Denitrifying bacteria: Physiological response to hydrocarbons

Abstract

Petroleum pollution has short-term and long-term deleterious effects on the vulnerable marine ecosystem, including deep-sea, coastal and estuarine systems and is evidently a global concern. Various approaches involving biodegradation of hydrocarbons by natural populations of microorganisms are being employed to counteract petroleum contamination. Denitrifying bacteria are ubiquitous, heterotrophic and capable of breaking down a wide range of aliphatic, aromatic and polycyclic hydrocarbons. Their unique flexibility to switch between aerobic and anaerobic respiration can be efficiently capitalized upon in the bioremediation of hydrocarbons. The coastal/estuarine systems of the Mandovi and Zuari estuaries in Goa harbour a prolific population of hydrocarbon-utilizing denitrifying bacteria attributed to the influx of nutrients, including nitrate and hydrocarbons. Studies on two potential isolates TSB.MJ10 and TMR2.13, isolated from mangrove and sand dune sediments of Goa and identified as Pseudomonas nitroreducens and Pseudomonas aeruginosa, respectively, elucidate the various adaptive mechanisms undertaken by denitrifying bacteria in response to hydrocarbons. Hydrocarbons have a prominent influence on the important physiological processes, including growth, morphology and denitrification. Denitrifying bacteria produce various extracellular metabolites like pigments, biosurfactants and bioemulsifiers to facilitate their growth and metabolism in the presence of these hydrocarbon pollutants. These mechanisms can be critically analysed for developing effective strategies for bioremediation of hydrocarbons.