Bioremediation of Crude Oil Spills Impacts Microbial Communities and the Magnetic Susceptibility of Sediments
Beaver, Carol L.; Williams, Anja; Atekwana, Estella; Aal, Gamal Abdel; Mewafy, Farag; Slater, Lee; and Rossbach, Silvia
Western Michigan University United States.
A worldwide increase in the production, shipment, and storage of crude oil has led to an increase in oil spills, and efforts to physically remove this oil from the environment are often insufficient. As a result, hydrocarbon contamination that is not eliminated by suction, excavation, or by dispersants remains in the water and sediments to be degraded by microbes. Initially, the bioremediation of oil occurs aerobically, but as oxygen is depleted, microbes must switch to alternate electron acceptors. Gradients of terminal electron acceptors form over time, which in conjunction with the toxic properties of oil, have an effect on the microbial community composition at hydrocarbon-impacted sites (1). These gradients of terminal electron acceptors also change the geochemical and geophysical properties of these sediments. Eventually, iron-reducing and methanogenic communities predominate at the center of oil plumes, where iron-reducing bacteria may precipitate magnetite (2). Thus, we are investigating if magnetic susceptibility measurements (MS) of crude oil-contaminated sediments can be used to monitor the production of magnetite resulting from bioremediation. For our experiments, we obtained one core retrieved from the center of an oil plume and one from an uncontaminated area downstream of an oil plume at a crude oil spill site in Bemidji, MN. MS measurements were taken in the wells remaining from the cores. Total DNA was extracted from samples taken from the cores, and 16S rRNA gene high throughput sequencing was used to assess the microbial communities. Results showed that microbial communities shifted towards methanogenic and fermenting populations in the oil plume at the water table, unlike the uncontaminated core, which did not. Interestingly, the highest peaks in MS were measured in the contaminated core around the water table, corresponding to the oil plume and the methanogenic zone. The peaks in MS may have been due to magnetite formed from iron reduction that occurred prior to methanogenesis, or from iron reduction that is occurring concurrently with methanogenesis. In either case, MS was higher where hydrocarbons are being degraded. Thus, we conclude that MS may be used to monitor bioremediation processes at crude oil spill sites.