Complete genome sequencing and characterization of single-stranded DNA Vibrio parahaemolyticus phage from inland saline aquaculture environment.

Despite their evolutionary, molecular biology and biotechnological significance, relatively fewer numbers of single-stranded DNA (ssDNA) filamentous phages belonging to the family Inoviridae have been discovered and characterized to date. The present study focused on genome sequencing and characterization of an ssDNA Vibrio parahaemolyticus phage V5 previously isolated from an inland saline shrimp culture farm. The complete circular genome of phage V5 consisted of 6658 bp with GC content of 43.7%. During BLASTn analysis, only 36% of phage V5 genome matched with other Vibrio phage genomes in the NCBI database with a sequence identity value of 79%. During the phylogenetic analysis, phage V5 formed a separate branch in the minor clade. These features indicate the novel nature of the phage V5 genome. Among 10 predicted open reading frames (ORFs) in the phage V5 genome, 6 encoded for the proteins of known biological functions, whereas the rest were classified as hypotheticals. Proteins involved in replication and structural assembly were encoded by the phage genome. However, the absence of genes encoding for DNA/RNA polymerases and tRNAs signified that phage V5 is dependent on the host`s molecular machinery for its propagation. As per our knowledge, this is the first study describing the novel genome sequence of an ssDNA V. parahaemolyticus phage from the inland saline environment.

Isolation and Characterization of Bacteriophages from Inland Saline Aquaculture Environments to Control Vibrio parahaemolyticus Contamination in Shrimp.

Among the various bacterial pathogens associated with the aquaculture environment, Vibrio parahaemolyticus the important one from shrimp and human health aspects. Though having been around for several decades, phage-based control of bacterial pathogens (phage therapy) has recently re-emerged as an attractive alternative due to the availability of modern phage characterization tools and the global emergence of antibiotic-resistant bacteria. In the present study, a total of 12 V. parahaemolyticus specific phages were isolated from 264 water samples collected from inland saline shrimp culture farms. During the host range analysis against standard/field isolates of V. parahaemolyticus and other bacterial species, lytic activity was observed against 2.3-45.5% of tested V. parahaemolyticus isolates. No lytic activity was observed against other bacterial species. For genomic characterization, high-quality phage nucleic acid with concentrations ranging from 7.66 to 220 ng/µl was isolated from 9 phages. After digestion treatments with DNase, RNase and S1 nuclease, the nature of phage nucleic acid was determined as ssDNA and dsDNA for 7 and 2 phages respectively. During transmission electron microscopy analysis of phage V5, it was found to have a filamentous shape making it a member of the family Inoviridae. During efficacy study of phage against V. parahaemolyticus in shrimp, 78.1% reduction in bacterial counts was observed within 1 h of phage application. These results indicate the potential of phage therapy for the control of V. parahaemoyticus in shrimp. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s12088-021-00934-6.