Showing papers in "Fems Microbiology Letters in 2008"

Antibacterial activity of ZnO nanoparticle suspensions on a broad spectrum of microorganisms

Abstract: Nanoparticle metal oxides represent a new class of important materials that are increasingly being developed for use in research and health-related applications. Highly ionic metal oxides are interesting not only for their wide variety of physical and chemical properties but also for their antibacterial activity. Although the in vitro antibacterial activity and efficacy of regular zinc oxides have been investigated, little is known about the antibacterial activity of nanoparticles of ZnO. Preliminary growth analysis data suggest that nanoparticles of ZnO have significantly higher antibacterial effects on Staphylococcus aureus than do five other metal oxide nanoparticles. In addition, studies have clearly demonstrated that ZnO nanoparticles have a wide range of antibacterial effects on a number of other microorganisms. The antibacterial activity of ZnO may be dependent on the size and the presence of normal visible light. The data suggest that ZnO nanoparticles have a potential application as a bacteriostatic agent in visible light and may have future applications in the development of derivative agents to control the spread and infection of a variety of bacterial strains.

Bacterial endophytes: recent developments and applications

Abstract: Endophytic bacteria have been found in virtually every plant studied, where they colonize the internal tissues of their host plant and can form a range of different relationships including symbiotic, mutualistic, commensalistic and trophobiotic Most endophytes appear to originate from the rhizosphere or phyllosphere; however, some may be transmitted through the seed Endophytic bacteria can promote plant growth and yield and can act as biocontrol agents Endophytes can also be beneficial to their host by producing a range of natural products that could be harnessed for potential use in medicine, agriculture or industry In addition, it has been shown that they have the potential to remove soil contaminants by enhancing phytoremediation and may play a role in soil fertility through phosphate solubilization and nitrogen fixation There is increasing interest in developing the potential biotechnological applications of endophytes for improving phytoremediation and the sustainable production of nonfood crops for biomass and biofuel production

How many species are infected with Wolbachia?--A statistical analysis of current data.

Abstract: Wolbachia are intracellular bacteria found in many species of arthropods and nematodes They manipulate the reproduction of their arthropod hosts in various ways, may play a role in host speciation and have potential applications in biological pest control Estimates suggest that at least 20% of all insect species are infected with Wolbachia These estimates result from several Wolbachia screenings in which numerous species were tested for infection; however, tests were mostly performed on only one to two individuals per species The actual percent of species infected will depend on the distribution of infection frequencies among species We present a meta-analysis that estimates percentage of infected species based on data on the distribution of infection levels among species We used a beta-binomial model that describes the distribution of infection frequencies of Wolbachia, shedding light on the overall infection rate as well as on the infection frequency within species Our main findings are that (1) the proportion of Wolbachia-infected species is estimated to be 66%, and that (2) within species the infection frequency follows a ‘most-or-few’ infection pattern in a sense that the Wolbachia infection frequency within one species is typically either very high (>90%) or very low (<10%)

High‐pressure processing – effects on microbial food safety and food quality

Abstract: High-pressure processing (HPP) is a nonthermal process capable of inactivating and eliminating pathogenic and food spoilage microorganisms. This novel technology has enormous potential in the food industry, controlling food spoilage, improving food safety and extending product shelf life while retaining the characteristics of fresh, preservative-free, minimally processed foods. As with other food processing methods, such as thermal processing, HPP has somewhat limited applications as it cannot be universally applied to all food types, such as some dairy and animal products and shelf-stable low-acid foods. Herein, we discuss the effects of high-pressure processing on microbial food safety and, to a lesser degree, food quality.

Update on macrolide–lincosamide–streptogramin, ketolide, and oxazolidinone resistance genes

Abstract: This Minireview summarizes the changes in the field of bacterial resistance to macrolide, lincosamide, streptogramin, ketolide, and oxazolidinone (MLSKO) antibiotics since the nomenclature review in 1999. A total of 66 genes conferring resistance to this group of antibiotics has now been identified and includes 13 new rRNA methylase genes, four ATP-binding transporter genes coding for efflux proteins, and five new inactivating enzymes. During this same time period, 73 new genera carrying known rRNA methylase genes and 87 new genera carrying known efflux and/or inactivating genes have been recognized. The number of bacteria with mutations in the genes for 23S rRNA, L4 and L22 ribosomal proteins, resulting in reduced susceptibility to some members of the group of MLSKO antibiotics has also increased and now includes nine different Gram-positive and 10 different Gram-negative genera. New conjugative transposons carrying different MLSKO genes along with an increased number of antibiotics and/or heavy metal resistance genes have been identified. These mobile elements may play a role in the continued spread of the MLSKO resistance genes into new species, genera, and ecosystems.

