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PubMed2006

DNA secretion and gene-level selection in bacteria.

Natural genetic transformation can facilitate gene transfer in many genera of bacteria and requires the presence of extracellular DNA. Although cell lysis can contribute to this extracellular DNA pool, several studies have suggested that the secretion of DNA from living bacteria may also provide genetic material for transformation. This paper reviews the evidence for specific secretion of DNA from intact bacteria into the extracellular environment and examines this behaviour from a population-genetics perspective. A mathematical model demonstrates that the joint action of DNA secretion and transformation creates a novel type of gene-level natural selection. This model demonstrates that gene-level selection could explain the existence of DNA secretion mechanisms that provide no benefit to individual cells or populations of bacteria. Additionally, the model predicts that any trait affecting DNA secretion will experience selection at the gene level in a transforming population. This analysis confirms that the secretion of DNA from intact bacterial cells is fully explicable with evolutionary theory, and reveals a novel mechanism for bacterial evolution.

Bacteria↗
PubMed1995

Characterization of muconate and chloromuconate cycloisomerase from Rhodococcus erythropolis 1CP: indications for functionally convergent evolution among bacterial cycloisomerases.

Muconate cycloisomerase (EC 5.5.1.1) and chloromuconate cycloisomerase (EC 5.5.1.7) were purified from extracts of Rhodococcus erythropolis 1CP cells grown with benzoate or 4-chlorophenol, respectively. Both enzymes discriminated between the two possible directions of 2-chloro-cis, cis-muconate cycloisomerization and converted this substrate to 5-chloromuconolactone as the only product. In contrast to chloromuconate cycloisomerases of gram-negative bacteria, the corresponding R. erythropolis enzyme is unable to catalyze elimination of chloride from (+)-5-chloromuconolactone. Moreover, in being unable to convert (+)-2-chloromuconolactone, the two cycloisomerases of R. erythropolis 1CP differ significantly from the known muconate and chloromuconate cycloisomerases of gram-negative strains. The catalytic properties indicate that efficient cycloisomerization of 3-chloro- and 2,4-dichloro-cis,cis-muconate might have evolved independently among gram-positive and gram-negative bacteria.

4-Butyrolactone↗
PubMed1977

Evolution of bacterial sensitivity to fosfomycin in the Cindad Sanitaria 'Francisco Franco' in Barcelona.

A revision was done of the sensitivity of isolated germs in urine cultures and various other cultures to fosfomycin from 1972 to the present in the Ciudad Sanitaria 'Francisco Franco' in Barcelona. The results obtained were analyzed. The general observation was that of a fairly uniform behavior in the majority of germs that had shown an increase in resistance in 1973, and a clear tendency to a decrease in resistance in 1974 and 1975 with the exception of P. rettgeri (Lact.+) and P. morganii.

Anti-Bacterial Agents↗
PubMed2002

Genome plasticity in Lactococcus lactis.

Comparative genome analyses contribute significantly to our understanding of bacterial evolution and indicate that bacterial genomes are constantly evolving structures. The gene content and organisation of chromosomes of lactic acid bacteria probably result from a strong evolutionary pressure toward optimal growth of these microorganisms in milk. The genome plasticity of Lactococcus lactis was evaluated at inter- and intrasubspecies levels by different experimental approaches. Comparative genomics showed that the lactococcal genomes are not highly plastic although large rearrangements (a.o. deletions, inversions) can occur. Experimental genome shuffling using a new genetic strategy based on the Cre-loxP recombination system revealed that two domains are under strong constraints acting to maintain the original chromosome organisation: a large region around the replication origin, and a smaller one around the putative terminus of replication. Future knowledge of the rules leading to an optimal genome organisation could facilitate the definition of new strategies for industrial strain improvement.

