SUMMARY: Four spp. capable of utilizing bile acids as sole carbon source were examined for the presence of plasmids. One plasmid was found in sp. RAL8, but no plasmids could be detected in the other three strains. Mitomycin C curing of RAL8 did not affect the ability of the strain to grow on bile acids. This suggested that the genetic information for bile acid catabolism in all four strains was chromosomally located. To isolate bile acid catabolic genes, DNA from RAL8 was partially digested with 3A, then the DNA fragments cloned into the broad-host-range cosmid vector pMMB33. The resulting gene bank was screened by plate-mating with two stable RAL8 mutants. Four of the gene bank clones were found to give a positive complementation with one or both mutants. Examination of the plasmids in the four clones revealed that they were unstable, but detailed mapping enabled a 52 kb restriction map to be derived. Further complementation work showed that two of the bile acid catabolic genes are located close together on the map, and may be contiguous.


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