USE OF SUPPRESSOR ANALYSIS TO FIND GENES INVOLVED IN THE COLONIZATIONDEFICIENCY OF A BACTEROIDES-THETAIOTAOMICRON MUTANT UNABLE TO GROW ONTHE HOST-DERIVED MUCOPOLYSACCHARIDES CHONDROITIN SULFATE AND HEPARIN

Bacteroides thetaiotaomicron, one of the numerically predominant speci es of human colonic bacteria, can ferment two types of host-derived mu copolysaccharides, chondroitin sulfate (CS) and heparin (HP). Original ly, the pathways for utilization of CS and HP appeared to be completel y independent of each other, but we have recently identified a gene, c huR, that links the two utilization systems. chuR is probably a regula tory gene, but it controls only a small subset of genes involved in CS and HP utilization. Some of the genes controlled by chuR are importan t for survival of B. thetaiotaomicron in the colon because a mutant th at no longer produced ChuR was unable to compete with the wild type fo r colonization of the intestinal tract of germfree mice. In an attempt to identify genes that either were controlled by ChuR or encoded prot eins that interacted with ChuR, we used transposon mutagenesis to gene rate suppressor mutations that restored the ability of a chuR disrupti on mutant to grow on CS and HP. Two classes of suppressors were isolat ed. One class grew as well as the wild type on CS and HP and had recov ered the ability to compete with the wild type for colonization of the germfree mouse intestinal tract. A second class grew more slowly on C S and HP and reached only a half-maximum level on CS. This mutant stil l had a colonization defect. Representatives of both classes of suppre ssor mutants have been characterized, and the results of this analysis suggest that the transposon insertions in the suppressor mutants prob ably affected regulatory genes whose products interact with ChuR.