Regulation of the Erythrobacter litoralis DSM 8509 general stress response by visible light

Abstract

Extracytoplasmic function (ECF) sigma factors are a major class of environmentally-responsive transcriptional regulators. In Alphaproteobacteria the ECF sigma factor, {sigma}EcfG, activates general stress response (GSR) transcription and protects cells from multiple stressors. A phosphorylation-dependent protein partner switching mechanism, involving HWE/HisKA_2-family histidine kinases, underlies {sigma}EcfG activation. The identity of these sensor kinases and the signals that regulate them remain largely uncharacterized. We have developed the aerobic anoxygenic photoheterotrophic (AAP) bacterium, Erythrobacter litoralis DSM 8509, as a comparative genetic model to investigate GSR regulation. Using this system, we sought to define the contribution of visible light and a photosensory HWE kinase, LovK, to GSR transcription. We identified three HWE kinases that collectively regulate GSR: gsrK and lovK are activators, while gsrP is a repressor. GSR transcription is higher in the dark than light, and the opposing activities of gsrK and gsrP are sufficient to achieve light-dependent differential transcription. In the absence of gsrK and gsrP, lovK alone is sufficient to regulate GSR transcription in response to light. This regulation requires a photochemically active LOV domain in LovK. Our studies establish a role for visible light and HWE kinases in light-dependent regulation of GSR transcription in E. litoralis, an AAP species.\n\nGRAPHICAL ABSTRACT\n\nO_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=174 SRC=\"FIGDIR/small/641647v1_ufig1.gif\" ALT=\"Figure 1\">\nView larger version (19K):\norg.highwire.dtl.DTLVardef@65ed9borg.highwire.dtl.DTLVardef@1d25e65org.highwire.dtl.DTLVardef@333ff9org.highwire.dtl.DTLVardef@ad2cf4_HPS_FORMAT_FIGEXP M_FIG C_FIG ABBREVIATED SUMMARYGeneral stress response (GSR) systems protect bacteria from a diverse range of physical and chemical stressors. We have developed Erythrobacter litoralis as a new genetic model to study GSR in Alphaproteobacteria and show that three HWE-family histidine kinases collectively regulate GSR transcription via {sigma}EcfG. Visible light is a GSR regulatory signal in E. litoralis, and LovK is a blue-light photosensor kinase that functions as a dark activated GSR regulator.