Doctoral Dissertations

Date of Award

8-2024

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Life Sciences

Major Professor

Terry C. Hazen

Committee Members

Larry D. McKay, Christopher W. Warren, Paul E. Abraham

Abstract

The Caspian Sea is the world’s largest landlocked saline lake positioned between Europe and Asia and for its historic and large-scale oil reserves. These vast oil reserves have led to the development of an intricate network of pipelines, and drilling operations causing the environmental deterioration of the waterbody. Drainage from surrounding river basins brings an influx of pollutants from residential, industrial and agricultural origins which further compounds this issue. The endorheic nature of this waterbody causes the retention and accumulation of these pollutants, ultimately reducing water quality.

The increased nutrient input has steadily intensified eutrophication in this waterbody resulting in hypoxic conditions in deeper, colder waters, creating an oxygen gradient. With both temperatures and dissolved oxygen decreasing around 50m in this waterbody, ee sought to capitalize on the highly adaptable nature of microorganisms to respond to environmental stressors. The unique temperature and oxygen stratification in this brackish environment presented an opportunity to explore the potential of the biodegradative capability of the indigenous microbial community. We hypothesized that the Caspian Sea microbial community possess different metabolic capabilities to degrade crude oil as they adapted to declining oxygen concentrations and temperatures with increasing depths.

Microcosms were assembled with surface waters (25m) and deep waters (350m) from Caspian Sea and 60ppm of native crude oil and observed over 115 days to represent oxic and hypoxic conditions respectively. Surface water microcosms were incubated at 28ºC and aerated while deep water microcosms were incubated at 8ºC under anaerobic conditions to simulate the temperature and oxygen extremes along the gradient as we tried to trigger the indigenous community’s response to crude oil.

A 16S rRNA analysis was conducted to determine taxonomic abundances, gas chromatography coupled with mass spectrometry was conducted to confirm degradation of hydrocarbon fractions in crude oil and metagenomic analysis was conducted to determine functional potential of observed taxa. These methods showed evidence of degradation of hydrocarbon fractions in both oxic and hypoxic conditions. The metabolic diversity of taxa varied in our differing oxygen conditions as well as the observed taxa. To further explore the potential diversity of hydrocarbon degradation in these microcosms, Hidden Markov Models were constructed and used to annotate observed metagenomic bins. This has allowed us to conclude that the microbial community of the Caspian has adapted to the presence of crude oil and is able to degrade this contaminant through different mechanisms based on oxygen concentration.

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