Gene Rearrangement↗
PubMedDate not supplied

[Etiology and evolution of bacterial meningitis in a pediatric center]

OBJECTIVE: To establish the prevalence of the etiological agents of bacterial meningitis in a reference center for the treatment of infectious diseases in the state of Minas Gerais. METHODS: Descriptive study including all children with probable diagnosis of meningitis between June/1999 and November/1999. RESULTS: There were 210 cases of meningitis, and 111 (52.9%) were caused by bacteria. Actually, 52 were probable bacterial meningitis (with liquor alterations) and 59 were confirmed (with culture and/or antigen tests). The main agents were: Haemophilus influenzae, Neisseria meningitidis and Streptococcus pneumoniae. The initial treatment for children aged between three months and five years consisted of ampicillin and chloramphenicol. Later, the antibiotic was changed to penicillin in cases of Neisseria meningitidis and Streptococcus pneumoniae. and to chloramphenicol in cases of Haemophilus influenzae. Extended spectrum antimicrobial agents were used on clinical or laboratory basis, but resistant microorganisms were not found in cultures. CONCLUSIONS: The epidemiology of meningitis should be continuous and should consider local data in order to guide antimicrobial therapy. The continuous monitoring of the prevalent agents in each institution and their resistance is fundamental to the selection of antimicrobial drugs, preserving the antimicrobial agents, and causing less interference with individual colonization, without contributing to the increasing resistance of the agents responsible for meningeal infections.

Journal Article↗
PubMedDate not supplied

[Beta-lactamases in laboratory and their role in resistance Part I.: Evolution of bacterial resistance mediated by beta-lactamases].

Beta-lactamases are the commonest cause of bacterial resistance to beta-lactam antibiotics. They have been classified phenotypically by their isoelectric point, substrate profile, susceptibility to inhibitors and genetic origin. Chromosomal beta-lactamases are typical for certain bacterial species and plasmid beta-lactamases are transferable between different species and genera. Sequencing of beta-lactamase genes enabled to divide them into four classes: A, B, C and D. The ability of a beta-lactamase to confer resistance depends on its location, kinetics, quantity and physicochemical conditions. First beta-lactamases were described soon after introduction of penicillin. Plasmid-mediated broad-spectrum beta-laktamases appeared in the middle 60-s of the XX century and confer resistance to penicillins and some first generation cephalosporins. They include TEM-1, TEM-2, SHV-1, ROB, BRO, OXA and PSE beta-lactamases and are transferred by conjugation between different species and strains of Gram-negative bacteria. The new beta-lactam agents nowadays are compromised mostly by extended-spectrum beta-lactamases, inhibitor-resistant beta-lactamases and carbapenemases. Extended-spectrum beta-lactamases (ESBLs) were described for the first time 20 years ago and are derived from the parental TEM and SHV-1 beta-lactamases by mutations that alter the configuration of the active site to expand their spectrum of activity. They hydrolyse oxymino-cephalosporins and aztreonam. The rapid and accurate laboratory detection of ESBLs is important for choosing appropriate antibiotic therapy. Infections caused by Enterobacteriaceae producing ESBLs pose a therapeutic problem due to multiple antibiotic resistance which includes non-beta-lactam antibiotics as well. Carbapenems are the first-line antibiotics for treatment of such infections.

Bacteria↗
PubMed1991

IFN-gamma inhibits inflammatory cell recruitment and the evolution of bacterial cell wall-induced arthritis.

Localization of streptococcal cell wall Ag (SCW) in the synovial tissue of treated rats induces an influx of leukocytes and a cell-mediated immune response leading to arthritis and joint destruction. Systemic administration of the T cell product, IFN-gamma (10(6) U/kg/day), suppresses the recruitment of leukocytes into the synovium and effectively inhibits the inflammation and pathology characteristic of SCW-induced arthritis (articular index 10.4 +/- 0.6 for SCW vs 2.0 +/- 0.7 for SCW with IFN-gamma, p less than 0.005). Monocyte-macrophages from animals treated with IFN-gamma exhibited defective chemotactic responses when tested in vitro and furthermore, monocytes cultured with IFN-gamma (25 to 500 U/ml) in vitro had significantly suppressed chemotactic responses to the complement fragment C5a (p less than 0.005). The decreased ability to migrate to C5a was associated with decreased binding of fluorochrome-conjugated C5a indicative of reduced expression of C5a receptors. Based on these data, IFN-gamma that induces monocyte maturation as reflected by increased Ia expression conversely inhibits C5a receptor expression. Although locally elevated IFN-gamma levels may serve to inhibit recruitment away from an inflammatory site, systemic exposure to IFN-gamma appears to inhibit leukocyte recruitment to the inflammatory site by its ability to induce premature maturation and concomitant inability to respond to certain chemotactic ligands. Inasmuch as monocyte recruitment to the synovium is pivotal in the development of SCW-induced polyarthritis, the ability of IFN-gamma to inhibit this event effectively inhibits the synovial pathology.

