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At least 613 records · Page 34Linked to original sources
PubMed1996

[Effects of different procedures of disinfection on the bacteriologic quality of hemodialysis monitors of the Cobe CS3 and AK 100 type].

]n recent years, hemodialysis treatment for chronic renal failure has been increasing. Although the technical evolutions have improved the therapy, the problem of microbial, toxic and chemical contamination of the dialysis fluid is now re-emerging. Most of all, because of increasing use of high-flux dialysis and its potential for transmembrane transport of bacteria into patients, one should be aware that dialysis fluid pathways may be colonised with bacteria. On the bacterial point of view, the French legislation proposed 100 CFU/mL as a maximum for total count of aerobic bacteria in the bi-osmosed water used for dilution of the dialysis concentrate. This study took place during 8 weeks in the children-hospital dialysis unit in Nancy (France). Our laboratory have succeeded in validating an aseptic bacteriological sampling procedure within fluid pathways of haemodialysis monitors Cobe CS3 and AK 100. It has also be shown that 6 to 12 hours of dialysis monitoring doesn't affect the quantitative and qualitative bacterial contamination of the biosmosed water (mean: 5 CFU/100 mL) drained through the 5 years' old internal pipes of the 2 monitors. So it has whatever the 4 different disinfection procedures applied and on the monitors (Formol or Formol + Citric acid + Chlorine or Heat or Heat + dehydrated Citric acid).

Child↗
PubMed1980

The influence of life on the evolution of the atmosphere.

The early history of life on earth may have been characterized by coevolution of microbial metabolism and atmospheric composition. Metabolic developments affected the composition of the atmosphere, and the resulting changes in the atmosphere stimulated the evolution of new metabolic capabilities. The first organisms eked out an existence by deriving energy from the fermentation of organic compounds abiotically synthesized. The abiotic source was meager, however, and when autotrophy arose, life was freed from its dependence on abiotic synthesis. The expanded level of biological activity made possible by autotrophy resulted in an increased rate of burial of reduced organic matter in sea floor sediments. The resultant drain on the concentration of electron donors in the biosphere caused a decline in the hydrogen content of the atmosphere. Biological productivity was limited by the supply of reduced compounds. This paper explores the biogeochemical circulation of electron donors in the primitive anaerobic ocean, concluding that their shortage was so critical as to provide strong selective pressure for the evolution of algal photosynthesis.

Anaerobiosis↗
PubMed2002

Microsporidia: biology and evolution of highly reduced intracellular parasites.

Microsporidia are a large group of microbial eukaryotes composed exclusively of obligate intracellular parasites of other eukaryotes. Almost 150 years of microsporidian research has led to a basic understanding of many aspects of microsporidian biology, especially their unique and highly specialized mode of infection, where the parasite enters its host through a projectile tube that is expelled at high velocity. Molecular biology and genomic studies on microsporidia have also drawn attention to many other unusual features, including a unique core carbon metabolism and genomes in the size range of bacteria. These seemingly simple parasites were once thought to be the most primitive eukaryotes; however, we now know from molecular phylogeny that they are highly specialized fungi. The fungal nature of microsporidia indicates that microsporidia have undergone severe selective reduction permeating every level of their biology: From cell structures to metabolism, and from genomics to gene structure, microsporidia are reduced.

Animals↗
PubMed1991

Draft results of a workshop to develop guidelines for studies involving microbial incidence or populations in the oral cavity.

The following five outlines are the results to date of the Workshop held in Rockville, Maryland, in January, 1990. The topics considered in these outlines are: (1) validation of immunological and/or nucleic acid identification probes, (2) cross-calibration of methods and/or laboratories for multi-laboratory cooperative studies, (3) choosing methods for identifying or describing microbial populations appropriate to the scientific question asked, (4) microbial ecology methods (e.g., population dynamics) for the oral cavity studies, and (5) epidemiological methods (e.g., incidence, risk factor analysis) for oral microbial studies. Each topic was considered by two independent groups of participants and later rationalized into one. These outlines are meant to be working outlines for evolution of a set of guidelines to advise on designing studies with microbial incidence and/or population components. We are publishing this preliminary version to elicit comment and criticism from people who did not attend the Workshop. (Attendance at the Workshop was necessarily limited by both space and funds). Some of the topic outlines have been condensed to save Journal space. The full document is available on request. The next stage will be an open forum to gather and discuss further amplification of the "Guidelines", planned for April 17, 1991, Acapulco, Mexico, in conjunction with the IADR/AADR Meeting. Written comments and requests for further information should be sent to the Workshop organizer (MIK) at the above address.(ABSTRACT TRUNCATED AT 250 WORDS)

