Aim: In Vibrio parahaemolyticus, the clustered regularly interspaced short palindromic repeat (CRISPR)-associated cas6 endoribonuclease gene has been shown to exhibit sequence diversity and has been subtyped into four major types based on its length and composition. In this study, we aimed to detect and characterize the cas6 gene variants prevalent among V. parahaemolyticus strains isolated from seafoods and environment.

Materials and Methods: Novel primers were designed for each of the cas6 subtypes to validate their identification in V. parahaemolyticus by polymerase chain reaction (PCR). In total, 38 V. parahaemolyticus strains isolated from seafoods and environment were screened for the presence of cas6 gene. Few representative PCR products were sequenced, and their phylogenetic relationship was established to available cas6 gene sequences in GenBank database.

Results: Of the 38 V. parahaemolyticus isolates screened, only about 40% of strains harbored the cas6 endoribonuclease gene, among which 31.6% and 7.9% of the isolates were positive for the presence of the cas6-a and cas6-d subtypes of the gene, respectively. The subtypes cas6-b and cas6-c were absent in strains studied. Sequence and phylogenetic analysis also established the cas6 sequences in this study to match GenBank sequences for cas6-a and cas6-d subtypes.

Conclusion: In V. parahaemolyticus, the Cas6 endoribonuclease is an associated protein of the CRISPR-cas system. CRISPR-positive strains exhibited genotypic variation for this gene. Primers designed in this study would aid in identifying the cas6 genotype and understanding the role of these genotypes in the CRISPR-cas immune system of the pathogen.

Keywords: cas6 gene, clustered regularly interspaced short palindromic repeats-cas operon, endoribonuclease, type IF system, Vibrio parahaemolyticus.

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