Novel mechanisms of type IV pilus regulation in Acinetobacter baylyi

Bacteria employ extracellular appendages called type IV pili (T4P) to interact with their environment. T4P are essential for diverse microbial behaviors including DNA uptake, surface sensing, virulence, protein secretion, and twitching motility (1). While T4P have been studied extensively, our understanding of these nanomachines largely comes from work on a few model species. Here, we develop Acinetobacter baylyi as a new model organism to study T4P and uncover several unreported mechanisms of T4P regulation. First, using recently-developed T4P-labeling methods (2, 3), we demonstrate that A. baylyi T4P are synthesized on one side of the cell body along the long axis of the cell, and we uncover that this pattern is dependent on components of a conserved chemosensory pathway. Second, we overturn the current dogma that T4P extension occurs through the action of a single, highly conserved ATP-hydrolyzing motor (ATPase) called PilB by showing that T4P synthesis in A. baylyi is dependent on two partially redundant and phylogenetically distinct motors, PilB and PilB2. Third, we uncover a small protein inhibitor of T4P synthesis that specifically inhibits PilB but not PilB2 activity. Together, these results demonstrate novel mechanisms of T4P regulation, which have broad implications for the unexplored diversity of T4P biology in microbial species.