Linkage of microbial ecology to phenotype: correlation of rumen microbial ecology to cattle's feed efficiency.

Abstract: Linkage of rumen microbial structure to host phenotypical traits may enhance the understanding of host-microbial interactions in livestock species. This study used culture-independent PCR-denaturing gradient gel electrophoresis (PCR-DGGE) to investigate the microbial profiles in the rumen of cattle differing in feed efficiency. The analysis of detectable bacterial PCR-DGGE profiles showed that the profiles generated from efficient steers clustered together and were clearly separated from those obtained from inefficient steers, indicating that specific bacterial groups may only inhabit in efficient steers. In addition, the bacterial profiles were more likely clustered within a certain breed, suggesting that host genetics may play an important role in rumen microbial structure. The correlations between the concentrations of volatile fatty acids and feed efficiency traits were also observed. Significantly higher concentrations of butyrate (P < 0.001) and valerate (P = 0.006) were detected in the efficient steers. Our results revealed potential associations between the detectable rumen microbiota and its fermentation parameters with the feed efficiency of cattle.

Nitrifier genomics and evolution of the nitrogen cycle

Abstract: Advances in technology have tremendously increased high throughput whole genome-sequencing efforts, many of which have included prokaryotes that facilitate processes in the extant nitrogen cycle. Molecular genetic and evolutionary analyses of these genomes paired with advances in postgenomics, biochemical and physiological experimentation have enabled scientists to reevaluate existing geochemical and oceanographic data for improved characterization of the extant nitrogen cycle as well as its evolution since the primordial era of planet Earth. Based on the literature and extensive new data relevant to aerobic and anaerobic ammonia oxidation (ANAMMOX), the natural history of the nitrogen-cycle has been redrawn with emphasis on the early roles of incomplete denitrification and ammonification as driving forces for emergence of ANAMMOX as the foundation for a complete nitrogen cycle, and concluding with emergence of nitrification in the oxic era.

N-acylhomoserine lactone regulates violacein production in Chromobacterium violaceum type strain ATCC 12472.

Abstract: In tests, Chromobacterium violaceum ATCC 12472 produced several N-acyl-L-homoserine lactones (AHLs). Of these, N-(3-hydroxydecanoyl)-L-homoserine lactone was dominant, and controlled violacein production by quorum sensing. Strain VIR07, an AHL-deficient mutant, did not produce violacein. Violacein production in VIR07 was induced by adding long-chain AHLs (C10-C16), but was inhibited by adding short-chain AHLs (C4-C8). Strain VIR07 showed the response of violacein production when AHLs diffused from a variety of AHL-producing bacteria on agar plates, and thus might be a useful biosensor for recognizing exogenous AHLs.

Diversity of endophytic bacteria from Eucalyptus species seeds and colonization of seedlings by Pantoea agglomerans

Abstract: The diversity and beneficial characteristics of endophytic microorganisms have been studied in several host plants. However, information regarding naturally occurring seed-associated endophytes and vertical transmission among different life-history stages of hosts is limited. Endophytic bacteria were isolated from seeds and seedlings of 10 Eucalyptus species and two hybrids. The results showed that endophytic bacteria, such as Bacillus, Enterococcus, Paenibacillus and Methylobacterium, are vertically transferred from seeds to seedlings. In addition, the endophytic bacterium Pantoea agglomerans was tagged with the gfp gene, inoculated into seeds and further reisolated from seedlings. These results suggested a novel approach to change the profile of the plants, where the bacterium is a delivery vehicle for desired traits. This is the first report of an endophytic bacterial community residing in Eucalyptus seeds and the transmission of these bacteria from seeds to seedlings. The bacterial species reported in this work have been described as providing benefits to host plants. Therefore, we suggest that endophytic bacteria can be transmitted vertically from seeds to seedlings, assuring the support of the bacterial community in the host plant.

