Regulation of a Major Metabolic Intersection in Bacillus subtilis
Global regulators that bind key metabolites allow bacteria to rapidly adapt to dynamic environments by coordinating the expression of many genes. In Bacillus subtilis and low G+C Gram-positive bacterial genera including Staphylococcus, Listeria, Streptococcus and Clostridium, CodY controls the expression of dozens of metabolic genes and genes mediating adaptation to nutrient limitation. Some of these bacteria are major human pathogens in which CodY regulates the expression not only of metabolic genes but also some of the most important virulence genes. The branched-chain amino acids isoleucine, leucine and valine (ILV) and GTP activate CodY as a DNA-binding protein biochemically in vitro, but direct evidence for these small molecules acting as physiologically relevant signals for CodY is lacking.
Using genetics, molecular biology and global transcriptional profiling (RNA-Seq) as well as mass spectrometry-based metabolomics, I show that changes in the rate of endogenous ILV synthesis as well as the pools of a guanine nucleotide, presumably GTP, control CodY activity in living cells. Preliminary results indicate that titrating the intracellular pools of CodY signals generates a spectrum of CodY activities that leads to graded gene expression and alterations in central metabolism. Taken together, these data suggest that, during changes in nutrient availability, CodY prioritizes specific pathways most relevant to survival or rapid growth in various environmental niches, including those of the mammalian host. Future research directions involving the re-emerging infectious disease pathogen Staphylococcus aureus will be discussed