Eating Oil… Not as Crude as You’d Think!

Due to sea water being poor in biogenic mineral nutrients, carbon and other sources of energy, marine microbial communities have adapted to survive in such oligotrophic conditions. However, when there is a large influx of nutrients, for example in the case of an oil spill, some microbes find it very stressful and difficult to cope with. On the contrary, other microbes can rapidly adapt to these situations and thrive, thus out-competing their competitors. An example group of organisms which are able to do this are the Obligate Hydrocarbonoclastic Bacteria (OHCB), containing organisms from the genera Cycloclasticus, Thalassolituus, Oleiphilus, amongst others. OHCB are able to grow in these short period, high nutrient conditions, and rapidly deplete them. Once depleted, the OHCB become inactive, making them potential organisms used in bioremediation techniques.

Having observed promising results of bioremediation in similar studies, the authors of this paper decided to look at the changes in marine flagellate and ciliate communities in a controlled mesocosm experiment. They did this by filling 2 500l mesocosms with seawater, followed by the addition of 2.5l Bunker C heavy fuel oil. Samples were taken from the mesocosms throughout the duration of the experiment, and the microbial communities within these were identified.

The results of this experiment revealed that there was an increase in the numbers of marine protozoa. This protozoan growth was continually observed throughout the experiment in both mesocosms. There were two initial blooms, where protozoan numbers fluctuated between 300 and 3000 cells per millilitre. Protozoa development paralleled the depleting levels of oil, oil emulsion and biofilm aggregates observed in the mesocosms. The majority of protozoa which were observed in the mesocosms were in the Ciliatia. Cilliates are commonly found in experiments involving oil degradation as they are well adapted to graze on oil-degrading communities. The ciliates in this study were predominantly Scuticocilitia,

Finally, in the second part of this experiment, an abundance of marine fungi  and yeasts were observed. This was reported as the ability for Candida yeasts to grow on gas oil has been acknowledged for several years, and a high number of these and related species are efficient degraders of fatty acids, polyaromatic hydrocarbons and oil. Marine fungi and yeasts have been used on a large scale for single cell protein production from oil paraffins.

I believe that this paper gives a good insight into marine microbiological degradation of oil spillages. I think, however that the difference between a controlled mesocosm experiment and a spill in the ocean could show large differences in results. I understand that studies have been carried out in controlled, closed-water environments, however this could still show different results than if the same were to be tested at sea.

Gertler, C., Näther, D. J., Gerdts, G., Malpass, M. C. & Golyshin, P. N. (2010) A Mesocosm Study of the Changes in Marine Flagellate and Cilliate Communities in a Crude Oil Bioremediation Trial. Environmental Microbiology. 60: 180-191.