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 plant symbionts for degrading petroleum constituents that are deposited on and in leaves. 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 may serve the dual purpose of promoting plant growth and degrading petroleum both on or inside of plant tissues. We have been studying the effects of the Deepwater Horizon oil spill on endophytes of Spartina alterniflora, the key species along coasts where oil was deposited and persists in the marsh soil. We are currently testing the hypothesis that endophyte communities inside of coastal plants will shift to incorporate and amplify endophytic bacteria and fungi that are tolerant to petroleum and can biodegrade it inside of plant tissues. We use a combination of field, laboratory and greenhouse studies, relating microbial community composition to the weathering ratios of polyaromatic hydrocarbons (PAH) and to plant growth.
Results/Conclusions
We have found that even six years after the oil spill, leaves of S. alterniflora from field sites show altered foliar endophyte communities, with losses in diversity where oil pollution was greatest. In contrast, there were fewer changes observed in below-ground plant symbionts. When we sampled three years after the spill, there were significantly lower abundances of fungi in leaves, compared to bacteria which only showed shifts in community composition. As our sampling sites varied in magnitude of the oil deposition along the coast, we also observed significant site differences with respect to endophyte community composition. Our ongoing work in the greenhouse is geared toward understanding the ultimate effects of PAH and endophyte community shifts on plant growth.