The Deep-water Horizon oil spill is the second largest oil
spill in the history of the petroleum industry. On 20th April 2010,
high pressure oil and gas caused the deep-water drilling rig in the Gulf of
Mexico to explode, it is estimated that 4.1 million barrels of light crude oil
and natural gas leaked into the Gulf. To tackle this pollution 1.8 million
gallons of the chemical dispersant COREXIT was applied to the surface waters as
well as directly into the wellhead (1500m below surface level). During the
spill several research groups reported a plume of dispersed MC252 crude oil at
1100-1220mbsl (meters below surface level) at distances up to 35km from the
wellhead. It is thought to have formed as a reaction to the application of
COREXIT at the wellhead combined with the physical and chemical factors at 1100
mbsl depth.
The aim of this study was to investigate the succession of
the microbial community and the formation of microbial flocs in deep sea water
from the Gulf of Mexico. This aim was achieved by laboratory enrichments at
cold temperatures (5˚C) with high concentrations of the MC252 oil and COREXIT. There
were five enrichments tests using combinations of oil, COREXIT and FeCl₂ as
well as three control enrichment tests, with additional to study floc
formations. These investigations involved a source of uncontaminated water from
the depth of the recorded plume, MC252 oil from the Discovery Enterprise
drillship located directly above the wellhead and COREXIT 9500 dispersant which
was provided. The authors also aimed to select and isolate specific members of
the microbial community that are capable to degrade oil. The members were
isolated and identified from 20 day incubated enrichment samples, using 16S rRNA-based
identification and scanning electron microscopy. By monitoring the respiration
and degradation of oil and COREXIT during incubations the authors were able to
understand the pattern of succession and response of specific microbial
populations when exposed to high concentrations of high hydrocarbons. This
illustrates what happens in situations like the Deep-water Horizon oil spill or
from oil seeps on the ocean floor.
The different hydrocarbon fractions of MC252 oil in the deep-water
plume were previously found to be largely removed by a combination of
dispersion and microbial degradation by indigenous microbes in the deep sea. The
results showed that the bacterial communities adapted rapidly to the
introduction of hydrocarbons with sequences representative of first Oleispira, then Colwellia becoming dominant. The findings suggest that Colwelliaceae and Oceanospirillales played a predominant role in hydrocarbons in
deep sea; Colwellia could have a
competitive advantage in the presence of high concentrations of oil and
dispersant due to their ability to produce EPS and form flocs.
The deep-sea holds some oil degrading potential since there is
natural oil seeps, so it is interesting to see how application of dispersants
will affect this potential, especially in high concentrations. The fact that
this paper identified a dominant crude oil degrader (Colwellia) means it could
be utilised to perfect oil spill management. It would be interesting to compare
this study with future studies in the Gulf of Mexico to track the succession of
this species and if competition with Oleispira changes its dominance.
Baelum, J., Borglin, S., Chakraborty, R., Fortney, J.L.,
Lamendella, R., Mason, O.U., Auer, M., Zemla M., Bill, M., Conrad, M.E.,
Malfatti, S.A., Tringe S.G., Holman, H-Y., Hazen, T.C., Jansson, J.K., (2012), Deep-sea bacteria enriched by oil and
dispersant from the Deepwater Horizon spill, Environmental Microbiology,
Volume 14, Issue 9, September 2012, Pages 2405-2416
Hi Kathryn,
ReplyDeleteI’m sorry I think I might have got a little lost in your blog (maybe I’ve just got Monday morning syndrome). So they aimed to investigate the succession of the microbial community and the formation of microbial flocs in deep sea water from the Gulf of Mexico, and they were particularly interested in the deep-sea succession as this is where most of the Horizon oil ended up after dispersant addition. I follow that section, I think I’m a little lost at the results and the comparison between what had previously been found and what the reviewed study contributed to the previous finding. Is it just that previously it has been reported that deepsea microbes can degrade oil spills, and then the reviewed paper revealed the likely succession of microbes which we didn’t know about before? Please could you clarify this?
I’m also a little lost as to why Colwellia might be suspected to have a competitive advantage, and what the significance of this might be apart from the potential commercial bioremediation.
Robyn posted a blog about the Deepwater Horizon oil spill way back in October, she explained how molecular methods were used to identify the microorganisms which were active in the bloom and which functional genes were being expressed. The work she reviewed concluded the succession started with a community dominated by Oceanospirillales to domination by Colwellia and Cycloclasticus and eventually to methylotrophic bacteria, does this fit in with the results the paper you reviewed?
Many thanks,
Vicky
Hi Vicky,
ReplyDeleteThank you for your comment and sorry about the late reply,
Yes several reports noted that a variety of indigenous deep-sea microbes were the main source of degradation of the oil plume, but they also noticed a change in microbial community composition so this paper looked at the specific dominant microbes present and their part in the succession present particularly when exposed to high concentrations of hydrocarbons (e.g. oil spill).
Colwellia was said to have a possible advantage because of its ability to produce EPS (exopolysaccharide groups) and aggregate into flocs, these abilities were considered a key physiological mechanisms for communities to aggregate with oil droplets and conserve nutrients; this is shown really well in figure 5a. In regards to its competitive advantage the paper also mentions that the Colwellia sp have previously been shown to produce EPS under extreme conditions (i.e. low temperature, high pressure and low salinity), therefore Colwellia is likely to utilise oil in extreme environments than Oleispira sp.
A brief summary of the initial succession was mentioned that it was first Oleispira (Oceanospirillales), then Colwellia becoming dominant. Another microbe was also mentioned; Methylococcaceae was detected after 10 days of incubation, so there is a similarity to Robyn’s blog results. Unfortunately the only reference to Cycloclasticus is from a previous report from June 2010 so it does not follow the succession pattern exactly.
I hope I have helped, if not please let me know
Kathryn