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At least 1,657 records · Page 92Linked to original sources
PubMed2003

Synergy and contingency as driving forces for the evolution of multiple secondary metabolite production by Streptomyces species.

In this article we briefly review theories about the ecological roles of microbial secondary metabolites and discuss the prevalence of multiple secondary metabolite production by strains of Streptomyces, highlighting results from analysis of the recently sequenced Streptomyces coelicolor and Streptomyces avermitilis genomes. We address this question: Why is multiple secondary metabolite production in Streptomyces species so commonplace? We argue that synergy or contingency in the action of individual metabolites against biological competitors may, in some cases, be a powerful driving force for the evolution of multiple secondary metabolite production. This argument is illustrated with examples of the coproduction of synergistically acting antibiotics and contingently acting siderophores: two well-known classes of secondary metabolite. We focus, in particular, on the coproduction of beta-lactam antibiotics and beta-lactamase inhibitors, the coproduction of type A and type B streptogramins, and the coregulated production and independent uptake of structurally distinct siderophores by species of Streptomyces. Possible mechanisms for the evolution of multiple synergistic and contingent metabolite production in Streptomyces species are discussed. It is concluded that the production by Streptomyces species of two or more secondary metabolites that act synergistically or contingently against biological competitors may be far more common than has previously been recognized, and that synergy and contingency may be common driving forces for the evolution of multiple secondary metabolite production by these sessile saprophytes.

Anti-Bacterial Agents↗
PubMed2005

Potential photosynthesis gene recombination between Prochlorococcus and Synechococcus via viral intermediates.

Genes (psbA and psbD) encoding for photosynthetically important proteins were recently found in a number of cultured cyanophage genomes. This phenomenon may be a beneficial trait to the viruses or their photosynthetic cyanobacterial hosts, or may represent an untapped pool of genes involved in the formation of the photosynthetic apparatus that are prone to lateral gene transfer. Here we show analyses of psbA genes from uncultured environmental viruses and prophage populations. We observe a statistically significant separation between viral genes and their potential Synechococcus hosts' genes, and statistical analyses under models of codon evolution indicate that the psbA genes of viruses are evolving under levels of purifying selection that are virtually indistinguishable from their hosts. Furthermore, our data also indicate the possible exchange and reshuffling of psbA genes between Synechococcus and Prochlorococcus via phage intermediates. Overall, these observations raise the possibility that marine viruses serve as a potential genetic pool in shaping the evolution of cyanobacterial photosynthesis.

Bacterial Proteins↗
PubMed2002

The ycf27 genes from cyanobacteria and eukaryotic algae: distribution and implications for chloroplast evolution.

The two ycf27 genes from the filamentous cyanobacterium Tolypothrix PCC 7601 have been cloned and sequenced. These two genes, previously designated rpaA and rpaB, encode putative transcriptional regulators of the 'OmpR' family. In Synechocystis PCC 6803, homologous genes have been linked to the regulation of transfer of excitation energy from the phycobilisome to photosystem (PS) I and PSII respectively. Partial clones from Spirulina platensis, Dactylococcopsis salina and Synechococcus PCC 7002 have also been sequenced. A table of identity between the proteins confirms that RpaB belongs in the same family as the algal ycf27 proteins. However, RpaA is a rather different protein and should lose the designation ycf27. The loss of rpaB from the plastid genomes of eukaryotic algae is associated with the loss of phycobiliproteins, so it is likely that this gene performs a similar role in algae to that in cyanobacteria. The implications for chloroplast evolution are discussed along with the possible identity of the cognate histidine kinase gene in the plastid genomes.

Bacterial Proteins↗
PubMed2006

Homologous recombination and the pattern of nucleotide substitution in Ehrlichia ruminantium.

