Studies on the regulation of biodegradative arginine and lysine decarboxylase gene expression in Escherichia coli
Doctor of Philosophy
The biodegradative arginine decarboxylase and lysine decarboxylases, encoded by adi and cadA, respectively, are induced to maximal levels when E. coli is grown anaerobically in rich medium at acidic pH. They were used as model systems to study how E. coli responds to a specific environmental stress, moderately acidic pH. Two Mu dlac fusion strains, GNB7145K (adi::lac) and GNB8385K (cadA::lac), were used as genetic tools in our search for transregulating factors involved in acid-induction of these two gene systems. By characterization of random transposon mutagenesis-generated mutants that showed altered expression patterns in response to medium pH, and by studying a series of plasmids that could complement the mutant phenotypes, we identified six genes whose products might be involved in the acid-induction processes. Four of them are likely to be responsible for the basal level of expression at noninducing conditions, three of which, hns, hnsB, and hfq, code for known or putative bacterial histone-like proteins, and one of which, leuO, codes for a putative transcription regulator. The other two, rpoA encoding the $\alpha$ subunit of RNA polymerase, and cysB encoding the positive regulator for cysteine biosynthesis operons, are likely to be involved in the adi activation process at inducing conditions. These findings have allowed us to speculate upon the mechanisms of acid-regulation, particularly of the adi gene system where the regulation seems complex and little previous information was available.