The threat of oil pollution through both natural seepage and
anthropogenic activities is a permanent danger to all marine biodiversity.
Numerous genera of marine bacteria, fungi and algae are responsible for the
degradation of the oil hydrocarbons, mainly due to the limited supply of
nutrients ordinarily available to them in seawater. This ‘self cleaning’
function has generated a lot of scientific interest over time because of its
practical applications in large oil spills. In the past, Biostimulation
(addition of nutrients) and bioaugmentation (addition of hydrocarbon-degrading
bacteria) have been tested in oil cleanup operations with varying degrees of
success.
Following previous research, this study chose the bacteria Alcanivorax borkumensis for
bioaugmentation trials, with the addition of other microorganisms to assist
with the degradation of heavy, aromatic compounds. 25 microcosms were set up in
duplicate, consisting of seawater from the island of Helgoland (some of which
was sterilised) and heavy fuel oil. A number of these microcosms were augmented
with the bacteria A. borkumensis (either
purified or with other microbes), others
with an absorptive sorbent made from textile or leather fibres (known as ‘X-Oil’),
and fertiliser was added roughly half
of them. These were incubated aerobically in the dark at 17oC (the
sample site temperature). 50ml of each microcosm was taken on a weekly basis
for analysis, and the deficit replaced with 50ml of seawater. Analysis included
DNA extraction and PCR, sequencing of DNA fragments and phylogenetic analysis.
The results of this study were numerous, but taken as a
whole, a few key points act as an effective summary. In all cases, A. borkumensis was found to break down
the oil pollutant in the samples. The speed of this decomposition was enhanced
significantly with the addition of fertiliser, which resulted in the
emulsification of the oil and therefore a larger surface area for increased
bioavailability. Biofilm formation was also detected in the nutrient-enhanced
samples due to these effects. The rate of oil degradation was again increased
in samples containing the X-Oil sorbents, which provided a good habitat to decomposers
and increased the emulsification speed in samples also containing fertiliser. Decomposition
in pure samples of A. borkumensis and
sterilised seawater was found be faster and more intense, but less thorough
than samples containing other organisms. DNA analysis showed a decrease in
microorganism diversity over time in all samples – a process that was sped up
with the addition of fertiliser, and even more so with both fertiliser and
X-Oil.
This study found that overall, A. borkumensis is an
extremely effective bacterium to use in the mitigation of oil spills for two
reasons:
-
It is proficient in the degradation of aliphatic
hydrocarbons
-
It naturally promotes the growth of other microorganisms
that can break down ‘heavier’ molecules, while inhibiting the rest
The authors of this paper conclude
by stating that the use of A.borkumensis combined
with the new X-Oil sorbents could become a useful tool for bioremediation in
future marine oil disasters. X-Oil does require further investigation despite
its success here however, as the use of leather and textiles in oil spill mitigation
is new and used for the first time in this experiment.
A review of Gertler C., Gerdts G.,
Timmis K.N., Yakimov M.M. and Golyshin P.N. (2009) Populations of heavy fuel
oil-degrading marine microbial community in presence of oil sorbent materials,
Journal of Applied Microbioligy, 107,
590-605
3 comments:
I don't understand why in science researchers always seem to be looking for one solution rather than another when it could simply require a combination of the two, as this study shows.
It makes sense that a combination of the addition of nutrients and the addition of hydrocarbon-degrading bactreria would have more of an effect on oil spills than one or the other.
In regards to this 'X-Oil', does it go into any detail as to why the bacteria degrade faster with it present. The only thing I can think it could possibly be is that it absorbs the oil and is therefore the oil is available in a much higher concentration in 'X-Oil' and so they degrade it more quickly.
Hi Jenny,
Really interesting review. Alcanivorax borkumensis sounds like an ideal 'spill cleaner'. You mentioned adding fertiliser enhanced the emulsification of the oil. Was it the fertiliser that broke up the hydrocarbon aggregates or was it due to increased bacterial activity as a result of adding the fertiliser? Also was the X-oil fibres used to absorb the oil or was it it simply used as a substrate for bacterial adhesion? Aliphatic compounds are essentially anhydrous and I was wondering whether there is a need for the oil to be modified before the bacteria can go to work or whether the bacteria are capable of breaking up the compounds without any assistance.
Thanks for your comments! Matt I agree with you. While one of these two components might make a degree of difference, the real magic comes from the combination.
I also agree with your suggestion. I got from the paper that the purpose of X-Oil is simply to absorb oil from the water and increase the surface area between the two. This gives the bacteria more space to proceed with decomposition, and it's this that increases the speed of degradation.
Mario - I think that the addition of fertiliser causes increased bacterial activity which would explain the increased speed of composition. I'm not sure about what actually caused the emulsification in those samples as the paper doesn't go into how this could happen, but as this occurred only in fertiliser-augmented samples, it's reasonable to assume that this has something to do with it. I've posted some further reading below - it's quite old but seems to suggest that fertiliser does aid the emulsification process as well as keeping the bacterial activity high.
Regarding your question about whether the oil would require modification before the bacteria can degrade it - the paper suggests that it doesn't, as these bacteria are naturally adapted to accommodate this. The only thing it did mention is that A. borkumensis is not able to completely degrade crude oil alone, as it cannot break down heavier molecules. I hope this helps!
reference: http://www.iosc.org/papers_posters/01893.pdf
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