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At least 397 records · Page 22Linked to original sources
PubMed2003

Microbial transformation of metals and metalloids.

Throughout evolution, microbes have developed the ability to live in nearly every environmental condition on earth. They can grow with or without oxygen or light. Microbes can dissolve or precipitate ores and are able to yield energy from the reduction/oxidation of metal ions. Their metabolism depends on the availability of metal ions in essential amounts and protects itself from toxic amounts of metals by detoxification processes. Metals are metabolised to metallorgano-compounds, bound to proteins or used as catalytic centres of enzymes in biological reactions. Microbes, as every other cell, have developed a whole range of mechanisms for the uptake and excretion of metals and their metabolised compounds. The diversity of microbial metabolism can be illustrated by the fact that certain microbes can be found living on arsenate, which is considered a highly toxic metal for most other forms of live.

Catalysis↗
PubMed2003

Minimal model for genome evolution and growth.

Textual analysis of typical microbial genomes reveals that they have the statistical characteristics of a DNA sequence of a much shorter length. This peculiar property supports an evolutionary model in which a genome evolves by random mutation but primarily grows by random segmental duplication. That genomes grew mostly by duplication is consistent with the observation that repeat sequences in all genomes are widespread and intragenomic and intergenomic homologous genes are preponderant across all life forms.

DNA, Bacterial↗
PubMed2007

What can microbial genetics teach sociobiology?

Progress in our understanding of sociobiology has occurred with little knowledge of the genetic mechanisms that underlie social traits. However, several recent studies have described microbial genes that affect social traits, thereby bringing genetics to sociobiology. A key finding is that simple genetic changes can have marked social consequences, and mutations that affect cheating and recognition behaviors have been discovered. The study of these mutants confirms a central theoretical prediction of social evolution: that genetic relatedness promotes cooperation. Microbial genetics also provides an important new perspective: that the genome-to-phenome mapping of social organisms might be organized to constrain the evolution of social cheaters. This constraint can occur both through pleiotropic genes that link cheating to a personal cost and through the existence of phoenix genes, which rescue cooperative systems from selfish and destructive strategies. These new insights show the power of studying microorganisms to improve our understanding of the evolution of cooperation.

Animals↗
PubMed2001

Predicting the emergence of resistance to antifungal drugs.

The emergence of antifungal drug resistance is inevitable. Here I discuss antibiotic resistance in the context of the adaptive potential of fungi and I propose an approach to predicting the evolution of antifungal resistance using experimental evolution of DNA sequences and microbial populations. Prediction is based on determination of evolutionary potential at two levels, the gene and the genome. At the level of the gene, evolutionary potential depends on the sequence space of candidate resistance genes defined by the fitness effects of all possible mutations in all possible combinations. At the level of the genome, evolutionary potential depends on the adaptive landscape defined by the fitness effects of all possible interactions among alleles constituting the genotype.

Antifungal Agents↗
PubMed1998

The renaissance of microbiology.

Microbiology is finally occupying its true position as the pre-eminent field in life sciences. This is due to advances in molecular techniques that confirm the evolutionary significance of the biology of microbes. It is anticipated that the use of comparative genomics will provide information that will advance the understanding of mechanisms of pathogenesis and the importance of secondary metabolism in social microbiology. More emphasis on studies of microbial diversity will increase its value in both fundamental microbiology and its industrial applications.

Biological Evolution↗
PubMed2004

Microbial adaptation and change: avian influenza.

The evolution of influenza is a continuing process involving viral and host factors. The increasing frequency of emergence of the highly pathogenic H5N1, H7N3 and H7N7 influenza viruses and the panzootic spread of H9N2 influenza virus, all of which can be potentially transmitted to humans, are of great concern to both veterinary and human public health officials. The question is how soon the next pandemic will emerge. A convergence of factors, including the population densities of poultry, pigs and humans, are likely factors affecting the evolution of the virus. Highly concentrated poultry and pig farming, in conjunction with traditional live animal or 'wet' markets, provide optimal conditions for increased mutation, reassortment and recombination of influenza viruses. Strategies to reduce the evolution of influenza and the emergence of pandemics include the separation of species, increased biosecurity, the development of new vaccine strategies and better basic knowledge of the virus. More effective co-operation between scientists and veterinary and public health officials is required to achieve these goals.

