PIGB DETERMINES A DIFFUSIBLE FACTOR NEEDED FOR EXTRACELLULAR POLYSACCHARIDE SLIME AND XANTHOMONADIN PRODUCTION IN XANTHOMONAS-CAMPESTRIS PVCAMPESTRIS

Seven xanthomonadin transcriptional units (pigA through pigG) were ide ntified by transposon saturation mutagenesis within an 18.6-kbp portio n of the previously identified 25.4-kbp pig region from Xanthomonas ca mpestris pv, campestris (strain B-24), Since marker exchange mutant st rains with insertions in one 3.7-kbp portion of pig could not be obtai ned, mutations in this region may be lethal to the bacterium, Compleme ntation analyses with different insertion mutations further defined an d confirmed the seven transcriptional units, Insertional inactivation of one of the transcriptional units, pigB, resulted in greatly reduced levels of both xanthomonadins and extracellular polysaccharide slime, and a pigB-encoding plasmid restored both traits to these strains, pi gB mutant strains could also be restored extracellularly by growth adj acent to strains with insertion mutations in any of the other six xant homonadin transcriptional units, the parent strain (B-24), or strains of five different species of Xanthomonas. Strain B-24 produced a nontr ansforming diffusible factor (DF), which could be restored to pigB mut ants by the pigB-encoding plasmid, Several lines of evidence indicate that DF is a novel bacterial pheromone, different from the known signa l molecules of Vibrio, Agrobacterium, Erwinia, Pseudomonas, and Burkho lderia spp.