Direct evidence of recombination in the recA gene of Aeromonas bestiarum

tTwo hundred and twenty-one strains representative of all Aeromonas species were characterized usingthe recA gene sequence, assessing its potential as a molecular marker for the genus Aeromonas. The inter-species distance values obtained demonstrated that recA has a high discriminatory power. Phylogeneticanalysis, based on full-length gene nucleotide sequences, revealed a robust topology with clearly sepa-rated clusters for each species. The maximum likelihood tree showed the Aeromonas bestiarum strains ina well-defined cluster, containing a subset of four strains of different geographical origins in a deep inter-nal branch. Data analysis provided strong evidence of recombination at the end of the recA sequences inthese four strains. Intergenomic recombination corresponding to partial regions of the two adjacent genesrecA and recX (248 bp) was identified between A. bestiarum (major parent) and Aeromonas eucrenophila(minor parent). The low number of recombinant strains detected (1.8%) suggests that horizontal flowbetween recA sequences is relatively uncommon in this genus. Moreover, only a few nucleotide differ-ences were detected among these fragments, indicating that recombination has occurred recently. Finally,we also determined if the recombinant fragment could have influenced the structure and basic functionsof the RecA protein, comparing models reconstructed from the translated amino acid sequences of ourA. bestiarum strains with known Escherichia coli RecA structures

Potential pathogenicity of Aeromonas hydrophila complex strains isolated from clinical, food, and environmental sources

Aeromonas are autochthonous inhabitants of aquatic environments, including chlorinated and polluted waters, although they can also be isolated from a wide variety of environmental and clinical sources. They cause infections in vertebrates and invertebrates and are considered to be an emerging pathogen in humans, producing intestinal and extra-intestinal diseases. Most of the clinical isolates correspond to A. hydrophila, A. caviae, and A. veronii bv. Sobria, which are described as the causative agents of wound infections, septicaemia, and meningitis in immunocompromised people, and diarrhoea and dysenteric infections in the elderly and children. The pathogenic factors associated with Aeromonas are multifactorial and involve structural components, siderophores, quorum-sensing mechanisms, secretion systems, extracellular enzymes, and exotoxins. In this study, we analysed a representative number of clinical and environmental strains belonging to the A. hydrophila species complex to evaluate their potential pathogenicity. We thereby detected their enzymatic activities and antibiotic susceptibility pattern and the presence of virulence genes (aer, alt, ast, and ascV). The notably high prevalence of these virulence factors, even in environmental strains, indicated a potential pathogenic capacity. Additionally, we determined the adhesion capacity and cytopathic effects of this group of strains in Caco-2 cells. Most of the strains exhibited adherence and caused complete lysis

Evolutionary roots and diversification of the genus Aeromonas

Despite the importance of diversification rates in the study of prokaryote evolution, they have not been quantitatively assessed for the majority of microorganism taxa. The investigation of evolutionary patterns in prokaryotes constitutes a challenge due to a very scarce fossil record, limited morphological differentiation and frequently complex taxonomic relationships, which make even species recognition difficult. Although the speciation models and speciation rates in eukaryotes have traditionally been established by analyzing the fossil record data, this is frequently incomplete, and not always available. More recently, several methods based on molecular sequence data have been developed to estimate speciation and extinction rates from phylogenies reconstructed from contemporary taxa. In this work, we determined the divergence time and temporal diversification of the genus Aeromonas by applying these methods widely used with eukaryotic taxa. Our analysis involved 150 Aeromonas strains using the concatenated sequences of two housekeeping genes (approximately 2,000 bp). Dating and diversification model analyses were performed using two different approaches: obtaining the consensus sequence from the concatenated sequences corresponding to all the strains belonging to the same species, or generating the species tree from multiple alignments of each gene. We used BEAST to perform a Bayesian analysis to estimate both the phylogeny and the divergence times. A global molecular clock cannot be assumed for any gene. From the chronograms obtained, we carried out a diversification analysis using several approaches. The results suggest that the genus Aeromonas began to diverge approximately 250 millions of years (Ma) ago. All methods used to determine Aeromonas diversification gave similar results, suggesting that the speciation process in this bacterial genus followed a rate-constant (Yule) diversification model, although there is a small probability that a slight deceleration occurred in recent times. We also determined the constant of diversification (l) values, which in all cases were very similar, about 0.01 species/Ma, a value clearly lower than those described for different eukaryotes

