Abstract
BackgroundBdellovibrio bacteriovorus HD100 must regulate genes in response to a variety of environmental conditions as it enters, preys upon and leaves other bacteria, or grows axenically without prey. In addition to “housekeeping” sigma factors, its genome encodes several alternate sigma factors, including 2 Group IV-RpoE-like proteins, which may be involved in the complex regulation of its predatory lifestyle.ResultsWe find that one sigma factor gene, bd3314, cannot be deleted from Bdellovibrio in either predatory or prey-independent growth states, and is therefore possibly essential, likely being an alternate sigma 70. Deletion of one of two Group IV-like sigma factor genes, bd0881, affects flagellar gene regulation and results in less efficient predation, although not due to motility changes; deletion of the second, bd0743, showed that it normally represses chaperone gene expression and intriguingly we find an alternative groES gene is expressed at timepoints in the predatory cycle where intensive protein synthesis at Bdellovibrio septation, prior to prey lysis, will be occurring.ConclusionsWe have taken the first step in understanding how alternate sigma factors regulate different processes in the predatory lifecycle of Bdellovibrio and discovered that alternate chaperones regulated by one of them are expressed at different stages of the lifecycle.
Highlights
Bdellovibrio bacteriovorus HD100 must regulate genes in response to a variety of environmental conditions as it enters, preys upon and leaves other bacteria, or grows axenically without prey
Transcriptional studies and bioinformatics show the operon structures for bd0743 and bd0881 Reverse Transcriptase Polymerase Chain Reaction (RT-PCR) on total RNA taken from predatory growth conditions demonstrated that adjacent genes bd0880, bd0881 and bd0882 are co-transcribed in an operon, but that bd0743 was not co-transcribed with the adjacent gene bd0745
We have shown that of three B. bacteriovorus HD100 sigma factor genes with at least partial rpoE homology, one- bd3314, is likely essential for Bdellovibrio cell life and cannot be deleted. bd0881 and bd0743 can be deleted with the Bdellovibrio retaining the ability to grow predatorily or prey-independently
Summary
Bdellovibrio bacteriovorus HD100 must regulate genes in response to a variety of environmental conditions as it enters, preys upon and leaves other bacteria, or grows axenically without prey. Bdellovibrio bacteriovorus HD100 must regulate genes in response to a variety of environmental conditions as it enters, digests, and leaves other Gram-negative bacteria, or when it grows axenically without prey [1,2,3]. 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 [6]. The genes (bd0745 and bd0882) that are immediately downstream of bd0743 and bd0881 are unique to the Bdellovibrio genome, with no other significant homologues in other bacteria
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