Elucidation of the Serratia marcescens nucC regulon

Serratia marcescens is an opportunistic pathogen that has been recognized only fairly recently as a significant cause of nosocomial infections. Strains of S. marcescens secrete a number of extracellular degredative enzymes and toxins, including a nuclease, a lipase, chitinases, proteases, and bacteriocins. Expression of the extracellular nuclease and bacteriocin 28b in S. marcescens has been shown to be under the positive control of nucC. The nucC gene encodes a small, zinc-binding protein that belongs to the bacteriophage P2 Ogr family of transcription factors. The nucC gene lies in an operon that appears to be part of a cryptic prophage in the S. marcescens chromosome. The adoption by S. marcescens of a prophage-encoded activator to regulate chromosomal genes has interesting implications for the role of horizontal gene transfer in bacterial evolution. Ogr homologues are found in a number of bacterial genomes, and recently similar proteins have also been identified as positive regulators of levansucrase genes in Rahnella aquatilis and Erwinia amylovora. Preliminary evidence is consistent with the hypothesis that there are a number of genes in S. marcescens under NucC control. Complementary genomic and proteomic approaches are being used to identify these genes and further characterize their regulation.