Nous marcadors moleculars per resoldre les espècies del gènere Aeromonas

[cat] En aquesta tesi doctoral s’ha analitzat la utilitat dels gens malat deshidrogenasa (mdh)i recombinasa A (recA) com a marcadors moleculars per a la construcció de filogènies fiables del gènere Aeromonas. Les dades obtingudes han permès l’obtenció, mitjançant mètodes de màxima versemblança (ML) i d’inferència bayesiana (IB), de filogènies amb un alt suport estadístic en la majoria dels nodes dels arbres obtinguts, indicant que els arbres construïts a partir de les seqüències d’aquests gens són robusts. Com a resultat d’aquesta anàlisi, s’han reclassificat algunes soques mal identificades, s’ha detectat un fragment recombinant en 4 soques d’A.bestiarum, del qual s’ha pogut identificar l’inici i final, així com el parental recombinant del que molt probablement deriva aquest segment, i s’ha determinat el possible efecte d’aquest esdeveniment de recombinació a l’estructura i funció de la proteïna RecA. A partir de les filogènies obtingudes i utilitzant un punt de calibratge extern, s’ha determinat l’origen de l’ancestre comú d’Aeromonas i dels diferents llinatges d’aquest gènere bacterià. A més, s’ha pogut establir a partir de diferents aproximacions, el model de diversificació seguit al llarg dels anys en que Aeromonas ha estat evolucionant, així com la seva taxa de diversificació (nombre d’espècies/milió d’anys). Finalment, s’ha comparat l’evolució seguida per Aeromonas, des del seu origen fins a l’actualitat, amb la de totes les espècies animals. Els resultats suggereixen, que des de la gran extinció del Permià-Triàsic, Aeromonas hauria evolucionat paral·lelament a l’augment del nombre dels gèneres animals. L’explosiva proliferació d’organismes multicel·lulars i la seva decisiva influència en l’estructura i funció dels ecosistemes va proporcionar un nou univers de nínxols ecològics potencials pels llinatges bacterians presents. La bona correlació observada entre el nombre de gèneres animals i la diversificació d’Aeromonas en els darrers 250 Ma, podria ser explicada per la colonització d’aquests nous nínxols

The effect of recombination in Aeromonas

Podeu consultar el llibre complet a: http://hdl.handle.net/2445/46988Although several approaches have been attempted, the estimation of recombination frequencies in natural populations of bacteria remains challenging. Previous studies have demonstrated a wide variety of situations among bacterial species, ranging from the clonal diversification of Salmonella or Escherichia coli, which are mainly due to mutation, to the frequent recombination found in Neisseria gonorrhoeae or Helicobacter pylori. Most of the population studies done with bacterial species suggest that recombination occurs in nature but that it is infrequent compared to mutation. Consequently, bacterial populations consist largely of independent clonal lineages. Our research suggests little or null influence of recombination in the genetic structure of "Aeromonas hydrophila Species Complex", despite the presence of some strains with recombinant gene fragments

The effect of recombination in Aeromonas

Podeu consultar el llibre complet a: http://hdl.handle.net/2445/46988Although several approaches have been attempted, the estimation of recombination frequencies in natural populations of bacteria remains challenging. Previous studies have demonstrated a wide variety of situations among bacterial species, ranging from the clonal diversification of Salmonella or Escherichia coli, which are mainly due to mutation, to the frequent recombination found in Neisseria gonorrhoeae or Helicobacter pylori. Most of the population studies done with bacterial species suggest that recombination occurs in nature but that it is infrequent compared to mutation. Consequently, bacterial populations consist largely of independent clonal lineages. Our research suggests little or null influence of recombination in the genetic structure of "Aeromonas hydrophila Species Complex", despite the presence of some strains with recombinant gene fragments

Evolutionary roots and diversification of the genus Aeromonas

Despite the importance of diversification rates in the study of prokaryote evolution, they have not been quantitatively assessed for the majority of microorganism taxa. The investigation of evolutionary patterns in prokaryotes constitutes a challenge due to a very scarce fossil record, limited morphological differentiation and frequently complex taxonomic relationships, which make even species recognition difficult. Although the speciation models and speciation rates in eukaryotes have traditionally been established by analyzing the fossil record data, this is frequently incomplete, and not always available. More recently, several methods based on molecular sequence data have been developed to estimate speciation and extinction rates from phylogenies reconstructed from contemporary taxa. In this work, we determined the divergence time and temporal diversification of the genus Aeromonas by applying these methods widely used with eukaryotic taxa. Our analysis involved 150 Aeromonas strains using the concatenated sequences of two housekeeping genes (approximately 2,000 bp). Dating and diversification model analyses were performed using two different approaches: obtaining the consensus sequence from the concatenated sequences corresponding to all the strains belonging to the same species, or generating the species tree from multiple alignments of each gene. We used BEAST to perform a Bayesian analysis to estimate both the phylogeny and the divergence times. A global molecular clock cannot be assumed for any gene. From the chronograms obtained, we carried out a diversification analysis using several approaches. The results suggest that the genus Aeromonas began to diverge approximately 250 millions of years (Ma) ago. All methods used to determine Aeromonas diversification gave similar results, suggesting that the speciation process in this bacterial genus followed a rate-constant (Yule) diversification model, although there is a small probability that a slight deceleration occurred in recent times. We also determined the constant of diversification (l) values, which in all cases were very similar, about 0.01 species/Ma, a value clearly lower than those described for different eukaryotes

Draft genome sequence of the Aeromonas diversa type strain

We present here the first genome sequence of the Aeromonas diversa type strain (CECT 4254T). This strain was isolated from the leg wound of a patient in New Orleans (Louisiana, USA) and was originally described as Enteric Group 501 and distinguished from A. schubertii by DNADNA hybridization and phenotypical characterization

Draft genome sequence of Aeromonas molluscorum strain 848TT, isolated from bivalve molluscs

We report here the draft genome sequence of Aeromonas molluscorum 848T, the type strain of this Aeromonas species, which was isolated from wedge shells (Donax trunculus) obtained from a retail market in Barcelona, Spain, in 1997