Role of the ResDE-Signal Transduction System in Anaerobic Gene Regulation of Bacillus subtilis

Oregon Health & Science University, Portland OR

Investigators

Abstract

Bacteria can change their metabolism when they suddenly encounter an environment devoid of oxygen. This ability allows bacteria to colonize and grow within diverse environments. The genes necessary for bacteria to carry out anaerobic growth are activated in response to oxygen depletion by a mechanism involving a simple signal transduction system. In the soil bacterium, Bacillus subtilis, this system is composed of the proteins ResE and ResD. The sensor kinase ResE, through an as-yet-unknown mechanism, senses oxygen limitation and responds by donating a high-energy phosphate to ResD, a response regulator, which, upon phosphorylation, stimulates the expression of genes required for anaerobic growth, such as the genes encoding an anaerobic gene regulator FNR and nitrite reductase. ResD interacts directly with the promoter region to activate transcription. Unlike the nitrite reductase genes, activation of fnr, while requiring ResD, does not seem to require ResD in its phosphorylated form. The presence of oxygen seems to stimulate removal of phosphate from ResD, a task also carried out by ResE. Mutations in aa3 quinol oxidase genes cause derepression of ResDE-controlled genes under aerobic conditions, indicating that electron flow to oxygen has an inhibitory role on the signal transduction pathway. In addition, aerobic gene activation is heightened by the presence of nitric oxide (NO), which may stimulate the ResD-phosphorylating activity of ResE. The major questions to be answered this project are: (1) How does ResD activate gene expression? (2) What is the significance behind the fact that fnr does not require phosphorylated ResD for its expression? (3) What parts of the ResE protein are important for sensing and transducing signals to ResD in response to stimuli derived from oxygen depletion? (4) How does NO result in ResDE-dependent gene activation? Studies will be carried out to precisely identify the target of ResD in the DNA that constitutes the genes under ResD control. Particular attention will be paid to the architecture and the ResD-binding characteristics of the fnr control region. The domains conserved in the putative sensing domains of ResE will be altered by directed mutagenesis to identify regions necessary for recognizing signals derived from oxygen limitation and NO. This will provide a correlation between specific signals and the functional domains of ResE and will give insight into how cells sense and respond to oxygen depletion.