Diversification of Vibrio anguillarum Driven by the Bacteriophage CHOED

Abstract

Bacteriophages are an important factor in bacterial evolution. Some reports suggest that lytic bacteriophages can select for resistant mutant strains with reduced virulence. The present study explores the role of the CHOED bacteriophage in the diversification and virulence of its host Vibrio anguillarum . Nine phage-resistant strains were analyzed for their phenotype and different virulence factors, showing alterations in their fitness, motility, biofilm formation, lipopolysaccharide profiles and/or protease activity. Seven of the nine phage-resistant strains showed virulence reduction in a Sparus aurata larvae model. However, this is not generalized since two of the resistant strains show equal virulence compared with the parental strain. The genomic analysis of representative resistant strains displayed that the majority of the mutations are specific for each isolate, affecting genes related to lipopolysaccharide biosynthesis, quorum sensing, motility, toxin and membrane transport. The observed mutations were coherent with the phenotypic and virulence differences observed. These results suggest that the CHOED phage acts as a selective pressure on V. anguillarum , allowing proliferation of resistant strains with different genotypes, phenotypes and degrees of virulence, contributing to bacterial diversification.

The Development of Bacteriophage Resistance in Vibrio alginolyticus Depends on a Complex Metabolic Adaptation Strategy

“…This observation suggests a phenotypic impact, especially taking into account the very short duplication time of Vibrio species [ 54 ]. This indication corroborates previous results on Vibrio species [ 55 ], which demonstrated various novel traits (including reduced growth) of resistant bacteria to a lytic bacteriophage.…”

“…In any case, complementation experiments have to be performed in order to elucidate the precise molecular role of these genes in the induced phage resistance mechanism. In our case, we could not detect mutations in the case of the main receptors or their possible promoters ( Supplemental Table S3 ), as was reported previously [ 55 ]. It is possible that for the Vibrio genus, spontaneous mutations in phage receptors are not required for impaired adsorption or/and infection.…”

“…Taken together, the observed mutations point towards a molecular mechanism resulting in the drastic transcriptional alterations observed in the current work and subsequently, to metabolic reprogramming of bacteriophage-resistant strains. To this end, our work is in line with previous work on Vibrio anguillarum resistant mutants, which showed various mutations between resistant mutants for a lytic bacteriophage and that transcriptional regulators and sigma factors can be targets of SNPs, with diverse metabolical and phenotypical effects [55]. Our work corroborates that study in the Vibrio genus.…”

“…The results of the transcript accumulation of membrane proteins hinted towards possible changes in the bacterial intracellular metabolism, a hypothesis tested by studying transcript levels of key metabolic enzymes and by monitoring the intracellular metabolome. Furthermore, possible metabolic reprogramming could account for the observed alterations in bacterial growth [ 55 , 72 , 74 , 75 ] and mobility [ 76 , 77 , 78 ].…”

Characterization of Bacteriophages against Pseudomonas Syringae pv. Actinidiae with Potential Use as Natural Antimicrobials in Kiwifruit Plants

“…In parallel, bacterial cultures inoculated with an equal volume of fresh medium were used as controls. After 48 h of incubation, the frequency of resistance was obtained by calculating the ratio between the concentration of the corresponding Psa strain grown in the presence or absence of the phage [ 40 ]. All assays were performed in biological and technical triplicate.…”