A comprehensive approach to explore metabolic and phylogenetic diversity of bacterial steroid degradation
Biodiversity Research Center,
Academia Sinica, Taiwan
Steroid hormones such as androgens are common surface water contaminants. However, current knowledge regarding the ecophysiological relevance of steroid-degrading organisms in the environment, especially anoxic ecosystems, is very limited. Steroidobacter denitrificans can anaerobically degraded androgens via the 2,3-seco pathway. Here, the S. denitrificans genome was completely sequenced. Transcriptomic data revealed the gene clusters distinctly expressed during anaerobic growth on testosterone. We isolated and characterized the bifunctional molybdoenzyme, 1-testosterone hydratase/dehydrogenase, which is essential for steroidal core-ring degradation. Because of its high substrate specificity, the corresponding genes, along with the signature metabolites of the catabolic pathways, were used as biomarkers to investigate androgen biodegradation in the largest sewage treatment plant in Taipei, Taiwan. Metabolomic analysis indicated that denitrifying bacteria in anoxic sewage adopt the 2,3-seco pathway to degrade androgens. Metagenomic analysis and PCR-based functional assay revealed androgen degradation in the anoxic sewage by Thauera via the action of 1-testosterone hydratase/dehydrogenase. On the other hand, bacteria in the aerobic sewage degraded androgens via the oxygenase-dependent 9,10-seco pathway, and Comamonas appears to be the key catabolic player. Our integrative ‘omics’ approach can be applied to the in situ investigations of microbial degradation of structurally complex compounds in which isotope-labeled substrates are not available.