DNA, Bacterial↗
PubMed1998

A stochastic model for the rapid emergence of specific vertebrate immunity incorporating horizontal transfer of systems enabling duplication and combinational diversification.

Recent molecular data indicate that the antigen-specific combinatorial immune response is restricted to jawed vertebrates where it is found in representatives of all class from cartilagenous fishes to mammals. Here, we analyse the relatively rapid emergence of the combinatorial system terms of three stochastic process, with the system reaching essentially full capacity in immunoglobulin recognition elements and diversification and recombination of gene segments in an evolutionary span of time of less than 20 million years. The mechanisms for inducibility were coopted from ancient and widely spread processes in phylogeny for regulation of cell division. The proposed process of formation entailed the evolution of unknown ancestral genes into those specifying bona fide immunoglobulin domains, and the generation of multiple copies of these via a series of events facilitated by horizontal transfer of site-specific recombinases and recombination signal sequences most probably from microbial and fungal sources. The second process is one of rapid "decay" (evolution) which occurred in about 10 million year under stringent selective conditions to generate proper conserved canonical sequences. The third process is that of the long term evolution of these characteristic immunoglobulin domains over the 450 million years since their emergence. As a first approximation the rates of these three processes were computed using first order differential equations. The rate of formation has a magnitude of 10-7 substitutions per site per year, and that of rapid modifications is 10-8 substitutions per site per year. The long term rate of immunoglobulin evolution is comparable to that of other moderately conserved proteins, (1-3) x 10-9 substitutions per site per year). This model is testable by searching for "footprints" of microbial and fungal DNA processing enzymes and recombination mechanisms. The hypothesis raises the general concept that horizontal transfer of genes facilitating rearrangement and duplication can catalyse major steps of macroevolution.

Animals↗
PubMed1998

Lindane degradation and effects on soil microbial activity.

The degradation of U-14C-lindane in two Egyptian soils was determined in a three-month laboratory incubation. Lindane mineralization was slow and limited in both soils. Evolution of 14CO2 increased with time but only reached 3.5 to 5.5% of the initial 14C-concentration within 90 days. At that time both soils contained about 88% of the applied radiocarbon; 33% to 37% of the initial dose was unextractable and assumed bound to the soils. The methanol-extractable 14C primarily contained lindane with traces of minor metabolites. Radiorespirometry was used to evaluate the effect of lindane on soil microbial activity. Low concentrations of the insecticide initially supressed 14CO2 evolution from U-14C-glucose and microbial activity was significantly inhibited by 10 mg lindane/kg soil.

Carbon Dioxide↗
PubMed2003

Biosurfactants: evolution and diversity in bacteria.

In summary, biosurfactants are an example of a class of microbial natural products that has coevolved among many genera. But whereas the biosurfactants produced in the bacterial and archaeal domains are convergent in function (suggesting that they are very important), they have developed in parallel with respect to genotype and phenotype (the surfactants are not related genetically or in terms of molecular structure). Because of this parallel evolution, currently available molecular screening techniques are of little use for the discovery of new biosurfactants. Development of such techniques will continue to be problematic because there is no relationship between the surfactants produced by different microbial genera and even species. Yet, the potential for application of biosurfactants and other natural products is great due to growing demand for biodegradable and environmentally friendly analogues for synthetic chemicals.

Archaea↗
PubMed2003

The importance of Bi-Digital O-Ring Test in the treatment of multiple hepatic abscesses: a case history.

