possible by fed-batch culture of recombinant E. coli using concentrated whey solution as a substrate.
Abstract: Recombinant Escherichia coli strain GCSC 6576, harboring a high-copy-number plasmid containing the Ralstonia eutropha genes for polyhydroxyalkanoate (PHA) synthesis and the E. coli ftsZ gene, was employed to produce poly-(3-hydroxybutyrate) (PHB) from whey. pH-stat fed-batch fermentation, using whey powder as the nutrient feed, produced cellular dry weight and PHB concentrations of 109 g l−1 and 50 g l−1 respectively in 47 h. When concentrated whey solution containing 210 g l−1 lactose was used as the nutrient feed, cellular dry weight and PHB concentrations of 87 g l−1 and 69 g l−1 respectively could be obtained in 49 h by pH-stat fed-batch culture. The PHB content was as high as 80% of the cellular dry weight. These results suggest that cost-effective production of PHB is possible by fed-batch culture of recombinant E. coli using concentrated whey solution as a substrate.