Microbial responses to marine oil spills: impacts of salinity, dispersant application and oil properties

Cao, Yiqi (2022) Microbial responses to marine oil spills: impacts of salinity, dispersant application and oil properties. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Marine oil spills can cause catastrophic impacts on ecosystems and human life. Natural attenuation by indigenous oil-degrading bacteria is one of the vital weathering processes that can result in oil mitigation. Various environmental factors, oil spill response options, and types of spilled oils would affect microbial physiologies for oil biotransformation. This thesis aims to uncover the effects of salinity, dispersant application, and oil property on microbial responses to oil biodegradation. To reveal the salinity effects on oil biodegradation, a halotolerant oil-degrading bacterium, Exiguobacterium sp. N4-1P, was tested as a model. The microbial eco-physiological strategy for salinity-mediated crude oil biodegradation was proposed for the first time. The impacts of dispersant application on oil biodegradation under diverse salinities were also evaluated, which showed that dispersant addition could override the oil biodegradation barriers at hyper-salinities primarily through enriching cell abundance. Increased production of unconventional heavy crude oils has led to increased marine transportation and spill risks. The effects of dispersants on the natural attenuation of the dilbit (diluted bitumen) within microbial communities over time were comprehensively evaluated using a metagenomic/metatranscriptomic approach. We found that dispersant has short-term inhibiting effects, but over the long term, its effects are insignificant. In addition, magnetic nanoparticles decorated bacteria (MNPB) were developed for responding to a simulated heavy crude oil attachment. A strategy named “access-dispersion-recovery” was proposed, and it led to enhanced mitigation of heavy crude oil pollution. The responses of an Alcanivorax species isolated from the North Atlantic Ocean for degrading alkanes and plastics were also studied. Experimental results indicated that the well-recognized obligate alkane-degrader Alcanivorax tied to ocean hydrocarbon cycles could also strongly degrade plastics. The existing biogeochemical processes involved in hydrocarbon biodegradation may aid in the ecosystem’s resilience to the impact of the new anthropogenic plastic-based carbon. The outputs of the thesis could advance the understanding of sophisticated marine crude oil biodegradation processes, generate potentially promising remediating tools for oil spill responses, provide new insights into marine hydrocarbon degradation, and benefit decision-making for adopting oil spill responding options.

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