The Bi-Digital O-Ring Test has been very useful in the identification of bacterial and viral infections, as well as other etiological agents, in difficult clinical cases. Case report of a patient with multiple hepatic abscesses (pylephlebitis induced hepatic abscess is the most difficult abscess to treat), in which the etiological agent was suggested through Bi-Digital O-Ring Test with excellent clinical evolution after modification of previously ineffective multi anti-microbial treatment is presented. 45 years old, female with a history of pain at right hypochondria for 15 days, with jaundice, oscillating fever and shivering. Computerized tomography showed liver with multiples nodules in the parenchyma with additional appendicitis. An appendectomy was performed with drainage of intra abdominal abscesses. Treatment with metronidazol, ceftazidim and amicacine was performed with no improvement while the general condition of the patient was deteriorating progressively in the following 3 weeks. Bi-Digital O-Ring Test was then performed to determine the etiological agent and the drug compatibility test among effective antimicrobial agents. Based on the Bi-Digital O-Ring Test, the main etiological agent was found to be Enterobacter aerogenes. Amongst the three antibiotics that were being used, only metronidazol was effective and the other 2 was cancelled its effect. Based on Bi-Digital O-Ring Test findings two new antibiotics (cefadroxil and imipenen), were added to metronidazol and additional cilantro tablets by Hayashibara, Japan was given, and Selective Drug Uptake Enhancement Method performed, with excellent clinical, laboratory testing and tomography improvement within 10 days. Bi-Digital O-Ring Test suggested the etiological agent, and effective and mutually compatible antibiotics for treating the abscesses which resulted in a good clinical evolution, characterized by relief of fever and reduction of the hepatic abscesses in a short period and followed complete disappearance of hepatic abscess.

Anti-Bacterial Agents↗
PubMed2006

The next generation of microarray research: applications in evolutionary and ecological genomics.

Microarray technology is one of the key developments in recent years that has propelled biological research into the post-genomic era. With the ability to assay thousands to millions of features at the same time, microarray technology has fundamentally changed how biological questions are addressed, from examining one or a few genes to a collection of genes or the whole genome. This technology has much to offer in the study of genome evolution. After a brief introduction on the technology itself, we then focus on the use of microarrays to examine genome dynamics, to uncover novel functional elements in genomes, to unravel the evolution of regulatory networks, to identify genes important for behavioral and phenotypic plasticity, and to determine microbial community diversity in environmental samples. Although there are still practical issues in using microarrays, they will be alleviated by rapid advances in array technology and analysis methods, the availability of many genome sequences of closely related species and flexibility in array design. It is anticipated that the application of microarray technology will continue to better our understanding of evolution and ecology through the examination of individuals, populations, closely related species or whole microbial communities.

Ecology↗
PubMed1995

Effect of carbon:nitrogen ratio on kinetics of phenol biodegradation by Acinetobacter johnsonii in saturated sand.

In polluted soil or ground water, inorganic nutrients such as nitrogen may be limiting, so that Monod kinetics for carbon limitation may not describe microbial growth and contaminant biodegradation rates. To test this hypothesis we measured 14CO2 evolved by a pure culture of Acinetobacter johnsonii degrading 120 micrograms 14C-phenol per ml in saturated sand with molar carbon:nitrogen (CN) ratios ranging from 1.5 to 560. We fit kinetics models to the data using non-linear least squares regression. Phenol disappearance and population growth were also measured at CN1.5 and CN560. After a 5- to 10-hour lag period, most of the 14CO2 evolution curves at all CN ratios displayed a sigmoidal shape, suggesting that the microbial populations grew. As CN ratio increased, the initial rate of 14CO2 evolution decreased. Cell growth and phenol consumption occurred at both CN1.5 and CN560, and showed the same trends as the 14CO2 data. A kinetics model assuming population growth limited by a single substrate best fit the 14CO2 evolution data for CN1.5. At intermediate to high CN ratios, the data were best fit by a model originally formulated to describe no-growth metabolism of one substrate coupled with microbial growth on a second substrate. We suggest that this dual-substrate model describes linear growth on phenol while nitrogen is available and first-order metabolism of phenol without growth after nitrogen is depleted.

Acinetobacter↗
PubMed1998

Antibiotic-selective environments.

