Achterholt S

Capyk JK

Dresen C

Grimm MB

Hayakawa S

Horinouchi M

Hu Y

Kendall SL

McLeod MM

Mohn WW

Pandey AK

Rosloniec KZ

Tenneson ME

van der Geize R

Wilkinson CJ

ABSTRACT
          
            Bile acids are highly abundant steroids with important functions in vertebrate digestion. Their catabolism by bacteria is an important component of the carbon cycle, contributes to gut ecology, and has potential commercial applications. We found that
            Rhodococcus jostii
            RHA1 grows well on cholate, as well as on its conjugates, taurocholate and glycocholate. The transcriptome of RHA1 growing on cholate revealed 39 genes upregulated on cholate, occurring in a single gene cluster. Reverse transcriptase quantitative PCR confirmed that selected genes in the cluster were upregulated 10-fold on cholate versus on cholesterol. One of these genes,
            kshA3
            , encoding a putative 3-ketosteroid-9α-hydroxylase, was deleted and found essential for growth on cholate. Two coenzyme A (CoA) synthetases encoded in the cluster, CasG and CasI, were heterologously expressed. CasG was shown to transform cholate to cholyl-CoA, thus initiating side chain degradation. CasI was shown to form CoA derivatives of steroids with isopropanoyl side chains, likely occurring as degradation intermediates. Orthologous gene clusters were identified in all available
            Rhodococcus
            genomes, as well as that of
            Thermomonospora curvata
            . Moreover,
            Rhodococcus equi
            103S,
            Rhodococcus ruber
            Chol-4 and
            Rhodococcus erythropolis
            SQ1 each grew on cholate. In contrast, several mycolic acid bacteria lacking the gene cluster were unable to grow on cholate. Our results demonstrate that the above-mentioned gene cluster encodes cholate catabolism and is distinct from a more widely occurring gene cluster encoding cholesterol catabolism.
          </jats:p

Gene Cluster Encoding Cholate Catabolism in Rhodococcus spp

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