Activity of Bdellovibrio Hit Locus Proteins, Bd0108 and Bd0109, Links Type IVa Pilus Extrusion/Retraction Status to Prey-Independent Growth Signalling

摘要

Bdellovibrio bacteriovorus are facultatively predatory bacteria that grow within gram-negative prey, using pili toudinvade their periplasmic niche. They also grow prey-independently on organic nutrients after undergoing a reversibleudswitch. The nature of the growth switching mechanism has been elusive, but several independent reports suggestedudmutations in the hit (host-interaction) locus on the Bdellovibrio genome were associated with the transition to preyindependentudgrowth. Pili are essential for prey entry by Bdellovibrio and sequence analysis of the hit locus predictedudthat it was part of a cluster of Type IVb pilus-associated genes, containing bd0108 and bd0109. In this study we haveuddeleted the whole bd0108 gene, which is unique to Bdellovibrio, and compared its phenotype to strains containingudspontaneous mutations in bd0108 and the common natural 42 bp deletion variant of bd0108. We find that deletion ofudthe whole bd0108 gene greatly reduced the extrusion of pili, whereas the 42 bp deletion caused greater pilusudextrusion than wild-type. The pili isolated from these strains were comprised of the Type IVa pilin protein; PilA.udAttempts to similarly delete gene bd0109, which like bd0108 encodes a periplasmic/secreted protein, were notudsuccessful, suggesting that it is likely to be essential for Bdellovibrio viability in any growth mode. Bd0109 has audsugar binding YD- repeat motif and an N-terminus with a putative pilin-like fold and was found to interact directly withudBd0108. These results lead us to propose that the Bd0109/Bd0108 interaction regulates pilus production inudBdellovibrio (possibly by interaction with the pilus fibre at the cell wall), and that the presence (and possibly retractionudstate) of the pilus feeds back to alter the growth state of the Bdellovibrio cell. We further identify a novel small RNAudencoded by the hit locus, the transcription of which is altered in different bd0108 mutation backgrounds