Biodegradation is the utilisation of microbes to eliminate thousands of xenobiotic pollutants, including crude-oil, from the environment. Stimulating the growth of these microorganisms is a promising means of accelerating the detoxification of oil-polluted areas with a minimum impact on the ecological systems. Due to hydrocarbons being immiscible in water, growing the microbes on hydrocarbons has its difficulties. Many bacteria produce biosurfactants which overcome this problem; biosurfactants reduce surface tension, by accumulating at the interface, increasing surface area, which leads to increased bioavailability and subsequent biodegradation of the hydrocarbons.
Alkane hydroxylase is a key enzyme; it introduces an oxygen atom into the substrate. Based on phylogenetic analysis there are three main types of alkane hydroxylases; I, II and III, which degrade short, medium or long alkane chains respectively.
Oil pollution is particularly problematic in acute oil producing areas of the world, such as the Persian Gulf, Iran. Another marine environment in Iran which suffers from oil pollution, although not quite as bad, is the Caspian Sea. This paper aims to i) present bacterial strains present at these sites and evaluate them for production of biosurfactants and ii) analyse distribution of alkane hydroxylase genes in the isolated strains.
The authors isolated 25 bacterial strains, 11 of which (4 from the Caspian Sea and 7 from the Persian Gulf) showed higher growth rates on crude-oil. These were selected for further study.
The isolates were molecularly identified; only two were found to belong to the group obligate hydrocarbonoclasticus (OHCB), the remaining isolates were not related. The level of crude-oil biodegradation from these 11 species ranged from high (82%, 71% and 68%) to low (33% and 36%).
Each isolate degraded alkanes with a medium length (C12-18) to a greater extent than short chains (C9-11) and long chains (C19-25), this is because short-chained alkanes are toxic to most bacteria and long-chained alkanes are solid.
Results from ‘drop collapsing’ and ‘oil displacement’ tests indicate a direct relationship between cell-surface hydrophobicity and biosurfactant production and the emulsification activity and crude-oil biodegradation.
Results also showed that type II alkane hydroxylase enzymes were more prevalent in bacterial isolates from the Persian Gulf.
This paper concludes by saying that crude-oil-degrading bacteria have a high level of diversity and variability in biodegradation abilities. The use of these bacteria for bioremediation purposes will facilitate the better management of oil pollution in the Persian Gulf and Caspian Sea.
Overall an enjoyable read. I think this paper makes much sense; the isolates native to the problematic area were isolated and further researched to gain as much information from them as possible. It would be interesting to see what conditions these bacteria favour most, and then work on recreating these and possibility introducing them to polluted waters if a very bad pollution episode happens. This research not only needs to happen at all major oil producing areas of the world, but also in areas where oil spill migrate too.
A review of:
Hassanshahian, M., Emitiazi, G. and Cappello, S. (2012) Isolation and characterisation of crude-oil-degrading bacteria from the Persian Gulf and Caspian Sea. Marine Pollution Bulletin 64 7-12.
Alkane hydroxylase is a key enzyme; it introduces an oxygen atom into the substrate. Based on phylogenetic analysis there are three main types of alkane hydroxylases; I, II and III, which degrade short, medium or long alkane chains respectively.
Oil pollution is particularly problematic in acute oil producing areas of the world, such as the Persian Gulf, Iran. Another marine environment in Iran which suffers from oil pollution, although not quite as bad, is the Caspian Sea. This paper aims to i) present bacterial strains present at these sites and evaluate them for production of biosurfactants and ii) analyse distribution of alkane hydroxylase genes in the isolated strains.
The authors isolated 25 bacterial strains, 11 of which (4 from the Caspian Sea and 7 from the Persian Gulf) showed higher growth rates on crude-oil. These were selected for further study.
The isolates were molecularly identified; only two were found to belong to the group obligate hydrocarbonoclasticus (OHCB), the remaining isolates were not related. The level of crude-oil biodegradation from these 11 species ranged from high (82%, 71% and 68%) to low (33% and 36%).
Each isolate degraded alkanes with a medium length (C12-18) to a greater extent than short chains (C9-11) and long chains (C19-25), this is because short-chained alkanes are toxic to most bacteria and long-chained alkanes are solid.
Results from ‘drop collapsing’ and ‘oil displacement’ tests indicate a direct relationship between cell-surface hydrophobicity and biosurfactant production and the emulsification activity and crude-oil biodegradation.
Results also showed that type II alkane hydroxylase enzymes were more prevalent in bacterial isolates from the Persian Gulf.
This paper concludes by saying that crude-oil-degrading bacteria have a high level of diversity and variability in biodegradation abilities. The use of these bacteria for bioremediation purposes will facilitate the better management of oil pollution in the Persian Gulf and Caspian Sea.
Overall an enjoyable read. I think this paper makes much sense; the isolates native to the problematic area were isolated and further researched to gain as much information from them as possible. It would be interesting to see what conditions these bacteria favour most, and then work on recreating these and possibility introducing them to polluted waters if a very bad pollution episode happens. This research not only needs to happen at all major oil producing areas of the world, but also in areas where oil spill migrate too.
A review of:
Hassanshahian, M., Emitiazi, G. and Cappello, S. (2012) Isolation and characterisation of crude-oil-degrading bacteria from the Persian Gulf and Caspian Sea. Marine Pollution Bulletin 64 7-12.
4 comments:
Hi Rachel
I think this paper also highlights just how diverse microbes can be. It seems like every substance on earth has at least one microbe that will use it for a fuel source, even something as poluting as crude oil. I guess it is only fat after all.
Could I just clarify one thing please. I hope its not a silly question but you mention the biodegradation levels in %, is that the % of crude oil catabolised into other substances? If it is, do they say how long it took them to reach those percentages? :-)
Hi Rachel,
You mentioned the use of these microorganisms to clear up oil pollution, but I was wondering if the authors gave any indication of whether these bacteria could produce negative effects or outcompete other bacteria if they were introduced into a new environment? I find it all very interesting but I feel like humans always manage to create previously unseen problems but introducing non native species into new areas. It may be different with bacteria but you never know what native biochemical processes could be disrupted!
Hi, thanks again for your comments and questions.
Lee… When the authors talk about %’s the talk about the percentage of oil that was degraded, and it terms of how long it took them to reach the percentages it was one week. E.g. one of the 11 species degraded 82% of the oil within one week.
Arianna… The authors gave no indication of any possible negative effects that the introduction of these bacteria could cause, perhaps they just didn’t want to think of any, but it is of course worth considering if in the future the bacteria were to be introduced anywhere (although this seems a long way off).
Hi, thanks again for your comments and questions.
Lee… When the authors talk about %’s the talk about the percentage of oil that was degraded, and it terms of how long it took them to reach the percentages it was one week. E.g. one of the 11 species degraded 82% of the oil within one week.
Arianna… The authors gave no indication of any possible negative effects that the introduction of these bacteria could cause, perhaps they just didn’t want to think of any, but it is of course worth considering if in the future the bacteria were to be introduced anywhere (although this seems a long way off).
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