Bdellovibrio bacteriovorus are facultatively predatory bacteria that grow within gram-negative prey, using pili to
invade their periplasmic niche. They also grow prey-independently on organic nutrients after undergoing a reversible
switch. The nature of the growth switching mechanism has been elusive, but several independent reports suggested
mutations in the hit (host-interaction) locus on the Bdellovibrio genome were associated with the transition to preyindependent
growth. Pili are essential for prey entry by Bdellovibrio and sequence analysis of the hit locus predicted
that it was part of a cluster of Type IVb pilus-associated genes, containing bd0108 and bd0109. In this study we have
deleted the whole bd0108 gene, which is unique to Bdellovibrio, and compared its phenotype to strains containing
spontaneous mutations in bd0108 and the common natural 42 bp deletion variant of bd0108. We find that deletion of
the whole bd0108 gene greatly reduced the extrusion of pili, whereas the 42 bp deletion caused greater pilus
extrusion than wild-type. The pili isolated from these strains were comprised of the Type IVa pilin protein; PilA.
Attempts to similarly delete gene bd0109, which like bd0108 encodes a periplasmic/secreted protein, were not
successful, suggesting that it is likely to be essential for Bdellovibrio viability in any growth mode. Bd0109 has a
sugar binding YD- repeat motif and an N-terminus with a putative pilin-like fold and was found to interact directly with
Bd0108. These results lead us to propose that the Bd0109/Bd0108 interaction regulates pilus production in
Bdellovibrio (possibly by interaction with the pilus fibre at the cell wall), and that the presence (and possibly retraction
state) of the pilus feeds back to alter the growth state of the Bdellovibrio cell. We further identify a novel small RNA
encoded by the hit locus, the transcription of which is altered in different bd0108 mutation backgrounds
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)