Shining light on the alphaproteobacterial general stress response

Abstract

The general stress response (GSR) allows many bacterial species to react to myriad different stressors. In Alphaproteobacteria, this signaling pathway proceeds through the partner-switching PhyR-EcfG sigma-factor mechanism and is involved in multiple life processes, including virulence in Brucella abortus. To date, details of the alphaproteobacterial GSR signaling pathway have been determined using genetic and biochemical work on a diverse set of species distributed throughout the clade. Fiebig and co-workers establish Erythrobacter litoralis DSM 8509 as a genetically tractable lab strain and use it to both directly and indirectly delineate photoresponsive GSR pathways mediated by multiple HWE/ HisKA_2 histidine kinases. The existence of a new phototrophic lab strain allows researchers to compare the GSR across different Alphaproteobacteria, as well as study the interplay between the GSR and phototrophy. Additionally, the discovery of new HWE/HisKA_2 kinases regulating the GSR poses new questions about how different stimuli feed into this widespread stress pathway. Like all organisms, bacteria must respond to a variety of external cues and conditions. One such condition is environmental stress, whether caused by starvation, oxidative stress or any of a number of factors. Many bacteria use a common set of cellular responses, termed the general stress response (GSR), to react to these various conditions encountered throughout their life cycle, including during infection of pathogenic species such as Brucella abortus (Staroń and Mascher, 2010;Kim et al., 2013). In this article of Molecular Microbiology, Fiebig et al., report two key uses of the marine alphaproteobacterium Erythrobacter litoralis DSM 8509 to understand the GSR by both (1) developing this organism as a tractable genetic model and (2) using it to demonstrate how a complex network regulates the GSR in response to light/dark changes, both directly and indirectly (Fiebig et al., 2019). Both sets of findings open up new avenues in bacterial signaling and stress response for researchers to explore.