Members of the phylum Acidobacteria are dominant and metabolically active in rhizosphere soil.

Abstract: A culture-independent survey was performed to search for 16S rRNA gene sequences representing dominant and metabolically active bacteria in rhizosphere soil PCR- and reverse transcription-PCR-derived clone libraries were constructed from DNA and RNA directly extracted from the soil sample Acidobacteria-related sequences occupied an unusually large proportion (>50%) of both rDNA- and rRNA-derived clone libraries This study suggested that the bacteria belonging to the phylum Acidobacteria might be numerically dominant as well as metabolically active in the soil sample, implying that the phylum Acidobacteria might be highly involved in the biogeochemical cycles of the rhizosphere soil

Factors associated with adherence to and biofilm formation on polystyrene by Stenotrophomonas maltophilia: the role of cell surface hydrophobicity and motility

Abstract: We tested 40 clinical Stenotrophomonas maltophilia strains to investigate the possible correlation between adherence to and formation of biofilm on polystyrene, and cell surface properties such as hydrophobicity and motility. Most of the strains were able to adhere and form biofilm, although striking differences were observed. Eleven (27.5%) of the strains were hydrophobic, with hydrophobicity greatly increasing as S. maltophilia attached to the substratum. A positive correlation was observed between hydrophobicity and levels of both adhesion and biofilm formation. Most of the isolates showed swimming and twitching motility. A highly significant negative correlation was observed between swimming motility and level of hydrophobicity. Hydrophobicity is thus a significant determinant of adhesion and biofilm formation on polystyrene surfaces in S. maltophilia.

Nitrogen removal performance using anaerobic ammonium oxidation at low temperatures

Abstract: An anaerobic ammonium oxidation (anammox) process for ammonia-rich wastewater treatment has not been reported at temperatures below 15 °C. This study used a gel carrier with entrapped anammox bacteria to obtain a stable nitrogen removal performance at low temperatures. In a continuous feeding test, a high nitrogen conversion rate (6.2 kg N m−3 day−1) was confirmed at 32 °C. Nitrogen removal activity decreased gradually with decreasing operation temperature; however, it still occurred at 6 °C. Nitrogen conversion rates at 22 and 6.3 °C were 2.8 and 0.36 kg N m−3 day−1, respectively. Moreover, the stability of anammox activity below 20 °C was confirmed for more than 130 days. In batch experiments, anammox gel carriers were characterized with respect to temperature. The optimum temperature for anammox bacteria was found to be 37 °C. Furthermore, it was clear that the temperature dependence changed at about 28 °C. The apparent activation energy in the temperature range from 22 to 28 °C was calculated as 93 kJ mol−1, and that in the range from 28 to 37 °C was 33 kJ mol−1. This value agrees with the result of a continuous feeding test (94 kJ mol−1, between 6 and 22 °C). The nitrogen removal performance demonstrated at the low temperatures used in this study will open the door for the application of anammox processes to many types of industrial wastewater treatment.

Stress induction of mycotoxin biosynthesis genes by abiotic factors

Abstract: Systematic expression analysis of mycotoxin biosynthesis genes by real-time PCR and microarray was carried out to examine the relationship between growth and general expression patterns in relation to single environmental factors such as temperature, water activity ( a w) and pH and water activity × temperature interactions. For single parameters, one major peak of expression occurred close to optimum growth conditions. However, a second minor peak was observed under suboptimal growth conditions, when intermediate environmental stress was imposed on Aspergillus parasiticus ( afl genes), Penicillium verrucosum ( ota genes) and Fusarium culmorum ( tri genes). This expression profile pattern was more pronounced in relation to changes in temperature and a w than to pH. In a two-factorial experimental design with temperature × a w regimes, again two peaks of expression were observed for cluster genes after microarray analysis, one close to those giving optimal growth and one under imposed stress conditions. Interestingly, when the activity of single genes of the microarray data were plotted in relation to the two parameters, again a two-peak expression profile became obvious independently for both parameters. Expression of the mycotoxin biosynthesis genes was followed exactly by phenotypic mycotoxin production. This expression profile appears to be generic across the mycotoxigenic fungi examined.

