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      Recent studies in microbial degradation of petroleum hydrocarbons in hypersaline environments

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          Abstract

          Many hypersaline environments are often contaminated with petroleum compounds. Among these, oil and natural gas production sites all over the world and hundreds of kilometers of coastlines in the more arid regions of Gulf countries are of major concern due to the extent and magnitude of contamination. Because conventional microbiological processes do not function well at elevated salinities, bioremediation of hypersaline environments can only be accomplished using high salt-tolerant microorganisms capable of degrading petroleum compounds. In the last two decades, there have been many reports on the biodegradation of hydrocarbons in moderate to high salinity environments. Numerous microorganisms belonging to the domain Bacteria and Archaea have been isolated and their phylogeny and metabolic capacity to degrade a variety of aliphatic and aromatic hydrocarbons in varying salinities have been demonstrated. This article focuses on our growing understanding of bacteria and archaea responsible for the degradation of hydrocarbons under aerobic conditions in moderate to high salinity conditions. Even though organisms belonging to various genera have been shown to degrade hydrocarbons, members of the genera Halomonas Alcanivorax, Marinobacter, Haloferax, Haloarcula, and Halobacterium dominate the published literature. Despite rapid advances in understanding microbial taxa that degrade hydrocarbons under aerobic conditions, not much is known about organisms that carry out similar processes in anaerobic conditions. Also, information on molecular mechanisms and pathways of hydrocarbon degradation in high salinity is scarce and only recently there have been a few reports describing genes, enzymes and breakdown steps for some hydrocarbons. These limited studies have clearly revealed that degradation of oxygenated and non-oxygenated hydrocarbons by halophilic and halotolerant microorganisms occur by pathways similar to those found in non-halophiles.

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          Exposure to carcinogenic PAHs in the environment

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            Alkane hydroxylases involved in microbial alkane degradation.

            This review focuses on the role and distribution in the environment of alkane hydroxylases and their (potential) applications in bioremediation and biocatalysis. Alkane hydroxylases play an important role in the microbial degradation of oil, chlorinated hydrocarbons, fuel additives, and many other compounds. Environmental studies demonstrate the abundance of alkane degraders and have lead to the identification of many new species, including some that are (near)-obligate alkanotrophs. The availability of a growing collection of alkane hydroxylase gene sequences now allows estimations of the relative abundance of the different enzyme systems and the distribution of the host organisms.
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              Marinobacter hydrocarbonoclasticus gen. nov., sp. nov., a new, extremely halotolerant, hydrocarbon-degrading marine bacterium.

              On the basis of phenotypical characteristics and analysis of 16S rRNA sequence, a new species belonging to a new genus is described, and the name Marinobacter hydrocarbonoclasticus is proposed. This organism, isolated from Mediterranean seawater near a petroleum refinery, is a gram-negative, aerobic, rod-shaped bacterium. It grows at NaCl concentrations of 0.08 to 3.5 M and uses various hydrocarbons as the sole source of carbon and energy. Its DNA has a guanine-plus-cytosine content of 52.7 mol%. The 16S rRNA analysis shows a clear affiliation between M. hydrocarbonoclasticus and the gamma group of the phylum Proteobacteria. A close phylogenetic relationship appears among the species Marinomonas vaga, Oceanospirillum linum, Halomonas elongata, and Pseudomonas aeruginosa. Because of the impossibility of finding a single most closely related species, we suggest that this bacterium be assigned to a new genus, at least temporarily. The possibility of a revision of this status when new data appear is, however, not excluded. The type strain is M. hydrocarbonoclasticus SP.17 (= ATCC 49840).
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                Author and article information

                Contributors
                Journal
                Front Microbiol
                Front Microbiol
                Front. Microbiol.
                Frontiers in Microbiology
                Frontiers Media S.A.
                1664-302X
                23 April 2014
                2014
                : 5
                : 173
                Affiliations
                Department of Microbiology and Molecular Genetics, Oklahoma State University Stillwater, OK, USA
                Author notes

                Edited by: Antonio Ventosa, University of Sevilla, Spain

                Reviewed by: Ronald Oremland, United States Geological Survey, USA; Marco J. L. Coolen, Woods Hole Oceanographic Institution, USA

                *Correspondence: Babu Z. Fathepure, Department of Microbiology and Molecular Genetics, Oklahoma State University, 307 Life Sciences East, Stillwater, OK, USA e-mail: babu.fathepure@ 123456okstate.edu

                This article was submitted to Extreme Microbiology, a section of the journal Frontiers in Microbiology.

                Article
                10.3389/fmicb.2014.00173
                4005966
                24795705
                4f60f669-be0a-4cbe-a4f6-afad8578e987
                Copyright © 2014 Fathepure.

                This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

                History
                : 08 January 2014
                : 30 March 2014
                Page count
                Figures: 0, Tables: 5, Equations: 0, References: 103, Pages: 16, Words: 12474
                Categories
                Microbiology
                Review Article

                Microbiology & Virology
                hypersaline environments,biodegradation,oxygenated and non-oxygenated hydrocarbons,halophilic and halotolerant bacteria and archaea,molecular mechanism of degradation

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