Investigating the type VI secretion system in diazotrophic, grass endophyte Azoarcus sp. strain BH72

The predicted T6SS gene clusters found within the genome of Azoarcus sp. BH72 were examined and found to share characteristics of T6SSs described in literature. The presence of Hcp in culture supernatants confirmed T6SS activity. Furthermore, deletion of predicted core components manipulated the on and off secretion status. In a secretome analysis, the secreted effector protein(s) could not be distinguished, but T6SS-2 components were more represented than T6SS-1 components. In plant experiments, rice inoculated with a T6SS deficient strain responded differently than when inoculated with wild type. Additionally, the T6SS deficient strain colonized rice seedlings in higher numbers than wild type. Finally, in a quest to identify T6SS transcriptional regulators, several potential regulators were screened. Azo0559 was determined to at least partially activate expression of T6SS-1.