Abstract
Filamentous phages have distinguished roles in conferring many pathogenicity and survival related features to Gram-negative bacteria including the medically important Vibrio cholerae, which carries factors such as cholera toxin on phages. A novel filamentous phage, designated VFJΦ, was isolated in this study from an ampicillin and kanamycin-resistant O139 serogroup V. cholerae strain ICDC-4470. The genome of VFJΦ is 8555 nucleotides long, including 12 predicted open reading frames (ORFs), which are organized in a modular structure. VFJΦ was found to be a mosaic of two groups of V. cholerae phages. A large part of the genome is highly similar to that of the fs2 phage, and the remaining 700 bp is homologous to VEJ and VCYΦ. This 700 bp region gave VFJΦ several characteristics that are not found in fs2 and other filamentous phages. In its native host ICDC-4470 and newly-infected strain N16961, VFJΦ was found to exist as a plasmid but did not integrate into the host chromosome. It showed a relatively wide host range but did not infect the classical biotype O1 V. cholerae strains. After infection, the host strains exhibited obvious inhibition of both growth and flagellum formation and had acquired a low level of ampicillin resistance and a high level of kanamycin resistance. The antibiotic resistances were not directly conferred to the hosts by phage-encoded genes and were not related to penicillinase. The discovery of VFJΦ updates our understanding of filamentous phages as well as the evolution and classification of V. cholerae filamentous phage, and the study provides new information on the interaction between phages and their host bacteria.
Highlights
Inovirus, which members are commonly called filamentous bacteriophages, is a special phage genus
Filamentous bacteriophages are widespread among Gram-negative bacteria and have two major types of life cycles, exclusive episomal replication and chromosomal integration combined with episomal replication, the latter of which has been observed for temperate phages [1]
The most wellstudied V. cholerae phage, CTXW, exists as a prophage in toxigenic V. cholerae and encodes the cholera toxin (CT); it plays a crucial role in the pathogenicity of V. cholerae and its transfer between cells [9,10,11,12,13]
Summary
Inovirus, which members are commonly called filamentous bacteriophages, is a special phage genus. Filamentous bacteriophages are widespread among Gram-negative bacteria and have two major types of life cycles, exclusive episomal replication and chromosomal integration combined with episomal replication, the latter of which has been observed for temperate phages [1]. Filamentous phages have provided many key phenotypes to their V. cholerae hosts, including virulence attributes. Phage fs can horizontally transfer its rstC gene to the classical strain and influence the assembly of fimbriae in an animal model [14]. Almost all of these phages have been proven to be integrated into the host chromosome [6,9,15,16]
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