Growth with high planktonic biomass in Shewanella oneidensis fuel cells

Abstract: Shewanella oneidensis MR-1 grew for over 50 days in microbial fuel cells, incompletely oxidizing lactate to acetate with high recovery of the electrons derived from this reaction as electricity. Electricity was produced with lactate or hydrogen and current was comparable to that of electricigens which completely oxidize organic substrates. However, unlike fuel cells with previously described electricigens, in which cells are primarily attached to the anode, at least as many of the S. oneidensis cells were planktonic as were attached to the anode. These results demonstrate that S. oneidensis may conserve energy for growth with an electrode serving as an electron acceptor and suggest that multiple strategies for electron transfer to fuel cell anodes exist.

The phage K lytic enzyme LysK and lysostaphin act synergistically to kill MRSA

Abstract: LysK is the endolysin from the staphylococcal bacteriophage K, and can digest the cell wall of many staphylococci. Lysostaphin is a bacteriocin secreted by Staphylococcus simulans to kill Staphylococcus aureus. Both LysK and lysostaphin have been shown to lyse methicillin-resistant S. aureus (MRSA). This study describes optimal reaction conditions for the recombinant His-tagged LysK protein (pH range pH 6-10, and 0.3-0.5 M NaCl), and C-His-LysK MIC (32.85+/-4.87 mug mL(-1)). LysK and lysostaphin demonstrate antimicrobial synergy by the checkerboard assay.

Animal models of mucosal Candida infection.

Abstract: Rodent models of oral, vaginal and gastrointestinal Candida infection are described and discussed in terms of their scientific merits. The common feature of all experimental mucosal Candida infections is the need for some level of host immunocompromise or exogenous treatment to ensure quantitatively reproducible disease. A growing literature describes the contributions of such candidiasis models to our understanding of certain aspects of fungal virulence and host response to mucosal Candida albicans challenge. Evidence to date shows that T-lymphocyte responses dominate host immune defences to oral and gastrointestinal challenge, while other, highly compartmentalized responses defend vaginal surfaces. By contrast the study of C. albicans virulence factors in mucosal infection models has only begun to unravel the complex of attributes required to define the difference between strongly and weakly muco-invasive strains.

Hydrogen peroxide production by Lactobacillus johnsonii NCC 533 and its role in anti-Salmonella activity

Abstract: The human intestinal isolate Lactobacillus johnsonii NCC 533 (La1) is a probiotic strain with well-documented antimicrobial properties. Previous research has identified the production of lactic acid and bacteriocins as important factors, but that other unidentified factors are also involved. We used the recently published genome sequence of L. johnsonii NCC 533 to search for novel antipathogen factors and identified three potential gene products that may catalyze the synthesis of the known antimicrobial factor hydrogen peroxide, H(2)O(2). In this work, we confirmed the ability of NCC 533 as well as eight different L. johnsonii strains and Lactobacillus gasseri to produce H(2)O(2) when resting cells were incubated in the presence of oxygen, and that culture supernatant containing NCC 533-produced H(2)O(2) was effective in killing the model pathogen Salmonella enterica serovar Typhimurium SL1344 in vitro.

Evidence that the potential for dissimilatory ferric iron reduction is widespread among acidophilic heterotrophic bacteria.

Abstract: Nineteen characterized strains and isolates of acidophilic heterotrophic bacteria were screened for their abilities to catalyse the reductive dissolution of the ferric iron mineral schwertmannite, under oxygen-limiting conditions. Acidocella facilis, Acidobacterium capsulatum, and all of the Acidiphilium, Acidocella and Acidobacterium-like isolates that grew in liquid cultures were able to reduce iron. In contrast, neither Acidisphaera rubrifaciens nor three Acidisphaera-like isolates tested were found to have the capacity for dissimilatory iron reduction. One of two iron-oxidizing Frateuria-like isolates also reduced iron under oxygen-limiting conditions. Microbial dissolution of schwertmannite was paralleled with increased concentrations of soluble ferrous iron and sulfate in microbial cultures, together with increased pH values and decreased redox potentials. While dissimilatory ferric iron reduction has been described previously for Acidiphilium spp., this is this first report of this capacity in Acidocella and the moderate acidophile Acidobacterium. The finding has significant implications for understanding of the biogeochemistry of acidic environments.

