Steroidal estrogens, widespread in the environment, are contaminants of potential concern because exposure to these compounds can cause adverse impacts on aquatic life. Intensive research efforts have been undertaken in order to better understand the environmental occurrence of these compounds. In addition to physical/chemical reactions, biological processes - microbial biodegradation of steroidal estrogens - play a vital role in determining the fate and transport of these compounds in built and natural environments. This review summarizes the current state of knowledge on the microbiology of estrogen biodegradation. Aerobic and anaerobic estrogen-degrading microorganisms are phylogenetically diverse; they are mainly isolated from soils, activated sludge, dental plaque and intestines. Estrogens can be degraded via growth-linked and non-growth-linked reactions, as well as through abiotic degradation in the presence of selective microorganisms. Current knowledge on estrogen biodegradation kinetics and pathways is limited. Molecular methods are useful in deciphering estrogen-degrading microbial community and tracking the quantity of known degraders in bioreactors with different operating conditions. Future research efforts aimed at bridging knowledge gaps on estrogen biodegradation are also proposed.