Patterns of nucleotide substitution at orthologous loci were examined between three genomes of Ehrlichia ruminantium, the causative agent of heartwater disease of ruminants. The most recent common ancestor of two genomes (Erwe and Erwo) belonging to the Welgevonden strain was estimated to have occurred 26,500-57,000 years ago, while the most recent common ancestor of these two genomes and the Erga genome (Gardel strain) was estimated to have occurred 2.1-4.7 million years ago. The search for genes showing extremely high values of the number of synonymous substitutions per site was used to identify genes involved in past homologous recombination. The most striking case involved the map1 gene, encoding major antigenic protein-1; evidence for homologous recombination is consistent with previous phylogenetic analysis of map1 alleles. At this and certain other loci, homologous recombination may have contributed to the evolution of host-pathogen interactions. In addition, comparison of the patterns of synonymous and nonsynonymous substitution provided evidence for positive selection favoring a high level of amino acid change between the Welgevonden and Gardel strains at a locus of unknown function (designated Erum4340 in the Erwo genome).

Computational Biology↗
PubMed2005

Influence of growth phase on adhesion kinetics of Escherichia coli D21g.

The influence of bacterial growth stage and the evolution of surface macromolecules on cell adhesion have been examined by using a mutant of Escherichia coli K-12. To better understand the adhesion kinetics of bacteria in the mid-exponential and stationary growth phases under flow conditions, deposition experiments were conducted in a well-controlled radial stagnation point flow (RSPF) system. Complementary cell characterization techniques were conducted in combination with the RSPF experiments to evaluate the hydrophobicity, electrophoretic mobility, size, and titratable surface charge of the cells in the two growth phases considered. It was observed that cells in stationary phase were notably more adhesive than those in mid-exponential phase. This behavior is attributed to the high degree of local charge heterogeneity on the outer membranes of stationary-phase cells, which results in decreased electrostatic repulsion between the cells and a quartz surface. The mid-exponential-phase cells, on the other hand, have a more uniform charge distribution on the outer membrane, resulting in greater electrostatic repulsion and, subsequently, less adhesion. Our results suggest that the macromolecules responsible for this phenomenon are outer membrane-bound proteins and lipopolysaccharide-associated functional groups.

Bacterial Adhesion↗
PubMed2003

Evolution of novel cooperative swarming in the bacterium Myxococcus xanthus.

Cooperation among individuals is necessary for evolutionary transitions to higher levels of biological organization. In such transitions, groups of individuals at one level (such as single cells) cooperate to form selective units at a higher level (such as multicellular organisms). Though the evolution of cooperation is difficult to observe directly in higher eukaryotes, microorganisms do offer such an opportunity. Here we report the evolution of novel cooperative behaviour in experimental lineages of the bacterium Myxococcus xanthus. Wild-type strains of M. xanthus exhibit socially dependent swarming across soft surfaces by a mechanism known as 'S-motility' that requires the presence of extracellular type IV pili. In lineages of M. xanthus unable to make pili, a new mechanistic basis for cooperative swarming evolved. Evolved swarming is mediated, at least in part, by enhanced production of an extracellular fibril matrix that binds cells-and their evolutionary interests-together. Though costly to individuals, fibril production greatly enhanced population expansion in groups of interconnected cells. These results show that fundamental transitions to primitive cooperation can readily occur in bacteria.

Antigens, Bacterial↗
PubMed2004

Genomic plasticity of the causative agent of melioidosis, Burkholderia pseudomallei.

Burkholderia pseudomallei is a recognized biothreat agent and the causative agent of melioidosis. This Gram-negative bacterium exists as a soil saprophyte in melioidosis-endemic areas of the world and accounts for 20% of community-acquired septicaemias in northeastern Thailand where half of those affected die. Here we report the complete genome of B. pseudomallei, which is composed of two chromosomes of 4.07 megabase pairs and 3.17 megabase pairs, showing significant functional partitioning of genes between them. The large chromosome encodes many of the core functions associated with central metabolism and cell growth, whereas the small chromosome carries more accessory functions associated with adaptation and survival in different niches. Genomic comparisons with closely and more distantly related bacteria revealed a greater level of gene order conservation and a greater number of orthologous genes on the large chromosome, suggesting that the two replicons have distinct evolutionary origins. A striking feature of the genome was the presence of 16 genomic islands (GIs) that together made up 6.1% of the genome. Further analysis revealed these islands to be variably present in a collection of invasive and soil isolates but entirely absent from the clonally related organism B. mallei. We propose that variable horizontal gene acquisition by B. pseudomallei is an important feature of recent genetic evolution and that this has resulted in a genetically diverse pathogenic species.