Animals↗
PubMed1989

[Appearance and evolution of bacterial resistance to antibiotics].

Concomitant with antibiotic use has been the appearance of resistance bacteria which seem able to emerge as rapidly as new antibiotics are introduced. Although initially encountered in hospitals, resistant bacteria are now being detected as causes of human and animal infections and as colonizers of the gut. Moreover, resistant bacteria are isolated from the environment.

Animals↗
PubMed2003

High deleterious genomic mutation rate in stationary phase of Escherichia coli.

In natural habitats, bacteria spend most of their time in some form of growth arrest. Little is known about deleterious mutations in such stages, and consequently there is limited understanding of what evolutionary events occur. In a deleterious mutation accumulation experiment in prolonged stationary phase of Escherichia coli, about 0.03 slightly deleterious mutations were observed per genome per day. This is over an order of magnitude higher than extrapolations from fast-growing cells, but in line with inferences from observations in adaptive stationary phase mutation experiments. These findings may affect understanding of bacterial evolution and the emergence of bacterial pathogenicity.

Biological Evolution↗
PubMed2003

Pathogenicity mechanisms of prokaryotic cells: an evolutionary view.

The success of pathogenic microbes depends on their ability to colonize host tissues and to counter host defense mechanisms. Microorganisms can produce overwhelming infection because of their relatively short generation times, and because they have evolved powerful mechanisms for generating phenotypic diversity as an efficient strategy for adapting to rapidly responding immune system defenses and the broad range of polymorphisms characteristic of different host tissues. Bacterial evolution may not be a continuous process, but more of a succession of temporally spaced major events. These events cause a non-gradual sequence of adaptations to a given environment. The pathogenicity islands are genetically unstable elements, and many of the genes coding for the adhesins, toxins and other virulence factors are present in pathogenicity islands, which almost certainly had former lives as accessory elements or as parts thereof, or were borne on functional accessory elements. Novel genes are also acquired by transduction (mediated by bacteriophages, plasmids or transposons), by conjugation (DNA transfer between cells) or by transformation (natural DNA uptake). Horizontal gene transfer from other species is a major source of variation and is fundamental to the genetic theory of adaptive evolution in prokaryotes.

Bacteria↗
PubMed1999

Bacterial population genetics, evolution and epidemiology.

Asexual bacterial populations inevitably consist of an assemblage of distinct clonal lineages. However, bacterial populations are not entirely asexual since recombinational exchanges occur, mobilizing small genome segments among lineages and species. The relative contribution of recombination, as opposed to de novo mutation, in the generation of new bacterial genotypes varies among bacterial populations and, as this contribution increases, the clonality of a given population decreases. In consequence, a spectrum of possible population structures exists, with few bacterial species occupying the extremes of highly clonal and completely non-clonal, most containing both clonal and non-clonal elements. The analysis of collections of bacterial isolates, which accurately represent the natural population, by nucleotide sequence determination of multiple housekeeping loci provides data that can be used both to investigate the population structure of bacterial pathogens and for the molecular characterization of bacterial isolates. Understanding the population structure of a given pathogen is important since it impacts on the questions that can be addressed by, and the methods and samples required for, effective molecular epidemiological studies.

Bacteria↗
PubMed2024

Evolution of homologous recombination rates across bacteria.

Bacteria are nonsexual organisms but are capable of exchanging DNA at diverse degrees through homologous recombination. Intriguingly, the rates of recombination vary immensely across lineages where some species have been described as purely clonal and others as "quasi-sexual." However, estimating recombination rates has proven a difficult endeavor and estimates often vary substantially across studies. It is unclear whether these variations reflect natural variations across populations or are due to differences in methodologies. Consequently, the impact of recombination on bacterial evolution has not been extensively evaluated and the evolution of recombination rate-as a trait-remains to be accurately described. Here, we developed an approach based on Approximate Bayesian Computation that integrates multiple signals of recombination to estimate recombination rates. We inferred the rate of recombination of 162 bacterial species and one archaeon and tested the robustness of our approach. Our results confirm that recombination rates vary drastically across bacteria; however, we found that recombination rate-as a trait-is conserved in several lineages but evolves rapidly in others. Although some traits are thought to be associated with recombination rate (e.g., GC-content), we found no clear association between genomic or phenotypic traits and recombination rate. Overall, our results provide an overview of recombination rate, its evolution, and its impact on bacterial evolution.

Bacteria↗