Many studies have been conducted on the bioremdiation of
hydrocarbons, especially in light of large and damaging oil spills such as
Exxon Valdez and Deepwater Horizon. The utilisation of hydrocarbons by bacteria
has been a natural process for millions of years and they are present in almost
all natural environments. However, rates
of oil biodegradation are usually slow and consequently a wide range of toxic
and damaging effects can take place. There is therefore a need for a method to
enhance the rate of hydrocarbon biodegradation after oil spills. A mini review
by Ron and Rosenberg (2014) looked at and gave their opinions on how to enhance
bioremediation of oil spills in the sea.
Enzymes able to degrade hydrocarbons include the
membrane-bound oxygenases. It is essential for bacteria containing these
enzymes to come into direct contact with hydrocarbon substances. This, coupled
with the low solubility of hydrocarbons is the first major obstacle for
hydrocarbon degradation. Adhesion mechanisms are one strategy to increase contact
between the two. Bacteria already employ a number of different strategies such
as hydrophobic fimbriae, fibrils and outer membrane lipids and proteins. Another
strategy is the use of emulsifiers, many of which can have a bacterial origin.
These bioemulsifiers play an important role in enhancing the growth of bacteria
on hydrophobic substrates by increasing their solubility. They can also
regulate the attachment-detachment of microorganisms to and from surfaces.
However, the addition of some artificial emulsifiers, such as Corexit, can have
disastrous consequences. 700,000 gallons of Corexit was used as part of the
clean-up operation after Deepwater Horizon incident but instead had the effect
of increasing the toxicity of the oil 52 fold. Although both strategies have
the potential to help alleviate the threat crude oil spills on the marine
environment, more research will need to be conducted in this area. Perhaps
isolating or bioengineering a consortium of bacteria, which are both able to
easily adhere to and emulsify hydrocarbons, that could be applied to future oil
spill may negate many of the problems faced when artificial substances are
applied. Hydrocarbonoclastic bacteria may be of most use as they almost solely
utilise hydrocarbons and hydrocarbon degradation products as a carbon and
energy source. Therefore, if these bacteria were added to the environment, they
may only have a minimal effect on the ecosystem once crude oil levels had
fallen.
Another limiting factor for the marine bioremediation of
crude oil, as well as the marine environment in general, is the low levels of
phosphorus and nitrogen present. Approximately 150 g of nitrogen and 30 g of
phosphorus are consumed in the conversion of 1 kg of hydrocarbon to cell
material. Different fertilisers have been tried in attempt to increase the
levels of bacterial hydrocarbon degradation, however many problems have been
faced. Numerous fertilisers are water soluble so disperse quickly in open
systems and may also have toxic elements or increase the C:N ratio, therefore
many are deemed to be impractical. Uric acid, in contrast, displays several
properties that may allow it to be used to enhance the bioremediation of oil.
As well as having a low water solubility, it also adheres to hydrocarbons and,
being the major component of the waste product guano, it is widely available. It
has also been demonstrated to increase bacterial growth and crude oil
degradation significantly. Uric acid therefore has potential to be a useful
nitrogen and phosphorus fertiliser for oil spill treatment. However, increasing
nutrient availability in a system has to be treated cautiously. A large input
of nutrients may upset the natural balance through the proliferation of
opportunistic organisms. This may be especially prevalent if uric acid binds to
other organic compounds as well as crude oil hydrocarbons. Any use of uric acid
will have to be carefully researched and planned in order to limit any nutrient
excess after a clean-up from a crude oil spill has ended.
Ron, E. Z., & Rosenberg, E. (2014). Enhanced bioremediation of oil spills in the sea. Current opinion in biotechnology, 27, 191-194.
Hi Ben,
ReplyDeleteThis was my first article I reviewed for this blog (but don`t worry) I think it is such an interesting study that hasn`t given much attetion here. Do you know anything more about how much uric acid will be actually needed? I remember that the main problem we were wondering about was that guano (the bird poo) is over-exploited and brings big environmental problems with mining it. I was trying to find out how the authors can justify using it, however whether in this study or in one of the earlier ones on Uric acid I can`t find a reference. Tempted to email the authors! I`ll let you know if I find out :)
Thanks!
If only there was a resources where we can see all the papers already used! The paper they referenced only used small laboratory experiments to test their hypothesis and it was also performed at 30 degrees so I'm not sure how well their concentrations would scale to a larger system. Here's the link if you want to have a look: http://www.tandfonline.com/doi/pdf/10.1080/10889860600939492 .
DeleteGuano exploitation definitely is an issue (I bought a hut for a homeless penguin in SA because of this), it would be interesting to see what the authors say about the issue!