An IgaA/UmoB Family Protein from Serratia marcescens Regulates Motility, Capsular Polysaccharide Biosynthesis, and Secondary Metabolite Production

Secondary metabolites are an important source of pharmaceuticals and key modulators of microbe-microbe interactions. The bacteriumSerratia marcescens is part of theEnterobacteriaceae family of eubacteria and produces a number of biologically active secondary metabolites. In this study, we screened for novel regulators of secondary metabolites synthesized by a clinical isolate ofS. marcescens and found mutations in a gene for an uncharacterized UmoB/IgaA family member here namedgumB . Mutation ofgumB conferred a severe loss of the secondary metabolites prodigiosin and serratamolide. ThegumB mutation conferred pleiotropic phenotypes, including altered biofilm formation, highly increased capsular polysaccharide production, and loss of swimming and swarming motility. These phenotypes corresponded to transcriptional changes infimA ,wecA , andflhD . Unlike other UmoB/IgaA family members,gumB was found to be not essential for growth inS. marcescens , yetigaA fromSalmonella enterica ,yrfF fromEscherichia coli , and an uncharacterized predicted ortholog fromKlebsiella pneumoniae complemented thegumB mutant secondary metabolite defects, suggesting highly conserved function. These data support the idea that UmoB/IgaA family proteins are functionally conserved and extend the known regulatory influence of UmoB/IgaA family proteins to the control of competition-associated secondary metabolites and biofilm formation.IMPORTANCE IgaA/UmoB family proteins are found in members of theEnterobacteriaceae family of bacteria, which are of environmental and public health importance. IgaA/UmoB family proteins are thought to be inner membrane proteins that report extracellular stresses to intracellular signaling pathways that respond to environmental challenge. This study introduces a new member of the IgaA/UmoB family and demonstrates a high degree of functional similarity between IgaA/UmoB family proteins. Moreover, this study extends the phenomena controlled by IgaA/UmoB family proteins to include the biosynthesis of antimicrobial secondary metabolites.