Rhizobial secreted proteins as determinants of host specificity in the rhizobium-legume symbiosis.

Abstract: Rhizobia are Gram-negative bacteria than can elicit the formation of specialized organs, called root nodules, on leguminous host plants. Upon infection of the nodules, they differentiate into nitrogen-fixing bacteroids. An elaborate signal exchange precedes the symbiotic interaction. In general, both rhizobia and host plants exhibit narrow specificity. Rhizobial factors contributing to this specificity include Nod factors and surface polysaccharides. It is becoming increasingly clear that protein secretion is important in determining the outcome of the interaction as well. This paper discusses our current understanding of the symbiotic role played by rhizobial secreted proteins, transported both by secretion systems that are of general use, such as the type I secretion system, and by specialized, host-targeting secretion systems, such as the type III, type IV and type VI secretion systems.

Enumeration of Archaea and Bacteria in seafloor basalt using real-time quantitative PCR and fluorescence microscopy

Abstract: A SYBR Green real-time quantitative PCR (Q-PCR) assay for the detection and quantification of Bacteria and Archaea present in the glassy rind of seafloor basalts of different ages and water depths is presented. Two sets of domain-specific primers were designed and validated for specific detection and quantification of bacterial and archaeal 16S rRNA genes in DNA extracted from basaltic glass. Total cell numbers were also estimated by fluorescence microscopy analysis of SYBR Gold-stained samples. The results from the two different approaches were concurrent, and Q-PCR results showed that the total number of cells present in basalts was in the range from 6 × 105 to 4 × 106 cells g−1 basaltic glass. Further, it was demonstrated that these cells were almost exclusively from the domain Bacteria. When applying the same methods on samples of different ages (22 years–0.1 Ma) and water depths (139–3390 mbsl), no significant differences in cell concentrations or in the relative abundance of Archaea and Bacteria were detected.

Quorum quenching activity in Anabaena sp. PCC 7120: identification of AiiC, a novel AHL‐acylase

Abstract: Many bacteria use quorum sensing (QS) to coordinate responses to environmental changes. In Gram-negative bacteria, the most extensively studied QS systems rely on the use of N-acylhomoserine lactones (AHLs) signal molecules. Some bacteria produce enzymes that are able to inactivate AHL signals produced by other bacteria and hence interfere with QS-mediated processes via a phenomenon known as quorum quenching. Acylase-type AHL degradation activity has been found in the biomass of the filamentous nitrogen-fixing cyanobacterium Anabaena (Nostoc) sp. PCC 7120, being absent from the culture media. The gene all3924 has been identified and cloned whose product exhibits homology to the acylase QuiP of Pseudomonas aeruginosa PAO1, demonstrating that it is at least partially responsible for the AHL-acylase activity. The recombinant enzyme, which was named auto-inducer inhibitor from Cyanobacteria (AiiC), shows broad acyl-chain length specificity. Because the presence of AHLs in the biomass of nitrogen-fixing cultures of Anabaena sp. PCC 7120 has been described recently, AiiC could represent a self-modulatory system to control the response to its own QS signals but could also be involved in the interference of signalling within complex microbial communities in which Cyanobacteria are present.

High-intensity narrow-spectrum light inactivation and wavelength sensitivity of Staphylococcus aureus.

Abstract: This study was conducted to investigate the bactericidal effects of visible light on methicillin-sensitive and methicillin-resistant Staphylococcus aureus (MRSA), and subsequently identify the wavelength sensitivity of S. aureus, in order to establish the wavelengths inducing maximum inactivation. Staphylococcus aureus, including MRSA strains, were shown to be inactivated by exposure to high-intensity visible light, and, more specifically, through a series of studies using a xenon broadband white-light source in conjunction with a selection of optical filters, it was found that inactivation of S. aureus occurs upon exposure to blue light of wavelengths between 400 and 420 nm, with maximum inactivation occurring at 405+/-5 nm. This visible-light inactivation was achieved without the addition of exogenous photosensitisers. The significant safety benefit of these blue-light wavelengths over UV light, in addition to their ability to inactivate medically important microorganisms such as MRSA, emphasises the potential of exploiting these non-UV wavelengths for disinfection applications.