Animals↗
PubMed2002

Big effects from small changes: possible ways to explore nature's chemical diversity.

Fungi or bacteria that produce secondary metabolites often have the potential to bring up various compounds from a single strain. The molecular basis for this well-known observation was confirmed in the last few years by several sequencing projects of different microorganisms. Besides well-known examples about induction of a selected biosynthesis (for example, by high- or low-phosphate cultivation media), no overview about the potential in this field for finding natural products was given. We have investigated the systematic alteration of easily accessible cultivation parameters (for example, media composition, aeration, culture vessel, addition of enzyme inhibitors) in order to increase the number of secondary metabolites available from one microbial source. We termed this way of revealing nature's chemical diversity the 'OSMAC (One Strain-Many Compounds) approach' and by using it we were able to isolate up to 20 different metabolites in yields up to 2.6 g L(-1) from a single organism. These compounds cover nearly all major natural product families, and in some cases the high production titer opens new possibilities for semisynthetic methods to enhance even more the chemical diversity of selected compounds. The OSMAC approach offers a good alternative to industrial high-throughput screening that focuses on the active principle in a distinct bioassay. In consequence, the detection of additional compounds that might be of interest as lead structures in further bioassays is impossible and clearly demonstrates the deficiency of the industrial procedure. Furthermore, our approach seems to be a useful tool to detect those metabolites that are postulated to be the final products of an amazing number of typical secondary metabolite gene clusters identified in several microorganisms. If one assumes a (more or less) defined reservoir of genetic possibilities for several biosynthetic pathways in one strain that is used for a highly flexible production of secondary metabolites depending on the environment, the OSMAC approach might give more insight into the role of secondary metabolism in the microbial community or during the evolution of life itself.

Actinobacteria↗
PubMed1980

Anabolic-catabolic glucose utilization and product formation of Streptomyces griseus.

If in stationary growth phases appearing in the submerged cultivation of Streptomyces griseus several times the consumption rates of glucose and oxygen and the rates of streptomycin formation are put in relation, the following results are obtained: The yield coefficient Ysp of glucose was below 0.1. Since from the stoichiometric equation of turnover for the biosynthesis of the streptomycin follows that the substrate and the product are in the same weight relation, it was possible to check whether the quantity of glucose that does not appear in the streptomycin is used for the energy supplying synthesis or conservation reactions. As a characteristic value was built up the quotient qo3/qgluc that in total substrate oxidations takes the numerical value 6. This quotient varied between 2.0 and 6.0 so that anabolic side reactions during the production of secondary substances were concluded from. As possibilities are discussed syntheses of analytically disregarded primary metabolites or preliminary steps of the biosynthesis of streptomycin. Due to the decrease of the enthalpy production by anabolic reaction steps in stationary growth phases follows a physiological-energetical importance of microbial product syntheses with likely evolutive action.

Culture Media↗
PubMed1999

Bacteria designed for bioremediation.

Although many environmental pollutants are efficiently degraded by microorganisms, others persist and constitute a severe health hazard. In some instances, persistence is a consequence of the inadequate catabolic potential of the available microorganisms. Gene technology, combined with a solid knowledge of catabolic pathways and microbial physiology, enables the experimental evolution of new or improved catabolic activities for such pollutants.

Bacteria↗
PubMed2000

Effect of Cd-containing wood ash on the microflora of coniferous forest humus.

