Petroleum microbiology under extreme conditions

Abstract

Petroleum contamination of environmental matrices is a pervasive, global problem. Crude oil exploration, processing, handling and transport release significant amounts of petroleum hydrocarbons into the environment. Many petroleum compounds are known or suspected carcinogens, mutagens and teratogens and therefore, pose significant risks to human and ecosystem health. Petroleum hydrocarbon pollution constitutes an enormous challenge when areas with suboptimal environmental conditions are contaminated. This is because these regions are characterized by the occurrence of delicate ecosystems and because remedial efforts tend to be frustrated, owing to the unfavourable climatic and environmental conditions. Due to extensive petroleum exploration in some of these areas, petroleum hydrocarbon contamination occurs frequently, degrading the environment. Efficacious, sustainable abatement strategies are therefore, necessary to mitigate contamination. Over time, several treatment schemes and strategies for the replenishment of petroleum-contaminated sites have been designed, optimized and implemented. Many conventional techniques and technologies however, have significant limitations. This has prompted research into environmentally friendly and cost-effective clean-up alternatives. Bioremediation is an appealing option, which has been the subject of extensive research and has been adopted in many parts of the world because of its (comparative) low cost, minimal environmental impacts and public acceptance. Here, the general sources of petroleum hydrocarbons into the environment are explored as well as the effects of physicochemical and environmental factors on the transport, microbiology and overall fate of petroleum hydrocarbons in environmental matrices. The potential of petroleum hydrocarbon biodegradation under extreme environmental conditions is considered with an emphasis on the effects of unfavourable salinity, temperature, moisture, oxygen, nutrient, pressure and pH conditions. The roles of extremophiles in petroleum hydrocarbon biodegradation in extreme environments are also discussed. The influence of biosurfactants and the capacity of extremophiles to produce these under extreme environmental conditions are discussed as well as the relevance of bioaugmentation and biostimulation. Bioavailability, which influences the overall rate and efficiency of bioremediation protocols, is also considered.