Dissolved
Organic Matter (DOM) is one of the largest and least understood pools of carbon
in the ocean, and ~10-25% of the total oceanic DOM is composed of biopolymers.
A large proportion of DOM is produced from the synthesis and release of exopolysaccharides
(EPS) from bacteria and eukaryotic phytoplankton. This has led to research into the potentially
significant role of EPS, particularly in bacteria, in the degradation of
hydrocarbon pollutants in the ocean. There has been much interest in the fate
of the oil released following the explosion and sinking of the Deepwater Horizon
oil rig in the Gulf of Mexico in 2010, the worst accidental marine oil spill in
the history of the oil and gas industry. The fate of the oil from the ecological
disaster is poorly known, but Gutierrez et al. stress the importance of
understanding the capacity of EPS produced by marine bacteria to affect the
dissolution of aromatic hydrocarbons to enhance the bioavailability of these
compounds for indigenous microbial communities and hence the rate of
degradation.
EPS-producing
bacteria enriched during the oil spill were thought to have contributed to the formation
of abundant oil aggregates on the surface and within deep water oil plumes, and
the authors demonstrated this enrichment both in laboratory experiments and in
the field. This study used one type of EPS-producing bacteria, the Halomonas species strain TG39, as a
model to predict the potential influence of EPS on the oil, which was collected
from surface waters during the active phase of the spill. This strain produces
large amounts of EPS which display amphiphilic, or biosurfactant-like, properties,
and can lead to the emulsification of aromatic hydrocarbons, crude oils or
refined petroleum products by interacting with hydrophobic substrates on their
surfaces and solubilising them to enhance their biodegradation.
An
additional analysis of pyrosequence data from surface water samples collected during
the spill revealed other distinct Halomonas
strains which could produce EPS. Some of these strains had high (97%-100%) 16S
rRNA sequence identity to strain TG39. Clusters of other EPS-producing bacterial
communities, such as Alteromonas, Colwellia and Pseudoalteromonas, were also enriched in surface and deep waters, and
could also emulsify the oil and form aggregates, which may have supplemented
the bioavailability of EPS in the Gulf. They also used a roller bottle
incubation experimental design with one of the other Halomonas isolates, TGOS-10, which exhibited an independent ability
to emulsify the oil, as the aggregates directly formed on the extracellular
cell surface of the strain.
Evidence from
the results showed that the EPS produced by Halomonas
species strain TG39 can facilitate the dissolution of poorly-soluble
aromatic hydrocarbons, which enhanced the bioavailability to indigenous
populations of microorganisms present during the active phase of the spill,
particularly in the surface waters. The enrichment of EPS-producing bacteria,
together with their capacity to produce amphiphilic EPS, is likely to have
contributed to the eventual removal of the oil and to the formation of oil
aggregates.
The authors
focus on the enrichment and dominance of EPS in the Halomonas strain to influence the degradation of the oil in the
surface waters, as well as other EPS-producing bacteria in the deep water oil plumes,
but it would be interesting to see whether the rate of degradation differs in
the surface waters compared to the deep water plumes and whether it is based on
the level of enrichment alone. In addition, as this experiment was carried out
during the active phase of the oil spill, further research should look at the after-effects
to see how the abundance of the DOM pool changed once the oil had been degraded,
and the effect it may have had on the carbon cycle in this region of the Gulf.
Gutierrez, T., Berry, D., Yang, T., Mishamandani, S.,
McKay, L., Teske, A., and Aitken, M.D. (2013) Role of Bacterial
Exopolysaccharides (EPS) in the Fate of the Oil Released during the Deepwater
Horizon Oil Spill. PLoS one, 8 (6),
e67717
I wonder if EPS could ever be mass produced using biotechnology and be dumped onto oil spills to facilitate faster breakdown. I bet its emulsifying properties could be useful in cleaning up other pollution events.
ReplyDeleteI thought this as well when reading through the discussion...these EPS-producing bacteria seem to be enhancing the effect of local endemic microbial species to speed up the process of degradation, so it is a natural occurrence that doesn't involve introducing artificial or foreign chemicals into the environment that could have equally negative, harmful impacts on the marine life. I think this could potentially catch on in the future, but the current research is trying to understand the diversity and function of these bacteria in more detail before they can do this.
ReplyDeleteThe paper I reviewed on oil-degrading bacteria says that bacteria could potentially degrade hydrocarbons into compounds with an even higher toxicity, do you think that with enhancing the effect of these bacteria it could possibly create another problem for organisms?
ReplyDelete