Microbial Degradation of Petroleum Hydrocarbons: An Overview

Abstract

Petroleum hydrocarbon contamination is severe in both terrestrial and aquatic environments. Hydrocarbon contamination affects both vertebrates and invertebrates in the environment under threat by oil spills. Several microbes participate in the decomposition of petroleum hydrocarbons (PH) under natural conditions. Microbes’ ability to remove PH has been studied extensively and exploited in the restoration of various spots affected by liquid hydrocarbon spills. Microbes involved in the decomposition of petroleum products consist of several bacteria and fungi. Almost 175 genera of bacteria, haloarchaeal bacteria, and eukarya are capable of degrading hydrocarbons into carbon dioxide and water. A consortium of microbes, rather than single species, is involved in degrading petroleum products as hydrocarbonoclastic microbes rarely function alone. Microbes isolated from terrestrial and marine environments contaminated with PH have proven to be excellent biodegraders of PH. Some of the Gram-negative hydrocarbonoclastic bacteria are Pseudomonas aeruginosa, P. fluorescens, Vibrio, Haemophilus spp., Marinobacter, Cycloclasticus, Pseudoalteromonas, Marinomonas, and Halomonas, whereas Mycobacterium spp., Rhodococcus spp., Paenibacillus spp., and Bacillus subtilis are some of the Gram-positive hydrocarbonoclastic bacteria. Hydrocarbonoclastic fungi include Phanerochaete chrysosporium, Bjerkandera adusta, Penicillium sp., Aspergillus sp., and Pleurotus ostreatus. It has been observed that bacteria, fungi, and microalgae are in close association while degrading PH, and it has been observed that the close association of bacteria and microalgae improves the degradation of PH. Enzymes produced by microbes which decompose PH comprise bacterial oxygenases and fungal exoenzymes such as lignin-modifying peroxidases like lignin peroxidases (LiPs), manganese peroxidases (MPs), and monocopper oxidases like laccases and epoxide hydrolases. Biodegradation of PH depends on various abiotic factors such as pH, temperature, oxygen, salinity, pressure, nutrients such as nitrogen and phosphorous, and their physical state. This review focuses on the microbes capable of degrading PH, the microbial processes involved in the degradation of PH, factors affecting the bioremediation, case studies involving bioremediation, and the recent strategies employed in in situ removal of PH.