Phylogenetic Analysis and Activity of Hydrocarbon-Degrading Bacteria Associated with the Marine Diatom Skeletonema costatum During a Simulated Oil Spill Experiment

Crude oil is one of the largest and most complex contributors of organic pollution in marine environments. The fact that our oceans are not covered in oil is, in part, due to the activities of hydrocarbon-degrading bacteria. Although relationships between phytoplankton and bacteria have been studied extensively, the ability of phytoplankton-associated bacteria to degrade components of crude oil has not been well-studied. Recent research has revealed an association between marine phytoplankton and bacteria that can degrade polycylic aromatic hydrocarbons (PAHs), a component of major concern in crude oil. This work expands on this research by investigating the effect of crude oil on the bacterial community associated with the marine diatom, Skeletonema costatum. Laboratory microcosms of S. costatum in seawater medium were incubated in the presence or absence of oil over a 64-day period. Growth of S. costatum was inhibited after the addition of oil, while total bacterial counts increased relative to the oil-untreated control. Quantitative PCR and pyrosequence analysis revealed members of the Marinobacter genus, which are known hydrocarbon-degraders, had significantly increased in abundance compared to the oil-untreated control. Notably, a significant increase in the abundance of Methylophaga species within the γ-Proteobacteria class was observed three days after the oil was added, representing over 80% of the total bacterial community in oil-contaminated microcosms. Despite substantial changes in the bacterial communities in contaminated microcosms, degradation of PAHs and alkane hydrocarbons was not found to be significant compared to killed controls. This result is likely due to low yields of bacteria on the growth substrates present after addition of oil. Overall, the results of this work have revealed new information on the identity and dynamics of bacteria associated with S. costatum during exposure to crude oil. These findings have taken us a step forward to better understanding the role that algal-bacterial associations might play in bioremediation processes at sea after an oil pollution event, for which further research on the relationship between phytoplankton and oil-degrading bacteria is needed.Master of Science in Public Healt