After a catastrophic oil spill, quickly remediating, removing, or cleaning the spilled oil can prevent damage to fragile coastal, open-ocean, and deep-water ecosystems and minimize public health and economic impacts for nearby human communities. Improved understanding of both natural and human-engineered processes that generate rapid remediation is therefore a top priority. Microbial biodegradation processes are thought to have played a substantial role in the surprisingly swift disappearance of oil and gas released into the Gulf of Mexico after the catastrophic Deepwater Horizon MC252 blowout. Although previous GoMRI-supported work investigated the composition of the coastal, open-open, and deepwater microbial communities that degraded this oil, much remains poorly understood regarding the impact of physical factors in heterogeneous ocean and coastal environments on the rate of microbial biodegradation. These factors include both steady ocean currents and intermittent flows due to turbulence; gradients in temperature, pressure, and salinity; and variations in local organic matter and soil content. These physical factors are expected to affect the ability of motile hydrocarbon-utilizing bacteria to move towards oil via chemotaxis, the directed motility of bacteria towards a chemical attractant, and hence the rate at which they degrade oil. Understanding the effects of physical factors on microbial biodegradation is additionally complicated by human-engineered strategies to clean spilled oil. For example, dispersants applied to break large oil slicks into smaller droplets can render oil more accessible to degradation by bacteria. Previous GoMRI-supported work identified the effects of dispersants on the viability of microbial populations, but their impact on microbial motility and attachment to oil-water interfaces remains poorly understood. Furthermore, dispersants alter the size of oil droplets and the surface tension and compliance of oil-water interfaces, which may in turn modulate microbial motility and chemotaxis. Hence there is a pressing yet unmet need to understand how (a) nearby liquid oil/liquid water or gaseous oil/liquid water interfaces, (b) fluid flow, and (c) dispersants affect microbial motility towards dispersed oil. Moreover, this need must be addressed for bacteria living in each type of ecosystem impacted by catastrophic oil spills.
The objective of this proposal is to elucidate the effects of oil-water interfaces on motility of marine bacteria in the initial stage in biodegradation, as microbes move towards and attach to dispersed oil. This proposal addresses Theme 2 in the GoMRI RFP-V, "Chemical evolution and biological degradation of the petroleum/dispersant systems and subsequent interaction with coastal, open-ocean, and deep-water ecosystems." The underlying idea driving the proposed work is that bacterial chemotaxis will enhance the rate of biodegradation and can be modulated by physical factors in the environment and by properties of oil-water interfaces. The four scientific questions to be addressed through this proposal are:
(1) How does bacterial chemotaxis affect the rate at which microbes degrade oil?
(2) How do the elevated pressures found in the ocean and in the Deepwater Horizon spill modify the motility, chemotaxis, and hydrocarbon utilization?
(3) How do dispersants alter microbial motility mechanisms and adhesion to oil-water interfaces during biodegradation?
(4) How do viscoelastic interfaces (characteristic of bacteria- and dispersant-coated oil drops) and flows (characteristic of the ocean environment) alter microbial motility?
These questions will be addressed by a team of four investigators with complementary expertise in microbiology, functional genomics, microscopy, interfacial science, high-throughput image analysis, mathematical modeling, and simulation. Using state-of-the-art experimental and computational methods, the team will address four hypotheses answering the scientific questions. The expected outcome of this plan of work is new understanding of how dispersed oil modifies bacterial motility and the efficacy of biodegradation, which in turn will address two ultimate goals that directly relate to the project objective and to GoMRI Theme 2. First, this plan of work will generate new insight into strategies for dispersant use that optimize microbial biodegradation rates, allowing spilled oil to be more rapidly cleaned. Second, this knowledge will contribute to improved models to predict the amount of oil degraded by microbes. Successfully achieving these goals will improve the ability to respond to and mitigate catastrophic oil spills in the Gulf of Mexico and hence the proposed work is strongly aligned with the mission of GoMRI.
Project Research Overview (2016):
An overview of the proposed research activities from the GoMRI 2016 Meeting in Tampa.
Direct link to the Research Overview presentation.