A lot of
research has been done on the possibilities of using microbes to decontaminate
the marine pollution after an oil spill. Bioremediation appears to be no only
an efficient, but also an economically beneficial technique. This depends
however, on the bacteria used and the composition of compounds in the oil.
Often, the bacteria used are indigenous to the site of pollution and in
combination with each other instead of using single bacteria strains. Also,
four main fractions of oil can be distinguished regarding polarizability and
polarity: saturated alkanes, aromatics, resins and asphaltenes. Li et al. (2016) researched what bacterial
consortium would have the best biodegradation results in the Bohai Bay in
Chine, where a serious spill of crude oil occurred in 2011.
The study
consists of three main parts. First, oil-degrading bacteria are isolated and
identified from Bohai Bay. The identification was executed using 16s rRNA
sequences of the isolated strains. Five bacteria showed a significant
contribution to degrading the crude oil and were eventually used for further
research. They were named TBOC-1, TBOC-2, TBOC-3 and TBOC-4 and TBOC-5. Secondly,
the biodegradation of the hydrocarbons by the bacteria was analysed and the
five different strains were compiled into three consortia, of which the
remediation effectiveness was assessed in the last part. Consortium A consisted
of TBOC-4 and TBOC-5 on a 1:1 ratio, since these strains performed better on
biodegradation of saturated alkanes and because TBOC-5 degraded aromatics more
effectively compared to the other bacteria. (There was no significant degradation
shown for resins and asphaltenes.) Consortium A was therefore expected to have
complementary benefits. However, in the results it is shown that TCOB-2 has the
highest value for oil biodegradation of saturates, but it isn’t used in any of
the consortia. There is no reason mentioned for this, but it would be
interesting to get further details on this. Consortium B and Consortium C
functioned as comparisons and consisted of TCOB-1, TCOB-4, TCOB-5 and TCOB-1,
TCOB-5, respectively. Again, no reason was mentioned for using TCOB-1 in these
comparative consortia instead of one of the other three remaining strains.
The degradation
rates for consortia A, B and C, respectively, were 51.87%, 35.29%and 21.39%
after one week of incubation. The study shows an increase of 47.45% in the degradation
rate comparing bioremediation using a
single strain and consortium A, which implies synergy between TCOB-4 and
TCOB-5. What single bacterium they made this comparison with is not mentioned
however. The authors further compare their own findings to several other studies, with
the side note that the outcomes can not be compared directly, since the
parameters in the experimental set up differ per study. It might have been interesting
to show all these parameters and results per study in a table for a more
detailed comparison. Looking at the results of consortia B and C, it is
concluded that (1) it’s important to choose the most effective bacterial
strains in order to reach the highest possible degradation rate and that (2)
one should consider the possibility of bacteria strains limiting each other and
thereby reducing the growth of the most efficient oil degrading bacteria and
the overall biodegradation efficiency. In other words, using more strains of
bacteria would increase the chance of having the more effective ones amongst
them, but a higher amount of different bacteria increases the possibility of
competition to occur as well.
This study
gives an example of finding an effective construction for a bioremediating bacterial
consortium and highlight the necessity to focus on complementary advantages. The
main outcome is that the key to constructing these consortia is not the amount
of bacteria species used, but to use bacteria that show synergetic
bioremediation results. However, this statement seems contradictory to the
outcome formulated in the discussion part, where the quantity of bacteria did seem
to matter. The paper contains more of these obscurities, which gives a rather
unreliable appearance to it. Also, the findings don’t seem to be innovative and
it’s not clear how this research contributes to the scientific context.
Especially since a lot of similar research has already been done on this
subject. The authors do state however, that they’ve found a particularly
interesting combination of oil degrading bacteria with consortia A. Since it
only consists of two bacteria, it should be more economic and less ecologically
complex compared to earlier researched consortia consisting of more different
bacterial strains. All in all, I think this paper was an easy to read piece for
people who want more background knowledge on this subject, despite the
sometimes confusing or contradicting way in which some details are presented.
Article reviewed:
Adam, M. (2016). Biodegradation of marine crude oil pollution using a salt-tolerant bacterial consortium isolated from Bohai Bay, China. Marine pollution bulletin, 105(1), 43-50.
Hi Thryza,
ReplyDeleteAnother great post! I agree with your conclusive comments about the paper; the idea that a two bacteria could be utilised somehow to biodegrade Oil is quite exciting, especially if these are species which can be cultured. You mentioned in the beginning of the paper that many of these bacteria are 'indigenous'; surely this could mean that trans-locating or the introduction of these bacterial strains into areas containing oil (which they are not indigenous to) would render them useless, or at least less efficient at bioremediating? I know that it has highlighted how they have found individual strains, but surely they cannot rule out any miss-matches with new ecological niches? It would be interesting to see whether any future research papers try and conduct this in-situ (although - this would be difficult and therefore could take years!), and see if environmental variables influence the efficiency of these bioremediating bacteria?
Thank you,
Harriet