Untersuchungen zu den Regulationsmechanismen der Typ IV-Pilingene aus Azoarcus sp. BH72 und der Involvierung von Quorum Sensing

Azoarcus sp. BH72 is a diazotrophic grass endophyte. The interaction with the rice plant is mediated by the type IV pilus, which is encoded by the pilAB operon. In the genome sequence pilT was identified, which encodes for a putative type IV pilus retraction protein. To gain more insights into the role of type IV pili during the colonization process, the pilT and pilA genes were inactivated by mutagenesis. Both mutants were abolished in twitching motility. Enhanced piliation of the pilT mutant indicates that indeed PilT has a role in pilus retraction. Studies on rice root colonization revealed that the retractile force mediated by PilT is not essential for the bacterial colonization of the plant surface, but that twitching motility is necessary for invasion and establishment inside the plant.Monitoring the pilAB expression with the reporter genes gusA and gfp at various time points revealed an induction of the pilAB gene expression in a cell density dependent manner. Experiments led to the assumption that Azoarcus doesn`t use an AHL based quorum sensing system, but probably uses a novel autoinducer (HSF, hydrophilic signal factor) for intercellular communication.