Fungi and ionizing radiation from radionuclides

Abstract: Radionuclides in the environment are one of the major concerns to human health and ecotoxicology. The explosion at the Chernobyl nuclear power plant renewed interest in the role played by fungi in mediating radionuclide movement in ecosystems. As a result of these studies, our knowledge of the importance of fungi, especially in their mycorrhizal habit, in long-term accumulation of radionuclides, transfer up the food chain and regulation of accumulation by their host plants was increased. Micro-fungi have been found to be highly resilient to exposure to ionizing radiation, with fungi having been isolated from within and around the Chernobyl plant. Radioresistance of some fungal species has been linked to the presence of melanin, which has been shown to have emerging properties of acting as an energy transporter for metabolism and has been implicated in enhancing hyphal growth and directed growth of sensitized hyphae towards sources of radiation. Using this recently acquired knowledge, we may be in a better position to suggest the use of fungi in bioremediation of radioactively contaminated sites and cleanup of industrial effluent.

Transcription factors in fungi.

Abstract: Transcription factors (TFs) orchestrate gene expression control of a cell and, in many respects, their repertoire determines the life and functionality of the cell. For a better understanding of their regulatory mechanisms, it is essential to know the entire repertoire of TFs of a species. The increasing number of sequenced genomes together with the development of computational methods allow us not only to predict whole sets of TFs but also to analyse and compare them. Such an analysis is required in particular for fungal species, as our knowledge of the potential set of TFs in fungi is very limited. In fact, at present we do not know which TFs can in general be found in fungi, and which of them are strictly fungal specific. Other interesting questions regard the evolutionary relationships of fungal TFs with other kingdoms and the functions of fungal-specific TFs. This minireview addresses these issues. The analysis of predicted occurrences of DNA-binding domains in 62 fungal genomes reveals a set of 37 potential 'fungal' TF families. Six families are fungal-specific, i.e. they do not appear in other kingdoms. Interestingly, the fungal-specific TFs are not restricted to strictly fungal-specific functions. Consideration of fungal TF distributions in different kingdoms provides a platform to discuss the evolution of domains and TFs.

Induction of conidiation by endogenous volatile compounds in Trichoderma spp.

Abstract: Light and starvation are two principal environmental stimuli inducing conidiation in the soil micromycete Trichoderma spp. We observed that volatiles produced by conidiating colonies of Trichoderma spp. elicited conidiation in colonies that had not been induced previously by exposure to light. The inducing effect of volatiles was both intra- and interspecific. Chemical profiles of the volatile organic compounds (VOCs) produced by the nonconidiated colonies grown in the dark and by the conidiating colonies were compared using solid-phase microextraction of headspace samples followed by tandem GC-MS. The conidiation was accompanied by increased production of eight-carbon compounds 1-octen-3-ol and its analogs 3-octanol and 3-octanone. When vapors of these compounds were applied individually to dark-grown colonies, they elicited their conidiation already at submicromolar concentrations. It is concluded that the eight-carbon VOCs act as signaling molecules regulating development and mediating intercolony communication in Trichoderma.

Characterization of a gene encoding cellulase from uncultured soil bacteria

Abstract: To detect cellulases encoded by uncultured microorganisms, we constructed metagenomic libraries from Korean soil DNAs. Screenings of the libraries revealed a clone pCM2 that uses carboxymethyl cellulose (CMC) as a sole carbon source. Further analysis of the insert showed two consecutive ORFs ( celM2 and xynM2 ) encoding proteins of 226 and 662 amino acids, respectively. A multiple sequence analysis with the deduced amino acid sequences of celM2 showed 36% sequence identity with cellulase from the Synechococcus sp., while xynM2 had 59% identity to endo-1,4-β-xylanase A from Cellulomonas pachnodae . The highest enzymatic CMC hydrolysis was observable at pH 4.0 and 45 °C with recombinant CelM2 protein. Although the enzyme CelM2 additionally hydrolyzed avicel and xylan, no substrate hydrolysis was observed on oligosaccharides such as cellobiose, p NP-β - cellobioside, p NP-β-glucoside, and p NP-β-xyloside. These results showed that CelM2 is a novel endo-type cellulase.