The use of wood ash in forestry has been questioned because the cadmium (Cd) concentration of ash, which varies between 1 and 20 mg kg(-1) ash, exceeds the level allowed for fertilizers (3 mg kg(-1)) used in agriculture. To investigate the combined and separated effects of Cd and ash on the forest humus microflora, pumice or wood ash, spiked with a water-soluble (CdCl(2)) or -insoluble (CdO) form of Cd at three levels (0, 400 and 1000 mg kg(-1)), were applied at a fertilization level of 5000 kg ha(-1) in a laboratory microcosm study. The trial consisted of 60 microcosms (five replications per treatment), which were incubated in darkness at +20 degrees C and a constant relative air humidity of 60%. After two months the humus in the microcosms was sampled. Analyses of CO(2) evolution to measure the overall microbial activity and of phospholipid fatty acid (PLFA) pattern to measure microbial community structure were performed. The substrate-use patterns of Biolog EcoPlates were analyzed as a measure of bacterial functionality. Finally the bacterial (3)H-thymidine incorporation in the presence of different concentrations of Cd and the number of colony forming units (cfu) of bacteria on nutrient agar in the presence of 0, 5 and 20 mg Cd l(-1) agar were applied to measure Cd tolerance. The use of pumice (pH of humus under the pumice 4.0) did not induce any changes in the above variables compared to two untreated microcosms (humus pH 3.9). Pumice was therefore used to distribute the Cd evenly over the humus surface in order to estimate the possible effect of Cd without ash (pH of humus under the ash 7.0). The application of ash increased the microbial activity, changed the PLFA and substrate-use patterns and increased cfu compared to the humus under pumice. The form and level of Cd in the ash had no further effect on this result. In the humus under pumice the level, but not the form of Cd decreased the microbial activity and changed the PLFA pattern compared to the unspiked pumice. None of the treatments induced bacterial tolerance to Cd. Ash thus protected the humus microflora from the harmful effects of Cd.

Journal Article↗
PubMed1999

Molecular diversity and evolutionary relationships of Tn1546-like elements in enterococci from humans and animals.

We report on a detailed study on the molecular diversity and evolutionary relationships of Tn1546-like elements in vancomycin-resistant enterococci (VRE) from humans and animals. Restriction fragment length polymorphism (RFLP) analysis of the VanA transposon of 97 VRE revealed seven different Tn1546 types. Subsequent sequencing of the complete VanA transposons of 13 VRE isolates representing the seven RFLP types followed by sequencing of the identified polymorphic regions in 84 other VanA transposons resulted in the identification of 22 different Tn1546 derivatives. Differences between the Tn1546 types included point mutations in orf1, vanS, vanA, vanX, and vanY. Moreover, insertions of an IS1216V-IS3-like element in orf1, of IS1251 in the vanS-vanH intergenic region, and of IS1216V in the vanX-vanY intergenic region were found. The presence of insertion sequence elements was often associated with deletions in Tn1546. Identical Tn1546 types were found among isolates from humans and farm animals in The Netherlands, suggesting the sharing of a common vancomycin resistance gene pool. Application of the genetic analysis of Tn1546 to VRE isolates causing infections in Hospitals in Oxford, United Kingdom, and Chicago, Ill., suggested the possibility of the horizontal transmission of the vancomycin resistance transposon. The genetic diversity in Tn1546 combined with epidemiological data suggest that the DNA polymorphism among Tn1546 variants can successfully be exploited for the tracing of the routes of transmission of vancomycin resistance genes.

Animals↗
PubMed2002

Comparative genomic analysis of archaeal genotypic variants in a single population and in two different oceanic provinces.

Planktonic crenarchaeotes are present in high abundance in Antarctic winter surface waters, and they also make up a large proportion of total cell numbers throughout deep ocean waters. To better characterize these uncultivated marine crenarchaeotes, we analyzed large genome fragments from individuals recovered from a single Antarctic picoplankton population and compared them to those from a representative obtained from deeper waters of the temperate North Pacific. Sequencing and analysis of the entire DNA insert from one Antarctic marine archaeon (fosmid 74A4) revealed differences in genome structure and content between Antarctic surface water and temperate deepwater archaea. Analysis of the predicted gene products encoded by the 74A4 sequence and those derived from a temperate, deepwater planktonic crenarchaeote (fosmid 4B7) revealed many typical archaeal proteins but also several proteins that so far have not been detected in archaea. The unique fraction of marine archaeal genes included, among others, those for a predicted RNA-binding protein of the bacterial cold shock family and a eukaryote-type Zn finger protein. Comparison of closely related archaea originating from a single population revealed significant genomic divergence that was not evident from 16S rRNA sequence variation. The data suggest that considerable functional diversity may exist within single populations of coexisting microbial strains, even those with identical 16S rRNA sequences. Our results also demonstrate that genomic approaches can provide high-resolution information relevant to microbial population genetics, ecology, and evolution, even for microbes that have not yet been cultivated.

Amino Acid Sequence↗
PubMed2003

In vivo lysogenic conversion of Tox(-) Streptococcus pyogenes to Tox(+) with Lysogenic Streptococci or free phage.

