Insights on the regulation and function of the CRISPR/Cas transposition system located in the pathogenicity island VpaI-7 fromVibrio parahaemolyticusRIMD2210633.

CRISPR/Cas mediated transposition is a recently recognized strategy for horizontal gene transfer in a variety of bacterial species. However, our understanding of the factors that control their function in their natural hosts is still limited. In this work we report our initial genetic characterization of the elements associated with the CRISPR/Cas-transposition machinery (CASTm) from Vibrio parahaemolyticus ( Vpa CASTm), which are encoded within the pathogenicity island VpaI-7. Our results revealed that the components of the Vpa CASTm and their associated CRISPR arrays ( Vpa CAST system) are transcriptionally active in their native genetic context. Furthermore, we were able to detect the presence of polycistrons and several internal promoters within the loci that compose the Vpa CAST system. Our results also suggest that the activity of the promoter of the atypical CRISPR array is not repressed by the baseline activity of its known regulator VPA1391 in V. parahaemolyticus . Additionally, we found that the activity of the promoter of tniQ was modulated by a regulatory cascade involving ToxR, LeuO and H-NS. Since it was previously reported that the activity of the Vpa CAST system was less efficient than that of the Vch CAST system at promoting transposition of a miniaturized CRISPR-associated transposon (mini-CAST) in Escherichia coli , we analyzed if the transposition efficiency mediated by the Vpa CAST system could be enhanced inside its natural host V. parahaemolyticus . We provide evidence that this might be the case suggesting that there could be host induction factors in V. parahaemolyticus that could enable more efficient transposition of CASTs.