The B. bacteriovorus HD100 genome encodes several potential sigma factors for RNA polymerase which may contribute to such organised waves of gene regulation . The Bdellovibrio bacteriovorus HD100 genome has several predicted “housekeeping”
sigma factors: gene bd0242 Captisol encoding an RpoD sigma 70 sigma factor; gene bd3318, encoding a FliA-like sigma factor and gene bd0843 encoding an RpoN-like sigma factor. In addition, there are two homologues of genes predicted to encode Group IV-this website RpoE-like sigma factors, bd0881 (product predicted at 162 amino-acids) and bd0743 (product predicted at 206 amino-acids). Further, gene bd3314 is predicted to encode a larger sigma factor homologue (predicted at 373 amino-acids) with sigma 70 homology. RpoE-like sigma factors in other bacteria mediate
gene selleck compound expression in response to changes in host/external environment and bacteria with mutations in rpoEs can be defective in virulence or other host interactions . Bd0881 and Bd0743 predicted proteins show significant homology (28.6% and 31.8% identity respectively) to the rpoE gene product of E. coli which encodes a sigma factor of the ECF type that is responsive to extra-cytoplasmic, periplasmic events; RpoE in E. coli is sequestered at the inner membrane by an RseA RseB pair of proteins, until inducing-events, in the shape of abnormally folded proteins in the periplasm, cause it to be released and active . The Bdellovibrio genome, like that of other delta-proteobacteria, does not contain rseAB genes, suggesting that the RpoE-like sigma factors encoded by bd0881 and bd0743 belong more generally to the Group IV-type sigma factors. Unlike some members of this group, the Bdellovibrio genes lack the typical downstream co-transcribed gene encoding a product with homology to an anti-sigma factor. Indeed the genes (bd0745 and bd0882) that are immediately downstream of bd0743 Tau-protein kinase and bd0881
are unique to the Bdellovibrio genome, with no other significant homologues in other bacteria. We hypothesised that the regulatory functions of alternate Group IV sigma factors might be diverse and important in the Bdellovibrio lifestyle, where prey-interaction versus prey-independent axenic growth brings with it many different challenges to the cell, including outer membrane insults, and a need for a great deal of de novo protein synthesis. Thus we used directed mutagenesis with kanamycin cartridge insertion, to test if inactivation of the three sigma factor genes bd3314, bd0881 and bd0743, affected viability and to determine what their regulatory roles in the Bdellovibrio axenic and predatory lifestyles may be. We find that one is likely essential, one is involved in regulating predatory processes and one is involved in repression of different components of the GroESEL chaperone complex, which themselves may have different roles in the predatory lifecycle.