Evidence for Differential Regulation of Genes in the Chondroitin Sulfate Utilization Pathway of Bacteroides thetaiotaomicron

Expression of the chondroitin sulfate utilization (csu) genes of Bacteroides thetaiotaomicron is regulated by chondroitin sulfate. We have now found, however, that the csu genes are not all regulated in the same way. In particular, the gene encoding,-glucuronidase (csuE) is expressed under two different conditions that do not lead to expression of other csu genes. Bacteroides thetaiotaomicron, an obligate anaerobe found in high concentrations in the human colon, is notable for its ability to ferment a variety of polysaccharides (9). One of these polysaccharides is chondroitin sulfate (CS), a linear mucopolysaccharide consisting of repeating units of gluc-uronic acid linked to 4- or 6-sulfated N-acetylgalactosamine. The structures of the two isomers of CS and the enzymes involved in CS breakdown are shown in Fig. 1. Results of previous studies had shown that elevated levels of the enzymes shown in Fig. 1 were seen only when B. thetaio-taomicron was grown in medium containing one of th