Bacteria like their Oil Hot

Microbial processes are known to be involved in the biodegradation of petroleum hydrocarbons. The occurrence of hydrocarbon-degrading bacteria in polluted sites, their role in degradation and their ecological significance have been well documented. However, generalised trends of microbial degradation potential are not often elucidated due to the difficulties in comparing communities across varied systems. Moreover, high impact cases such as the Deep Horizon Oil Spill have seemingly received more attention in comparison to more chronically polluted sites. Bargiela et al. (2015) therefore conducted a large scale study in the Mediterranean and Red Seas to investigate drivers of bacterial biodegradation potential. Understanding the microbial degradation capacity in the the Mediterranean Sea is crucial as it has a continual, high level of oil pollution and a water turnover time of 70-90 years!

Bargiela et al. (2015) used an integrative approach to compare the influence of environmental, geographic and anthropogenic factors on seven chronically exposed oil polluted sites across the Mediterranean and one in the Gulf of Aqaba, Red Sea. Further to this, they compared these sites with meta-sequences obtained from the Deepwater Horizon oil spill, a site that was otherwise pristine. Initially, they characterized community composition through taxonomic barcoding. They then used a metagenomic approach to assess whether microbial communities would be predicted to have different degradation capacities in relation to environmental conditions. They were able to reconstruct a meta-network that specified with a confidence of at least 90%, the total relative abundance of catabolic genes involved with degradation reactions, and the number and identity of substrate pollutants or intermediates likely degraded. Subsequently, they conducted a metabolome-wide scan on sediment samples, using a combination of mass spectrometry with liquid chromatography separation, to assess whether chemical diversity would also affect microbial distribution and diversity.

A striking finding of this study was that in the chronically polluted, high temperature sites, although total bacterial diversity was lower, the catabolic diversity (i.e. pollutant degradation) was higher, than those of bacterial communities residing in lower temperature sites. Notably, they also found that bacteria in chronically polluted sites had an increased degradation potential than that of microbial communities in pristine sites, as assessed by the metagenomic analysis. Further to this, they found an increased abundance of genes encoding alkane degrading enzymes in the chronically polluted sites. The authors state that collectively, these findings suggest that microbial communities in warmer, chronically polluted sites may be more catabolically versatile and thus better able to respond to accidental oil spills than microbial communities found in pristine sites.

Understanding the role of temperature in catabolic activities of bacteria is crucial as oil pollution is occurring and will occur in parallel to global warming. Bargiela et al. (2015) provide correlative evidence suggesting that temperature may be used as a predictor of marine bacterial catabolic diversity. Previously, it was well known that temperature affects the rate of biodegradation (Leahy and Colwell, 1990), however it has not been established prior to this study the extent to which temperature, and other environmental parameters, regulate hydrocarbon metabolism. Future studies should explore this in more detail, by performing mesocosm-type experiments to directly investigate the effect of temperature on microbial composition and biodegradation capacity. Clearly, in a multi-stressor world, the combined effects of ocean warming, acidification, and other stressors are likely to be different to those of individual stressors. Therefore, future studies should aim to include multiple stressors in their experimental design.

Reviewed paper:

Bargiela, R., Mapelli, F., Rojo, D., Chouaia, B., Tornés, J., & Borin, S. et al. (2015). Bacterial population and biodegradation potential in chronically crude oil-contaminated marine sediments are strongly linked to temperature. Scientific Reports, 5(1). http://dx.doi.org/10.1038/srep11651

References:

Leahy, J., & Colwell, R. (1990). Microbial degradation of hydrocarbons in the environment. Microbiology And Molecular Biology Reviews, 54(3), 305-315.