Microbial degradation of petroleum hydrocarbons

Highlights

• Petroleum hydrocarbon pollutants are classified as persistent organic pollutants.

• These pollutants pose adverse effects on human and environmental health.

• Combat environmental pollution due to hydrocarbon pollutants is big issue for scientists.

• Biodegradation is an eco-friendly and economic method to control hydrocarbon pollution.

• Oleophilic microorganisms can be used for oil spill bioremediation.

Abstract

Petroleum hydrocarbon pollutants are recalcitrant compounds and are classified as priority pollutants. Cleaning up of these pollutants from environment is a real world problem. Bioremediation has become a major method employed in restoration of petroleum hydrocarbon polluted environments that makes use of natural microbial biodegradation activity. Petroleum hydrocarbons utilizing microorganisms are ubiquitously distributed in environment. They naturally biodegrade pollutants and thereby remove them from the environment. Removal of petroleum hydrocarbon pollutants from environment by applying oleophilic microorganisms (individual isolate/consortium of microorganisms) is ecofriendly and economic. Microbial biodegradation of petroleum hydrocarbon pollutants employs the enzyme catalytic activities of microorganisms to enhance the rate of pollutants degradation. This article provides an overview about bioremediation for petroleum hydrocarbon pollutants. It also includes explanation about hydrocarbon metabolism in microorganisms with a special focus on new insights obtained during past couple of years.

Introduction

Petroleum hydrocarbons are important energy resource and a raw material for various industries. Increasing demand for petroleum products in day to day life may cause their scarcity and increase their cost as suitable alternatives are still not found (Varjani et al., 2015, Varjani and Upasani, 2016b). Petroleum hydrocarbon pollutants are recalcitrant compounds and are classified as priority pollutants (ATSDR, 2011, Costa et al., 2012). Anthropogenic activities such as industrial and municipal runoffs; effluent release; offshore and onshore petroleum industry activities as well as accidental spills cause petroleum hydrocarbon pollution. This pollution affects the environment and pose direct or indirect health risk to all life forms on planet earth (Margesin and Schinner, 2001, Deppe et al., 2005, Souza et al., 2014, Sajna et al., 2015). Marine environment is considered as the ultimate and largest sink for petroleum hydrocarbon pollutants, therefore it is necessary to combat pollution problem (Ron and Rosenberg, 2014, Varjani and Srivastava, 2015). Remediation of hydrocarbon pollutants and enhanced oil recovery are two main burning issues of petroleum industry (Sajna et al., 2015, Varjani et al., 2015, Varjani and Upasani, 2016a, Varjani and Upasani, 2016c). To understand the scope and strategies of pollutant bioremediation it is essential to first understand properties of crude oil, environment of concern, fate of oil in that environment, mechanisms of crude petroleum biodegradation and factors that control its rate (Atlas, 1981, Boopathy, 2000, Varjani, 2014).

Mainly petroleum is constituted by saturates/paraffins, aromatics, resins and asphaltenes (Varjani, 2014). Crude oil is a mixture of variety of simple and complex hydrocarbons which are degraded by several indigenous microorganisms, each capable of breaking down a specific group of molecules (Zanaroli et al., 2010). Sugiura et al. (1997), and Ghazali et al. (2004), have reported that same compound in different crude oil samples was degraded to different extents by same organisms/consortium, the reason could be bioavailability of a particular compound in a crude oil sample and not it’s chemical structure.

Bioremediation of crude oil polluted sites is often limited due to poor biodiversity of indigenous microflora and/or scarcity of native specialized microbes with complementary substrate specificity required for degrading different hydrocarbons occurring at polluted site (Ron and Rosenberg, 2014). There are various reports available on metabolic versatility of mixed cultures that have demonstrated superiority of mixed cultures to pure cultures to utilize hydrocarbon pollutants in petroleum crude as sole carbon source (Cerqueira et al., 2011, Das and Chandran, 2011, Varjani et al., 2013). Bacterial and fungal co-culture(s) have shown improved degradation rates of diesel oil and many polyaromatic hydrocarbons (PAHs) when checked in laboratory conditions (Li et al., 2008, Wang et al., 2012, Varjani and Upasani, 2013). Hence catabolic cooperation between different microbial groups during biodegradation is very important (Atlas, 1981, Varjani et al., 2015).

The intent of present review is to expand bioremediation scope of petroleum hydrocarbon pollutants. It includes consideration of toxicity and fate of petroleum hydrocarbons in environment. It also discusses factors affecting biodegradation rate, microbial metabolism of petroleum hydrocarbon pollutants, pathways for hydrocarbon pollutants degradation and types of bioremediation technologies as well as processes.