Multiplicity of 3-ketosteroid Δ1-dehydrogenase enzymes in Gordonia neofelifaecis NRRL B-59395 with preferences for different steroids

The presence of redundant genes in a genome might enable bacteria to adapt to varying environmental conditions. The genus Gordonia comprises metabolically diverse bacteria that can degrade a wide range of persistent compounds. This paper reports the multiplicity of genes encoding 3-ketosteroid Delta(1)-dehydrogenase (KstD) in Gordonia neofelifaecis NRRL B-59395. KstD is one of the key enzymes in microbial steroid catabolism. Five kstD homologues (kstD1-kstD5) distributed over several phylogenetic groups were investigated in G. neofelifaecis NRRL B-59395. Escherichia coli cells expressing kstD homologues were used to transform different steroids, including cholesterol, cholest-4-en-3-one, 4-androstene-3,17-dione (AD), progesterone, and 16 alpha, 17 alpha-epoxyprogesterone. All five enzymes displayed KstD activity toward 3-ketosteroids, but none were able to transform 3-hydroxysteroid substrates such as cholesterol. KstD2, KstD3, and KstD5 catalyzed the dehydrogenation reaction of 16 alpha, 17 alpha-epoxyprogesterone, while KstD1, KstD3, and KstD4 transformed AD into androsta-1,4-diene-3,17-dione. Transcriptional analyses revealed that the expression of kstD1, kstD3, and kstD4 was upregulated during culture in cholesterol or AD when compared with expression during culture in pyruvic acid. kstD2 and kstD5 were uniquely induced by cholesterol. Thus, the presence of multiple kstD genes in the G. neofelifaecis NRRL B-59395 genome facilitates a dynamic and fine-tuned response to environmental changes.