Effects of oil contamination on microbial community and function in the La Crosse River Marsh

Water contamination by crude oil is a common issue, especially near railroad tracks. Crude oil contamination has been studied extensively in the past, but rarely with the focus on microbial communities in freshwater systems. This study aimed to identify the impact crude oil has on microbial community structure and function in water and sediment in the La Crosse River Marsh. This was done by measuring microbial methane and secondary production and analyzing the community structure in DNA extracted from water and sediment samples from control and oil amended mesocosms. Significant differences were not found between treatments for methane production. Secondary production differed significantly between treatments, but with conflicting results. Differences in microbial community composition were observed between the treatments on several phylogenic levels. Water samples from oil amended mesocosms collected at 48-hours showed a higher relative abundance of Flavobacteria and a lower relative abundance of Gammaproteobacteria than control mesocosms. Flavobacteriales, of the Flavobacteria class, and Clostridiales were the dominant orders in the microbial communities of the water column of the oil-amended mesocosms at 48-hours. Methylococcales became the most abundant order over time in water samples taken from control mesocosms but was not seen at a high relative abundance in samples from oil amended mesocosms. Sediment microbial communities were less influenced by the crude oil amendment than water communities. Sediment communities were dominated by deltaproteobacteria regardless of treatment. The only noticeable difference was that there was a higher relative abundance of Actinobacteria in samples from the oil amended mesocosms at 48-hours than in samples from control mesocosms. The changes in the microbial community composition show us that crude oil contamination does have important impacts on LCRM microorganisms, however even with these community shifts no definitive effect was seen on the microbial processes being tested