The evolution and spread of antibiotic resistance depends on the antibiotic pressure exerted in the microbial environment. Selective effects occur in selective compartments, where particular antibiotic concentrations result in a differential growth rate of resistant bacterial variants. This may happen even at very low antibiotic concentrations able to select low-level-resistant bacteria. When more than one antibiotic is present in the environment, the multiple and fluctuating pressure produces the selection of bacterial variants that use multiple or multipurpose mechanisms or optimize a single mechanism of resistance to survive under the variable environmental conditions. Host factors such as immunity contribute to the selective process. Antibiotics themselves may promote bacterial diversity, either mediated by the random drift effect or triggering the increase of mutational events under bacterial stress. Analysis of selective environment-related antibiotic-host-bacteria interactions is essential to understanding the biology of antibiotic resistance.

Adaptation, Physiological↗
PubMed2006

Evolution of soil organic matter changes using pyrolysis and metabolic indices: a comparison between organic and mineral fertilization.

The aim of this study was to evaluate chemical and biochemical changes of organic matter in fertilized (ammonium nitrate) and amended (vermicompost and manure) soils using pyrolysis and metabolic indices. The metabolic potential [dehydrogenase (DH-ase)/water soluble organic carbon (WSOC)], the metabolic quotient (qCO2) and the microbial quotient (Cmic:Corg) were calculated as indices of soil organic matter evolution. Pyrolysis-gas chromatography (Py-GC) was used to study structural changes in the organic matter. Carbon forms and microbial biomass have been measured by dichromate oxidation and fumigation-extraction methods, respectively. Dehydrogenase activity has been tested using INT (p-Iodonitrotetrazolium violet) as substrate. The results showed that organic amendment increased soil microbial biomass and its activity which were strictly related to pyrolytic mineralization and humification indices (N/O, B/E3). Mineral fertilization caused a greater alteration of native soil organic matter than the organic amendments, in that a high release of WSOC and relatively large amounts of aliphatic pyrolytic products, were observed. Therefore, the pyrolysis and metabolic indices provided similar and complementary information on soil organic matter changes after mineral and organic fertilization.

Biomass↗
PubMed2000

Vaginal bacterial microflora modifications during the growth of healthy cows.

The aim of this work was first, to determine the predominant groups capable of colonizing the vagina and maintaining high numbers with time. The normal microbial flora of the cow's vagina and its evolution from weaning to service was then studied using standard microbiological methods. The results show that the most dominant bacteria belong to the streptococci, followed by the staphylococci, with similar levels during the whole study period. Enterobacteriaceae and lactobacilli were present at very low levels, the latter increasing during the cow's growth, suggesting some kind of hormonal influence. The results will allow the selection of micro-organisms with probiotic characteristics, classified as GRAS (Generally Regarded as Safe), to be used in the prevention of infections in the vaginal tract of cows, such as metritis, which produces delayed periods between partum and conception, and consequent economic losses.

Animals↗
PubMed1998

Paradoxical enhancement of the activity of a bacterial multidrug transporter caused by substitutions of a conserved residue.

Substitution of threonine or serine for the evolutionary conserved intramembrane proline P347 of the Bacillus subtilis multidrug transporter Bmr significantly increases the toxin-effluxing activity of Bmr without affecting its abundance in the cell. In cocultivation experiments, we demonstrate that although the mutant T347 Bmr is advantageous to cells growing in the presence of a toxin, the wild-type P347 Bmr is advantageous under the conditions of nutritional limitation. This may explain why Bmr has evolved the way it did, that is, with proline at position 347. These observations provide a basis for speculating that the evolution of Bmr has been determined by its presently unidentified natural function rather than by its ability to expel diverse toxins from the cell.

Acriflavine↗
PubMed2000

Compensatory mutations, antibiotic resistance and the population genetics of adaptive evolution in bacteria.

