Closely Related Vibrio alginolyticus Strains Encode an Identical Repertoire of Caudovirales-Like Regions and Filamentous Phages

Abstract

Many filamentous vibriophages encode virulence genes that lead to the emergence of pathogenic bacteria. Most genomes of filamentous vibriophages characterized up until today were isolated from human pathogens. Despite genome-based predictions that environmental Vibrios also contain filamentous phages that contribute to bacterial virulence, empirical evidence is scarce. This study aimed to characterize the bacteriophages of a marine pathogen, Vibrio alginolyticus (Kiel-alginolyticus ecotype) and to determine their role in bacterial virulence. To do so, we sequenced the phage-containing supernatant of eight different V. alginolyticus strains, characterized the phages therein and performed infection experiments on juvenile pipefish to assess their contribution to bacterial virulence. We were able to identify two actively replicating filamentous phages. Unique to this study was that all eight bacteria of the Kiel-alginolyticus ecotype have identical bacteriophages, supporting our previously established theory of a clonal expansion of the Kiel-alginolyticus ecotype. We further found that in one of the two filamentous phages, two phage-morphogenesis proteins (Zot and Ace) share high sequence similarity with putative toxins encoded on the Vibrio cholerae phage CTXΦ. The coverage of this filamentous phage correlated positively with virulence (measured in controlled infection experiments on the eukaryotic host), suggesting that this phage contributes to bacterial virulence.

Higher phage virulence accelerates the evolution of host resistance

“…. Even though we have not yet identified any associated ecological benefits, the high prevalence of VALGΦ8 in natural V. alginolyticus isolates (Chibani, Hertel et al 2020) suggests that this phage may provide a selective advantage outside the laboratory in its natural environment, i.e., the pipefish. Conversely, however, bacterial genomes are graveyards of defective prophages (Bobay, Touchon et al 2014), including filamentous phages (Davis, Moyer et al 2000), suggesting that decay, rather than a peaceful coexistence, may be a common outcome for phages integrated into bacterial genomes.…”

“…K01M1 contains one integrated filamentous Vibrio phage VALGΦ6 (later called: resident K01M1Φ-phage throughout the manuscript), which replicates at a very low frequency (19). Compared to other, closely related V. alginolyticus strains, K01M1 is highly susceptible to infections by filamentous phages (14).…”

“…Since motility is an important fitness factor in the natural environment (18) we predict that the replacement of SIE by non-motile MSHA-mutants is constrained to laboratory environments, where such antagonistic pleiotropic costs of surface receptor modifications are lower than the costs of SIE. Selective pressures occurring in the natural environment, such as resource competition in eukaryotic hosts, might reverse this effect and explain why filamentous phages, including high virulent versions of VALGΦ8 persist in environmental isolates (19).…”

<italic>Inoviruses</italic>—the neglected “lurkers” in prokaryotic viruses

“…目前已经分离的丝状病毒有 62 种(表 1), 它们主要以革兰氏阴性菌为宿主. 其中有 17 种侵染 弧菌属(Vibrio)的细菌 [10,[12][13][14][15][16][17][18][19][20][21][22][23][24][25] , 其他分离较多的丝状 病毒宿主包括劳尔氏菌属(Ralstonia) [26][27][28][29][30][31][32] 、黄单胞菌 属(Xanthomonas) [33][34][35][36][37][38][39] 的菌株(图 1A).…”

Pipefish Locally Adapted to Low Salinity in the Baltic Sea Retain Phenotypic Plasticity to Cope With Ancestral Salinity Levels

“…The strain was evolved for 90 days either at 15 or 7 PSU [medium 101: 0.5% (w/v) peptone, 0.3% (w/v) meat extract, 1.5% (w/v) or 0.7% (w/v) NaCl in Milli-Q deionized water] (Goehlich, Roth et al, unpublished data). We used the same strain and evolved it at two different salinities to ensure that salinity is the only driver for potential differences in bacterial virulence, which could also be influenced by the presence of filamentous phages (Waldor and Mekalanos, 1996;Ilyina, 2015;Chibani et al, 2020a).…”