Abstract
Application of in vivo expression technology (IVET) to Yersinia ruckeri, an important fish pathogen, allowed the identification of two adjacent genes that represent a novel bacterial system involved in the uptake and degradation of l-cysteine. Analysis of the translational products of both genes showed permease domains (open reading frame 1 [ORF1]) and amino acid position identities (ORF2) with the l-cysteine desulfidase from Methanocaldococcus jannaschii, a new type of enzyme involved in the breakdown of l-cysteine. The operon was named cdsAB (cysteine desulfidase) and is found widely in anaerobic and facultative bacteria. cdsAB promoter analysis using lacZY gene fusion showed highest induction in the presence of l-cysteine. Two cdsA and cdsB mutant strains were generated. The limited toxic effect and the low utilization of l-cysteine observed in the cdsA mutant, together with radiolabeled experiments, strongly suggested that CdsA is an l-cysteine permease. Fifty percent lethal dose (LD(50)) and competence index experiments showed that both the cdsA and cdsB loci were involved in the pathogenesis of the bacteria. In conclusion, this study has shown for the first time in bacteria the existence of an l-cysteine uptake system that together with an additional l-cysteine desulfidase-encoding gene constitutes a novel operon involved in bacterial virulence.