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J. Bacteriol. doi:10.1128/JB.00671-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Virulence and prodigiosin antibiotic biosynthesis in Serratia are regulated pleiotropically by the GGDEF/EAL domain protein, PigX

Department of Biochemistry, University of Cambridge, Cambridge, CB2 1QW, UK

^* To whom correspondence should be addressed. Email: gpcs{at}mole.bio.cam.ac.uk.

	Abstract

Gram-negative bacteria of the genus Serratia are opportunistic human, plant and insect pathogens. Serratia sp. ATCC 39006 secretes pectinases and cellulases and produces the carbapenem and prodigiosin secondary metabolites. Mutation of a gene (pigX) resulted in an extremely pleiotropic phenotype: prodigiosin antibiotic biosynthesis, plant virulence and pectinase production were all elevated. PigX controlled secondary metabolism by repressing transcription of the target prodigiosin biosynthetic operon (pigA-O). The transcriptional start site of pigX was determined and pigX expression occurred in parallel with Pig production. Detailed quantitative intracellular proteome analyses enabled the identification of numerous downstream targets of PigX, including OpgG, mutation of which reduced production of the plant cell wall degrading enzymes and virulence. The highly pleiotropic PigX regulator contains GGDEF and EAL domains with non-canonical motifs and is predicted to be membrane associated. Genetic evidence suggests that PigX might function as a c-di-GMP phosphodiesterase. This is the first characterization of a GGDEF and EAL domain protein in Serratia and the first example of regulation of antibiotic production by a GGDEF/EAL domain protein.