Testosterone is a naturally occurring steroid. It has a variety of medical applications, including hormone replacement therapy and treatment of osteoporosis ([http://www.ncbi.nlm.nih.gov/pubmed/16841196|Gao et al., 2006]), and is also widely used as a feed additive in concentrated animal feeding operations (CAFOs) ([http://www.ncbi.nlm.nih.gov/pubmed/15843648|Lorenzen et al. 2005]). Sewage treatment effluent, manure spread onto agricultural fields, and pulp and paper effluent can contain high levels of androgens such as testosterone, which have the potential to contaminate freshwater supplies ([http://www.ncbi.nlm.nih.gov/pubmed/15843648|Lorenzen et al. 2005]). A U.S. Geological Survey study found concentrations of testosterone as high as 0.214 micrograms/L in stream water ([http://www.ncbi.nlm.nih.gov/pubmed/11944670|Kolpin et al., 2002]). The EPA reporting level for this steroid, which is classified as an Endocrine Disrupting Compound (EDC), is 0.005 micrograms/L. Several bacterial species can utilize steroids such as testosterone as a sole carbon source, the best-studied being Nocardia restrictus and Comamonas testosteroni. [http://www.ncbi.nlm.nih.gov/pubmed/16151114|Horinouchi et al. (2005)] have documented the degradation pathway used by Comamonas testosteroni strain TA441. The pathway begins with aromatization of the A ring, followed by metacleavage. The product is then cleaved again to produce 2-hydroxyhexa-2,4-dienoate and 9,17-dioxo-1,2,3,4,10,19-hexanorandrostan-5-oate. i The degradation pathway for the latter product is not yet known, although it may be broken down via mechanisms similar to those found in fatty acid metabolism ([http://www.ncbi.nlm.nih.gov/pubmed/15474469|Horinouchi et al., 2004]). The former compound is converted to 4-hydroxy-2-oxohexanoate, which is probably broken down to pyruvate and propanal ([http://www.ncbi.nlm.nih.gov/pubmed/16151114|Horinouchi et al., 2005]).