A new look on factors affecting microbial degradation of petroleum hydrocarbon pollutants

In recent years, there has been increasing concern over public health threat presented by introduction of petroleum hydrocarbon pollutants in environment due to anthropogenic activities to a greater extent and natural processes to some extent. Many countries all over the world are currently facing severe problem due to these pollutants as they are one of the persistent organic pollutants (POPs). Remediation of polluted sites by biodegradation is a viable option as conventional physico-chemical methods for remediation seems technically as well as economically challenging. Biodegradation is non-invasive and could be cost-effective in removal of petroleum hydrocarbon pollutants. It is considered as ultimate mechanism for pollutants removal. Immobilized microbial cells give advantage over free microbial cells to improve the survival and retention of the bioremediation agents in polluted sites. However, current biodegradation approaches suffer from a number of limitations, which include pollutant characteristics, poor capabilities of microbial communities in the field, lesser bioavailability of pollutants, growth conditions, etc. Understanding the factors affecting microbial degradation is of great research interest in present scenario. This review selectively examines and provides a critical view on bioavailability of the substrates, microorganisms in petroleum hydrocarbon pollutants degradation and the molecular techniques for their characterization, degradation mechanisms under aerobic and anaerobic conditions, commercially available bioremediation agents and factors affecting biodegradation of these pollutants. Role of genetically modified organisms and biodegradation of petroleum hydrocarbon pollutants by immobilized will also be discussed. (C) 2017 Elsevier Ltd. All rights reserved.