Steroid degradation genes in Comamonas testosteroni TA441: Isolation of genes encoding a Δ4(5)-isomerase and 3α- and 3β-dehydrogenases and evidence for a 100 kb steroid degradation gene hot spot.

In previous studies, we identified two major Comamonas testosteroni TA441 gene clusters involved in steroid degradation. Because most of the genes included in these clusters were revealed to be involved in degradation of basic steroidal structures and a few were suggested to be involved in the degradation of modified steroid compounds, we investigated the spectrum of steroid compounds degradable for TA441 to better identify the genes involved in steroid degradation. TA441 degraded testosterone, progesterone, epiandrosterone, dehydroepiandrosterone, cholic acid, deoxycholic acid, chenodeoxycholic acid, and lithocholic acid. The results suggested TA441 having 3α-dehydrogenase and Δ4(5)-isomerase, and 3β-,17β-dehydrogenase gene, we isolated these genes, all of which had high homology to the corresponding genes of C. testosteroni ATCC11996. Results of gene-disruption experiments indicated that 3β,17β-dehydrogenase is a unique 3β-dehydrogenase which also acts as a 17β-dehydrogenase in TA441, and there will be at least one more enzyme with 17β-dehydrogenating activity. The 3α-dehydrogenase and Δ4(5)-isomerase genes were found adjacent in the DNA region between the two main steroid degradation gene clusters together with a number of other genes that may be involved in steroid degradation, suggesting the presence of a steroid degradation gene hot spot over 100 kb in size in TA441.