Fighting the DWH oil spill with exopolymers

The Deepwater Horizon (DWH) incident is one of the most tragic man-made disasters, which provoked major outcry from the public and the scientific community. Since then there has been a lot of research being done on the bacterial community involved in the oil degradation. One of the major processes that lead to the sedimentation of the oil to the seafloor was marine oil snow formation - oil droplets coagulated with transparent exopolymer particles into aggregates on the sea surface, which then rapidly sink to the ocean floor. The exopolymers, or extracellular polymeric substances (EPS), are biopolymers of high molecular weight secreted by microorganisms, which are primarily composed of proteins and carbohydrates (Passow et al. 2012). They have diverse functions for bacteria, and have recently being given major credit for influencing the fate of oil and chemical dispersants in the ocean.

Bacosa et al. (2018) researched into the identity of the key species involved in EPS production and oil degradation, and into the interacting factors in marine snow production. They succeeded in isolating nine bacterial strains, all belonging to the phylum Proteobacteria, which produce ETS in the presence of oil or Corexit as carbon sources. Six of the isolates were identified as members of the genus Alteromonas and the other three isolates were Thalassospira, Aestuariibacter, and Escherichia, with the last two not previously reported to be associated with oiled samples from the Gulf of Mexico following the DWH spill. Aggregate production varied with treatments and isolates, and the protein and carbohydrate content of the EPS differed across treatment and strain. The study showed that the presence of oil and Corexit generally increase the protein (but not the carbohydrate) content of EPS produced by bacteria. They displayed astounding results with one of the Alteromonas stains (W14) having an increase in protein content of EPS by 550-fold after the addition of Corexit. This suggests that the role of high protein is linked to boosted aggregation probably to protect the cells in disadvantageous conditions. The research also looked into the extracellular enzyme activity of the strains, reporting an enhanced activity in leucine amino-peptidase and alkaline phosphatase, when Corexit was added. A relationship between enhanced peptidase activity and the previously reported higher protein content of the EPS has been dismissed, because of the lack of increase in peptidase in some of the strains with enhanced protein content, including the W14 one. The study showed a typical oil degradation pattern with alkanes preferably degraded over the PAHs and managed to unravel the role of the Thalassopira in the picture, as evidence of their ability to degrade both alkanes and PAHs (2 and 3 rings) has been presented.  

The study of Bacosa et al. (2018) has introduced some new data on the bacterial community involved in oil degradation, and has brilliantly displayed the importance of EPS in the sedimentation of oil in the deep sea. Exopolymers are currently one of the hottest fields for research in marine microbiology, as impending findings on the tiny ecological niches of biofilms and aggregates require a broader understanding of the marine microworld.

Reviewed article:

Bacosa, H., Kamalanathan, M., Chiu, M., Tsai, S., Sun, L., Labonté, J., Schwehr, K., Hala, D., Santschi, P., Chin, W., Quigg, A. 2018. Extracellular polymeric substances (EPS) producing and oil degrading bacteria isolated from the northern Gulf of Mexico PLoS ONE 13(12): e0208406. https://doi.org/10.1371/journal. pone.0208406

References:

Passow, U., Ziervogel, K., Asper, V., Dierks, A. 2012. Marine snow formation in the aftermath of the Deepwater Horizon oil spill in the Gulf of Mexico. Environ. Res. Lett., 7 (2012), p. 11, 10.1088/1748-9326/7/3/035301