Temperate bacteriophage can transfer toxin-encoding genes between bacteria, often resulting in acquired pathogenicity. However, little is known regarding the effects of the eukaryotic host on the phage-pathogen interaction. Using Streptococcus pyogenes as a model, we demonstrate, both in vitro and in vivo, that the eukaryote mediates the efficient induction of toxin-encoding temperate phage and the resultant conversion of Tox(-) flora to Tox(+). Furthermore, we show that both phage induction and subsequent conversion need not happen in the same mammalian host, as host-to-host phage transmission can result in toxigenic conversion within the secondary host. Ultimately, our findings demonstrate that the eukaryotic host serves as an essential component in the phage-mediated evolution of virulence within the microbial population.

Animals↗
PubMed2005

Probiotics: an emerging therapy.

There is considerable clinical interest in the utility of probiotic therapy--the feeding of (live) non-pathogenic bacteria, originally derived from the alimentary tract, for disease treatment or health promotion. The microflora of the gastrointestinal tract is essential for mucosal protection, for immune education and for metabolism of fecal residue. Physiological disturbances of these processes, when they occur, result from: i) alteration of a microbial ecosystem, originally conserved by evolution; ii) reduced consumption of microorganisms; iii) invasion of pathogens; or iv) modern interventions. Recent data support the use of proven probiotic organisms in prevention and treatment of flora-related gastrointestinal disorders including inflammatory bowel disease, infectious and antibiotic related diarrheas, and post-resection disorders including pouchitis. Therapeutic activity of probiotic bacteria can be due to competition with pathogens for nutrients and mucosal adherence, production of antimicrobial substances, and modulation of mucosal immune functions. Although a promising treatment, controlled clinical trials are necessary to validate the benefit of probiotics.

Animals↗
PubMed2006

Microbial diversity in the deep sea and the underexplored "rare biosphere".

The evolution of marine microbes over billions of years predicts that the composition of microbial communities should be much greater than the published estimates of a few thousand distinct kinds of microbes per liter of seawater. By adopting a massively parallel tag sequencing strategy, we show that bacterial communities of deep water masses of the North Atlantic and diffuse flow hydrothermal vents are one to two orders of magnitude more complex than previously reported for any microbial environment. A relatively small number of different populations dominate all samples, but thousands of low-abundance populations account for most of the observed phylogenetic diversity. This "rare biosphere" is very ancient and may represent a nearly inexhaustible source of genomic innovation. Members of the rare biosphere are highly divergent from each other and, at different times in earth's history, may have had a profound impact on shaping planetary processes.

Biodiversity↗
PubMed1979

Cultivation requirements for Treponema pallidum, Mycobacterium leprae and other microbial and mammalian microaerophilic cells.

Atmospheric and biological evolution progressed simultaneously and today certain cell types flourish only at oxygen tensions which were ambient 600 million years ago, i.e., at 5 to 10 mm Hg. In man, a continuous oxygen flow at these pressures is supplied in the skin where Treponema pallidum, Mycobacterium leprae and members of the genus Rickettsia grow best. In vitro studies support the microaerophilic status of these organisms and of certain other microbial and mammalian cells. Vigorous growth in pure culture will await the development of techniques which can maintain these low oxygen tensions at the cell walls of the microbes as they replicate and consume increasing amounts of oxygen. Continuing failure to consistently isolate microbes from active lesions in patients with rheumatoid arthritis or systemic lupus erythematosus may reflect the universal absence of suitable methods for isolation of microaerophilic microbes.

Anaerobiosis↗
PubMed2002

Chemical warfare between microbes promotes biodiversity.

Evolutionary processes generating biodiversity and ecological mechanisms maintaining biodiversity seem to be diverse themselves. Conventional explanations of biodiversity such as niche differentiation, density-dependent predation pressure, or habitat heterogeneity seem satisfactory to explain diversity in communities of macrobial organisms such as higher plants and animals. For a long time the often high diversity among microscopic organisms in seemingly uniform environments, the famous "paradox of the plankton," has been difficult to understand. The biodiversity in bacterial communities has been shown to be sometimes orders of magnitudes higher than the diversity of known macrobial systems. Based on a spatially explicit game theoretical model with multiply cyclic dominance structures, we suggest that antibiotic interactions within microbial communities may be very effective in maintaining diversity.

Anti-Bacterial Agents↗