Microbial Degradation of Pharmaceuticals

Abstract

In recent years, pharmaceuticals have surfaced as a novel class of pollutants due to their incomplete degradation in sewage treatment plants and their characteristic ability to promote physiological predicaments in humans even at low doses. Of the several physical, chemical and biological techniques studied for the degradation of drugs, microbial degradation is regarded preferential due to its energy intensive nature, lower ecological footprint as well as considerably lower production of toxic by-products. This chapter reviews the information on the microbial degradation of various classes of drugs including antibiotics, non-steroidal anti-inflammatory drugs, antihypertensives, antidepressants and anticancer drugs. Numerous bacterial, fungal and algal strains have shown substantial efficiency in degradation of various pharmaceuticals, mostly through co-metabolism using the drug as the secondary carbon source. A wide array of enzymes like dehydrogenase, hydrolase, oxidoreductase, oxidase, dioxygenase, monooxygenase, decarboxylase and many more are typically involved in the microbial degradation of pharmaceuticals. The ability of microbes to degrade pharmaceuticals is commonly attributed to their possession of functions analogous to mammalian CYP2C9 and CYP3A4. These isoforms of cytochrome P450 are majorly responsible for metabolism of drugs in humans. Hydroxylation by CYP450 is the most commonly reported initial step in the microbial degradation of drugs, and processes like decarboxylation, dehydrogenation, dechlorination, subsequent oxidation, demethylation, hydroxylation, cleavage of the ester group often constitute the degradation pathways. Although the efficiency and kinetics of degradation are known for most of the microbial strain, the degradation pathway is explained for very few because of the technical difficulties arising during the elucidation process. Though microbial degradation of pharmaceuticals is proving an attractive alternative in lab studies due to irrefutable advantages, the scaling up process is tedious and challenging due to several limitations with respect to microbial growth conditions and subsequent handling of microbial contamination.