The PulE ATPase is required for twitching motility and DNA donation during Thermus thermophilus transjugation

Thermus thermophilus can acquire DNA through natural competence and through transjugation, a mechanism that involves a two-step process of DNA secretion (push) and DNA internalization (pull) between mating cells of related species. The natural competence apparatus (NCA) is required in the recipient mate for the pull step. However, how the DNA exits of the donor cell is only partially known. The putative DNA translocase TdtA, encoded in mobile genetic element ICETh1 of T. thermophilus HB27, was shown to be required for DNA donation as reported by (Blesa et al. 2017a). This ring-shaped hexameric ATPase binds to the membrane and likely interacts with yet unknown secretory components that allow the extrusion of DNA through the membrane; thus, a genetic screening to identify additional putative secretory components was performed. Here, we describe that mutants in gene TT_C1844, which encodes a putative AAA-ATPase named PulE, do not synthesize the recently described "narrow" type 4 pili required for twitching motility and made up of the major PilA5 pilin. Concomitantly, pulE mutants also exhibited DNA donation defects during transjugation, suggesting a role of narrow pili in the donation process. However, single pilA5 null mutants still function as DNA donors in transjugation experiments, so we conclude that the need for PulE in transjugation is independent of its role in narrow pili synthesis and twitching motility.