Identifier

etd-04142014-105341

Degree

Master of Science (MS)

Department

Environmental Sciences

Document Type

Thesis

Abstract

The effects of the Deepwater Horizon (DWH) oil spill on the bacterial communities in coastal sediments are relatively known but few studies have been published evaluating the impacts of the spill on oil-degrading bacterial populations in the salt marsh sediments of Barataria Bay, Louisiana. The aims of this study were to determine the effects of the oil spill on the microbial community in Barataria Bay, Louisiana through the determination of predominate species of oil-degrading bacteria in marsh sediments, and to determine how well certain bacterial isolates can degrade crude oil in the region by taking samples from three areas of different oiling categories in April 2012, October 2012 and April 2013, approximately 24, 30, and 36 months after the initial oiling event. Hydrocarbon-degrading bacteria were isolated from the sediment samples using Bushnell Haas (BH) agar enriched with 1% Light Louisiana Sweet (LLS) crude oil. The isolates were subsequently purified on LB agar plates, their genomic DNAs extracted, and 16S rRNA genes amplified by polymerase chain reaction (PCR). The PCR products of 16S rRNA were then sequenced and taxonomically classified based on similarity to known sequences in BLAST database. A total of 460 isolates were obtained, representing 84 species from 45 genera in 6 phyla. Oil degradability of 10 bacterial isolates, designated to Staphylococcus xylosus, Acinetobacter calcoaetious, Pseudomonas stutzeri, Bacillus pumilus, Micrococcus luteus, Rhodococcus equi, Microbacterium esteratomaticum, Vibrio sp., Pseudomonas mendocina, and Agromyces aurantiacus, respectively, was tested in LB broth with 1% LLS crude oil. Their growth and metabolic properties in terms of optical density at 600 nm and pH in culture medium were monitored for 6 days. Among these isolates, Micrococcus luteus, Vibrio sp., Bacillus pumilus, Rhodococcus equi and Microbacterium esteratomaticum appeared to have the greatest ability to degrade LLS crude oil; their growth rates were estimated to be 0.038, 0.037, 0.031, 0.029 and 0.037 per hour, respectively. All isolates showed a decrease in pH in their culture medium during their growth, with M. esteratomaticum having the lowest pH of 5.29 and R. equi having the highest pH of 6.50 at 96 hours of incubation. A decrease in pH in the cultured media is indicative of an accumulation of acid from oxidation reactions carried out by oil-degrading bacteria. The present study provided a comprehensive list of indigenous oil-degrading bacteria in Louisiana marsh sediment, which is critical in developing bioremediation strategies.

Date

2014

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Hou, Aixin

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