Stress Responses in Bacteria Induced by a Giant Channel

Pathogenic bacteria export large proteins and protein complexes, including virulence factors, using dedicated trans-envelope multi-protein machineries, collectively called secretion systems. Four of these protein export machines found in Gram-negative bacteria: type 2 and 3 secretion systems, the type 4 pilus biogenesis system and the filamentous phage assembly-secretion system (FFSS), contain large homologous gated channels in the outer membrane, called secretins. These channels are radially symmetrical homomultimers (luminal diameter 6-8 nm) interrupted by an internal septum, which blocks the channel in its resting state. By analyzing the transcriptome of Escherichia coli producing the FFSS secretin pIV and an isogenic leaky-gate variant, we have expanded the known secretin responses to include the Sox, Cpx, Rcs and RyhB regulons, in addition to the known secretin responder, the Psp regulon. Furthermore, we show that responses dependent on transcriptional regulators CpxR, SoxS and RcsB (in addition to PspF) are required for survival of E. coli producing the leaky-gate variant of secretin pIV, while CpxR, SoxS and PspF are required for survival of cells producing wild-type T3SS secretin InvG. Our analysis shows that secretins induce three out of six envelope stress responses and responses to oxidative stress. Identification of the key stress response regulators required for survival of secretin stress suggests pathways that may be of interest in developing strategies for control of secretin-expressing pathogenic bacteria. Overall design: mRNA profiles for E. coli cultures expressing either vector control, wildtype pIV or pIV-E292K were deep sequenced in triplicate on 2 lanes of the Illumina HiSeq 2000 platform