Synthesis of Extracellular Polysaccharide, Extracellular Enzymes, and Xanthomonadin in Xanthomonas campestris: Evidence for the Involvement of Two Intercellular Regulatory Signals

In previous work, the pigB transcriptional unit of Xanthomonas campestris was implicated in the generation of a diffusible factor (DF) that regulates xanthomonadin and extracellular polysaccharide (EPS) production. Similarly, the rpfF and rpfB genes were implicated in the generation of a diffusible factor (DSF) that regulates the production of extracellular enzymes and EPS. In this study, extracel-lular cross-feeding studies with rpfF and pigB mutant strains provided evidence for the existence of two separate intercellular signaling systems with overlapping roles in the regulation of EPS production.