Adult↗
PubMedDate not supplied

[Deceleration of vital activity as a universal biochemical mechanism ensuring adaptation of microorganisms to stress factors: a review].

The review deals with a major problem of contemporary biology, i.e., the strategy of persistence of organisms affected by stressors. The primary mechanism of biochemical adaptation of cells is their transition to a specific surviving state, which is characterized by deceleration of vital activity (DVA), a process related to decreased metabolism. According to the latest classification, there are four DVA types: quiescence (endogenous or exogenous), cryptobiosis, anabiosys, and latent life. These states are viewed from a new standpoint, as depending on both the stage of growth and development of the organism and the type of stressor. A brief characterization of cryptobiosis and anabiosys is provided. Quiescence, which is a specific type of DVA, is characterized in greater detail, with emphasis on differences between fungi and bacteria. Endogenous and exogenous quiescence is compared in two types of cells (spores). Changes in the composition of quiescent cells (spores) as compared to their vegetating counterparts involve lipids (membrane-associated and neutral), cytosolic carbohydrates (which serve as a reserve supply of nutritives or act as protectors), water content, RNA/protein synthesis, and cyclic nucleotides (e.g., cAMP). Biochemical mechanisms controlling reversion of DVA (the transition from spores to germinating cells) are also analyzed. In conclusion, consideration is given to the role of DVA in evolution and to the implications of DVA studies for biotechnology, cryogenic preservation, utilization of interstellar space and permafrost territories.

Adaptation, Physiological↗
PubMed2003

Role of mobile DNA in the evolution of vancomycin-resistant Enterococcus faecalis.

The complete genome sequence of Enterococcus faecalis V583, a vancomycin-resistant clinical isolate, revealed that more than a quarter of the genome consists of probable mobile or foreign DNA. One of the predicted mobile elements is a previously unknown vanB vancomycin-resistance conjugative transposon. Three plasmids were identified, including two pheromone-sensing conjugative plasmids, one encoding a previously undescribed pheromone inhibitor. The apparent propensity for the incorporation of mobile elements probably contributed to the rapid acquisition and dissemination of drug resistance in the enterococci.

Adhesins, Bacterial↗
PubMed2000

Evolutionary and molecular analyses of the Borrelia bdr super gene family: delineation of distinct sub-families and demonstration of the genus wide conservation of putative functional domains, structural properties and repeat motifs.

B. turicatae, a causative agent of relapsing fever, carries a polymorphic gene family that is homologous to the bdr gene family of the Lyme disease spirochetes (previously referred to as the rep+ or ORF-E gene family). Here we demonstrate that bdr related genes are widely distributed among pathogenic Borrelia species and exist as large, polymorphic, plasmid carried, gene families. Twenty distinct bdr alleles were identified in isolates of the relapsing fever spirochete, B. hermsii, and were localized to linear plasmids. Cloning and sequence analyses demonstrate that the putative Bdr functional domains (i.e. the phosphorylation motifs and the transmembrane C-terminal domain) are conserved across the genus while other regions of these proteins exhibit variability. An assessment of the evolutionary relationships among all known Bdr protein sequences obtained from five pathogenic Borrelia species revealed that there are distinct Bdr sub-families. The recognition of distinct phyletic clusters serves as the basis of a revised and simplified nomenclature for the bdr proteins that can be applied genus wide. At the biological level the delineation of multiple bdr sub-families within isogeneic populations raises the possibility that there may be functional partitioning among alleles. In summary, the distribution and conservation of the Bdr proteins suggests that they are important in the biology/pathogenesis of the Borrelia at the genus wide level.