In the absence of the selecting drugs, chromosomal mutations for resistance to antibiotics and other chemotheraputic agents commonly engender a cost in the fitness of microorganisms. Recent in vivo and in vitro experimental studies of the adaptation to these "costs of resistance" in Escherichia coli, HIV, and Salmonella typhimurium found that evolution in the absence of these drugs commonly results in the ascent of mutations that ameliorate these costs, rather than higher-fitness, drug-sensitive revertants. To ascertain the conditions under which this compensatory evolution, rather than reversion, will occur, we did computer simulations, in vitro experiments, and DNA sequencing studies with low-fitness rpsL (streptomycin-resistant) mutants of E. coli with and without mutations that compensate for the fitness costs of these ribosomal protein mutations. The results of our investigation support the hypothesis that in these experiments, the ascent of intermediate-fitness compensatory mutants, rather than high-fitness revertants, can be attributed to higher rates of compensatory mutations relative to that of reversion and to the numerical bottlenecks associated with serial passage. We argue that these bottlenecks are intrinsic to the population dynamics of parasitic and commensal microbes and discuss the implications of these results to the problem of drug resistance and adaptive evolution in parasitic and commmensal microorganisms in general.

Adaptation, Biological↗
PubMed2005

The net of life: reconstructing the microbial phylogenetic network.

It has previously been suggested that the phylogeny of microbial species might be better described as a network containing vertical and horizontal gene transfer (HGT) events. Yet, all phylogenetic reconstructions so far have presented microbial trees rather than networks. Here, we present a first attempt to reconstruct such an evolutionary network, which we term the "net of life". We use available tree reconstruction methods to infer vertical inheritance, and use an ancestral state inference algorithm to map HGT events on the tree. We also describe a weighting scheme used to estimate the number of genes exchanged between pairs of organisms. We demonstrate that vertical inheritance constitutes the bulk of gene transfer on the tree of life. We term the bulk of horizontal gene flow between tree nodes as "vines", and demonstrate that multiple but mostly tiny vines interconnect the tree. Our results strongly suggest that the HGT network is a scale-free graph, a finding with important implications for genome evolution. We propose that genes might propagate extremely rapidly across microbial species through the HGT network, using certain organisms as hubs.

Algorithms↗
PubMed2026

Host-driven evolution shapes the polysaccharide utilization profiles of alga-associated Flavobacteriaceae.

BACKGROUND: Marine algae represent major producers of complex polysaccharides and serve as hosts for diverse microbial communities in the phycosphere. Flavobacteriaceae are among the key bacterial taxa involved in polysaccharide degradation and carbon remineralization in this environment. However, the extent to which algal hosts drive the divergence of polysaccharide utilization profiles in these bacteria remains unclear. RESULTS: We conducted a genome-resolved analysis of 103 cultured Flavobacteriaceae strains isolated from red, green, and brown macroalgae, as well as from diatoms and dinoflagellates. We found that macroalga-associated strains generally harbored more abundant and diverse CAZyme-encoding genes than their microalga-associated counterparts. Moreover, strains associated with different algal phyla showed distinct metabolic specializations that aligned with the typical polysaccharides of their respective hosts, strongly supporting host-specific adaptation. In four widely distributed genera (Maribacter, Flagellimonas, Polaribacter, Winogradskyella), CAZyme profile dissimilarity and key glycoside hydrolase gene divergence exhibited phylogenetic congruence with algal host phylogeny (Mantel r up to 0.76 and 0.85, respectively), indicative of host-associated functional adaptation. Using Maribacter as a model, cultivation experiments and transcriptome characterization demonstrated that polysaccharide utilization efficiency is not solely linked to the organization of genes into polysaccharide utilization loci (PULs), but also associated with the expression dynamics of key transcription factors (TFs), particularly those from AraC and DeoR families, whose expression patterns were coordinated with laminarin degradation. Notably, these two TF families also exhibited host-associated divergence patterns similar to those of CAZyme-encoding genes. Furthermore, analysis of the Tara Oceans metagenomic data indicated that, within the AraC and DeoR families, a higher proportion of genes were positively correlated with chlorophyll a content compared to other TF families, reinforcing their specialized roles in alga-associated bacterial lifestyles. CONCLUSIONS: Our integrative genomic and transcriptomic analyses reveal evolutionary and regulatory adaptation of marine Flavobacteriaceae to distinct algal hosts. These findings highlight algae-derived habitats as specialized niches that shape microbial metabolic potential, and suggest that carbohydrate metabolism plays a key role in host-driven bacterial evolution across global oceans. Video Abstract.

Flavobacteriaceae↗