Date of Award

2021

Document Type

Open Access Master's Thesis

Degree Name

Master of Science in Biological Sciences (MS)

Administrative Home Department

Department of Biological Sciences

Advisor 1

Stephen Techtmann

Committee Member 1

Trista Vick-Majors

Committee Member 2

Gordon Paterson

Abstract

In this study, we investigated if significant differences existed seasonally in the microbial response to oil in the Straits of Mackinac, and if crude (Bakken) and refined (non-highway diesel) oil exposure had impacts on microbial community composition and hydrocarbon biodegradation across seasons using a microcosm-level experiment. Ambient microbial communities differed between seasons, with significantly enriched microbial groups present between all sample types except for between fall 23 ℃ and fall 4 ℃ microcosms. We found significantly different microbial communities between control samples and oil-amended samples in every season, but no significant community differences between either oil type. We found Amplicon Sequence Variants (ASVs) from the bacterial family Solimonadaceae were significantly enriched in all oil-amended microcosms compared to the control microcosms across seasons. We assessed oil breakdown across seasons and oil types over the course of five weeks through measuring CO2 production as a proxy variable for hydrocarbon metabolism using GC-FID. We observed a general trend of increasing respiration with oil amendment. No statistically significant differences in daily CO2 production existed between oil types across seasons or within seasons across oil types. These findings suggest that microbial communities in the Straits of Mackinac shift over the course of seasons even without oil amendment, and that freshwater microbial communities are compositionally and metabolically responsive to the presence of varying oil types.

Given the responsiveness of microbial communities in the environment to both crude and refined oil in our microcosm-level study, we aimed to investigate the feasibility of using microbes from environmental inocula to establish laboratory cultures for breakdown of other hydrocarbon sources such as alkenes. Our study goal was to quantify alkene breakdown in laboratory cultures and monitor changes in the microbial communities to draw associations to which microorganisms may play a significant role in alkene breakdown. We monitored breakdown using various metrics including CO2 production and found no significant distinctions in CO2 production across nutrient levels or inocula types. After GC/MS quantification of residual compounds we observed extensive biodegradation of all quantified compounds in the majority of samples. Microbial community diversity analyses throughout our experiment found that cultures initialized with environmental inocula from varying starting microbial assemblages converged to display significant overlap of bacterial families. Significantly enriched families across all inocula types included ASVs from families Xanthomonadaceae, Nocardiaceae, and Beijerinckiaceae. Distinctly enriched ASVs overlapping across treatment types restrained divergence of the overall communities. Overall microbial communities across nutrient levels within inocula types in Caspian Sea sediment and farm compost were significantly different. These results ultimately suggest that the microorganisms necessary to achieve alkene breakdown may be present in a variety of environmental microbial assemblages, and that they are strongly selected for under optimized conditions such as nutrient amendment.

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