The importance of bacteria for biodegradation of petroleum is well described for contaminated seawater and coastal soils, but very little is known about the role of symbiotic plant bacteria in degrading petroleum. Endophytes are bacteria and fungi that live as symbionts within plant roots, stems and leaves. These symbionts are closely associated with the plant and some endophyte species serve the dual purpose of promoting plant growth and degrading petroleum inside of plant tissues. In an extreme environment such as a salt marsh, where oxygen is limited in soils, plants may be especially dependent on endophytic bacteria for resilience to stress and to respond to petroleum contamination.
Preliminary research since the Deepwater Horizon (DWH) oil spill has shown that when coastal grasses are contaminated with petroleum, the bacterial communities in their tissues incorporate more taxa with known roles in biodegradation. This preliminary work has led to the hypotheses driving this proposal: that endophyte communities inside of coastal plants will shift to incorporate and amplify endophytic bacteria that are tolerant to petroleum and can biodegrade it inside of plant tissues, and that plant delivery of oxygen and endophytic bacteria to polluted soils will hasten the chemical evolution of petroleum. Addressing these hypotheses at the mechanistic level involves describing the transport mechanisms and the catabolic activities of bacteria with respect to petroleum inside of plant tissues and at the interface of grass roots and the rhizosphere. These processes are not well characterized, particularly in saline marshes. Such a knowledge gap is a problem because it prohibits a mechanistic understanding of how grasses, symbiotic bacteria and polluted soil interact, and thus slows the development of remediation tools that use plant-delivered, naturally occurring bacteria to clean up polluted soils.
The overall goal of the proposed research is to develop a mechanistic understanding of plant bacterial symbioses in relation to petroleum/dispersant pollution in saline marshes. The proposed work will characterize the transport, fate and catabolic activities of bacterial communities in petroleum-polluted soils and within plant tissues. The project focuses on Spartina alterniflora (smooth cordgrass), the foundational grass species within salt marshes along Atlantic and Gulf coasts. The specific goals are (1) to use next-generation genomic technology for characterizing the taxonomy and function of microbial communities inside of S. alterniflora tissues and in the rhizosphere, while relating these communities to the chemical evolution of crude oil constituents in plant tissues and in soil; and (2) to use new visualization and computational modeling approaches for investigating the biomechanical and chemical influences on bacteria movement at the interface of roots and soil to mechanistically relate bacterial chemotaxis to the presence of petroleum, dispersant, oxygen and root exudates. The proposed research goals directly address GoMRI research theme two, as each ultimately relates plant-symbiont interactions to the chemical evolution and biodegradation of petroleum and dispersants in coastal ecosystems. Pursuing these goals will advance understanding of key processes that occurred in the DWH spill and may occur in future spills.
The outcomes of the proposed research will include (1) a deeper knowledge of the functional genomics of petroleum degradation and uptake of petroleum into plants, (2) the first descriptions and computational models for the biomechanical and chemical aspects of bacterial movement at the root: rhizosphere interface in response to petroleum and dispersant, and (3) the first determination of how plant-endophyte symbioses influence the fate of petroleum in marsh ecosystems. Developing a mechanistic understanding of plant-symbiont-petroleum interactions could provide a foundation for the development of remediation tools using naturally occurring plant-bacteria combinations. Such strategies are being developed in other ecosystems but have not yet been extended to include coastal plants in the Gulf of Mexico (GoM), where there is a persistently high threat of petroleum contamination.
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.