Amino Acid Sequence↗
PubMed1995

Streptolydigin-resistant mutants in an evolutionarily conserved region of the beta' subunit of Escherichia coli RNA polymerase.

Mutations conferring streptolydigin resistance onto Escherichia coli RNA polymerase have been found exclusively in the beta subunit (Heisler, L. M., Suzuki, H., Landick, R., and Gross, C. A. (1993) J. Biol. Chem. 268, 25369-25375). We report here the isolation of a streptolydigin-resistant mutation in the E. coli rpoC gene, encoding the beta' subunit. The mutation is the Phe793-->Ser substitution, which occurred in an evolutionarily conserved segment of the beta' subunit. The homologous segment in the eukaryotic RNA polymerase II largest subunit harbors mutations conferring alpha-amanitin resistance. Both streptolydigin and alpha-amanitin are inhibitors of transcription elongation. Thus, the two antibiotics may inhibit transcription in their respective systems by a similar mechanism, despite their very different chemical nature.

Amino Acid Sequence↗
PubMed2003

[Surveillance of Haemophilus influenzae serotypes and antimicrobial resistance in Colombia, 1994-2002].

Invasive disease caused by Haemophilus influenzae serotype b results in high rates of morbidity and mortality among children. In 1994, the Microbiology Group at the Instituto Nacional de Salud (Colombia) initiated a program to detect antimicrobial resistance in H. influenzae. Invasive isolates were collected by hospitals and public health laboratories as part of surveillance programs for acute respiratory infections and acute bacterial meningitis. To determine the evolution of serotypes and antimicrobial resistance patterns, invasive H. influenzae isolates collected from 1994 to 2002 were compared, and the impact of Hib conjugated vaccine in Colombia was reassessed. The analysis included 683 isolates, 379 (55.5%) were recovered from male patients, 370 (54.2%) from children under one year, 227 (33.2%) from children aged 1 to 5, 19 (2.8%) from children aged 6 to 14, and 38 (5.6%) from children over 14 years; 29 (4.2%) with no age data. Clinical classification recorded 493 (72.2%) of the samples were from patients with meningitis, 181 (26.5%) with pneumonia, and 9 (0.9%) with other diseases. Eighty five percent of isolates corresponded to H. influenzae serotype b, 12.9% were non capsular, and 2.0% corresponded to other serotypes (10 a, 1 d, 1 e and 2 f). Of the total number of isolates, 12.0% produced beta lactamase, 13.9% were resistant to ampicillin, 12.7% to trimethoprim sulfamethoxazole (SXT), 5.4% to chloramphenicol, 1% to cefuroxime. All isolates were susceptible to ceftriaxone. During the 10-year period, resistance to SXT increased from 5% to 13%. A significant decrease in meningitis cases was detected among children under one-year old and in the 1 to 5 age group. Before introducing the vaccine, an annual average of 43 and 23 isolates for each of these groups were received. During 2002, 10 and 6 isolates, respectively, were received for each group. Surveillance of invasive H. influenzae isolates has allowed the evaluation of Hib vaccine impact, as well as the detection of an increase of non-capsular isolates, and changes in resistance patterns.

Adolescent↗
PubMed1993

SecA is plastid-encoded in a red alga: implications for the evolution of plastid genomes and the thylakoid protein import apparatus.

Partial sequence analysis of the plastid DNA (ptDNA) from a red alga, Antithamnion sp., revealed the presence of a homologue to the Escherichia coli secA gene as well as two open reading frames (ORF 510, ORF 179). In addition a sec Y homologue has been detected on the plastid genome by heterologous hybridization. None of these genes has been found in completely sequenced chlorophytic plastid genomes. SecA and secY gene copies were also detected in the ptDNA of a chromophytic alga, indicating that secA Y may be ubiquitous in rhodophytes and chromophytes. The significance of these findings for the evolution of plastid genomes and the thylakoid protein import mechanism is discussed.

Adenosine Triphosphatases↗