Biofilm formation and interactions of bacterial strains found in wastewater treatment systems.

Abstract: Biofilm formation and adherence properties of 13 bacterial strains commonly found in wastewater treatment systems were studied in pure and mixed cultures using a crystal violet microtiter plate assay. Four different culture media were used, wastewater, acetate medium, glucose medium and diluted nutrient broth. The medium composition strongly affected biofilm formation. All strains were able to form pure culture biofilms within 24 h in at least one of the tested culture media and three strains were able to form biofilm in all four culture media, namely Acinetobacter calcoaceticus ATCC 23055, Comamonas denitrificans 123 and Pseudomonas aeruginosa MBL 0199. The adherence properties assessed were initial adherence, cell surface hydrophobicity, and production of amyloid fibers and extracellular polymeric substances. The growth of dual-strain biofilms showed that five organisms formed biofilm with all 13 strains while seven formed no or only weak biofilm when cocultured. In dual-strain cultures, strains with different properties were able to complement each other, giving synergistic effects. Strongest biofilm formation was observed when a mixture of all 13 bacteria were grown together. These results on attachment and biofilm formation can serve as a tool for the design of tailored systems for the degradation of municipal and industrial wastewater.

Dissecting the roles of Escherichia coli hydrogenases in biohydrogen production

Abstract: Escherichia coli can perform at least two modes of anaerobic hydrogen metabolism and expresses at least two types of hydrogenase activity. Respiratory hydrogen oxidation is catalysed by two ‘uptake’ hydrogenase isoenzymes, hydrogenase -1 and -2 (Hyd-1 and -2), and fermentative hydrogen production is catalysed by Hyd-3. Harnessing and enhancing the metabolic capability of E. coli to perform anaerobic mixed-acid fermentation is therefore an attractive approach for bio-hydrogen production from sugars. In this work, the effects of genetic modification of the genes encoding the uptake hydrogenases, as well as the importance of preculture conditions, on hydrogen production and fermentation balance were examined. In suspensions of resting cells pregrown aerobically with formate, deletions in Hyd-3 abolished hydrogen production, whereas the deletion of both uptake hydrogenases improved hydrogen production by 37% over the parent strain. Under fermentative conditions, respiratory H2 uptake activity was absent in strains lacking Hyd-2. The effect of a deletion in hycA on H2 production was found to be dependent upon environmental conditions, but H2 uptake was not significantly affected by this mutation.

The fungal pattern recognition receptor, Dectin‐1, and the associated cluster of C‐type lectin‐like receptors

Abstract: The mammalian natural killer gene complex (NKC) contains several families of type II transmembrane C-type lectin-like receptors (CLRs) that are best known for their involvement in the detection of virally infected or transformed cells, through the recognition of endogenous (or self) proteinacious ligands. However, certain CLR families within the NKC, particularly those expressed by myeloid cells, recognize structurally diverse ligands and perform a variety of other immune and homoeostatic functions. One such family is the ‘Dectin-1 cluster’ of CLRs, which includes MICL, CLEC-2, CLEC12B, CLEC9A, CLEC-1, Dectin-1 and LOX-1. Here, we review each of these CLRs, exploring our current understanding of their ligands and functions and highlighting where they have provided new insights into the underlying mechanisms of immunity and homeostasis.

Dimorphism in fungal plant pathogens

Abstract: Fungi are mostly sessile organisms, and thus have evolved ways to cope with environmental changes. Many fungi produce 'dormant' structures, which allow them to survive periods of unfavorable conditions. Another ingenious active approach to a changing environment has been adopted by the 'dimorphic fungi', which simply shift their thallic organization as a way to adapt and thrive in the new conditions. Dimorphism is extensively exploited by both plant and animal pathogenic fungi, where the encounter with the host prompts a shift in the mode of growth. In this review, we focus on the phenomenon of dimorphism among plant pathogenic fungi through discussion of several relatively well-studied exemplar species.