Biosynthesis of Four Antibiotic Prodiginines in the Marine Bacterium Hahella chejuensis KCTC 2396

Abstract

Hahella chejuensis KCTC 2396, which is a Gram-negative marine bacterium producing an abundant amount of extracellular polysaccharides, produces a red pigment in the cell envelope. The pigment was suspected to be composed of at least four different compounds. The main red-colored fraction was purified and identified as prodigiosin by NMR analysis, and the others were confirmed as norprodigiosin, undecylprodiginine, and dipyrrolyl-dipyrromethene prodigiosin by comparing with the well-known pigments produced by Serratia marcescens Nima and Streptomyces coelicolor A3(2). The production of the four prodiginines having three pyrrolyl rings with different alkyl substituents have not yet been reported in a single microorganism. KCTC 2396 is thought to possess separate pathways for prodiginine production or have key enzymes with reduced substrate-specificity. As prodigiosin is a promising drug showing immunosuppressive and antibiotic effects, the prodigiosin-biosynthetic pathway of KCTC 2396 was analyzed through a structural analysis of intermediates produced by wild-type and mutants. A central bipyrrolyl intermediate, 4-methoxy-2,2',-bipyrrole-5-carboxaldehyde (MBC), was detected by LC-MS/MS. In addition, fosmid clones containing the functional prodigiosin biosynthesis gene cluster were sequenced, and gene organization and function was analyzed by comparing the putative 13 ORFs with the homologous pig and red genes from Serratia spp. and Str. coelicolor A3(2), respectively. These genes were named hap for Hahella prodigiosin. Several putative pathway-specific genes have been selected for functional analysis, which is in progress. Based on the current experimental data and comparisons with other prodigiosine pathways, the prodiginine-biosynthetic pathways in KCTC 2396 are proposed.