PhD Defense by Will A. Overholt

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  • Date/Time:
    • Wednesday March 14, 2018 - Thursday March 15, 2018
      1:00 pm - 2:59 pm
  • Location: Engineered Biosystems Building, Children's Healthcare of Atlanta Seminar Room (EBB 1005)
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Summary Sentence: The response of marine benthic microbial populations to the Deepwater Horizon oil spill

Full Summary: No summary paragraph submitted.


In partial fulfillment of the requirements for the degree of 


Doctor of Philosophy in Bioinformatics

in the 

School of Biological Sciences


Will A. Overholt


defends his thesis 


The response of marine benthic microbial populations to the Deepwater Horizon oil spill


Wednesday, March 14, 2018

1:00 pm

Engineered Biosystems Building, Children's Healthcare of Atlanta Seminar Room (EBB 1005)


Thesis Advisor:

Dr. Joel E. Kostka

School of Biological Sciences

Georgia Institute of Technology


Committee Members:

Dr. Markus Huettel

Department of Earth Ocean and Atmospheric Sciences

Florida State University


Dr. Kostas Konstantinidis

School of Civil and Environmental Engineering

Georgia Institute of Technology


Dr. Brian K. Hammer

School of Biological Sciences

Georgia Institute of Technology


Dr. David J. Hollander

College of Marine Sciences

University of South Florida


Dr. Stefan J. Green

Department of Biology and Director of DNA Services

University of Illinois at Chicago


The Deepwater Horizon (DWH) oil spill was the largest accidental oil spill in history, the first large spill that occurred in the deepsea, and is unique in the unparalleled volumes of chemical dispersant that were applied during emergency response efforts. Microbial biodegradation ultimately removes most of the hydrocarbons discharged during oil spills, which allows the system to recover. However, the environmental controls that regulate this process are poorly understood. Furthermore, benthic environments are understudied relative to their pelagic counterparts, and were contaminated with approximately 20 % of the released oil after the DWH disaster. Aside from the emergence of hydrocarbon-degrading bacterial populations, oil contamination may impact sensitive, benthic microbial groups and disrupt critical biogeochemical cycles, causing far-reaching and largely unknown ecosystem level consequences.


The work presented in this dissertation addresses knowledge gaps associated with the environmental controls of the structure and function of benthic microbial communities across the Gulf of Mexico as well as their response to major perturbations such as oil contamination. Specifically, the overall goal was to advance our understanding of the fate and consequences of deposited DWH crude oil to benthic ecosystems and the in situmicrobial community. Objectives were to: (1) determine the impact of chemical dispersant on individual oil-degrading microbial populations and the consequences to oil ecotoxicity, (2) interrogate the natural or baseline state of benthic microbial communities throughout oligotrophic sediments in Gulf of Mexico, and (3) quantify the controls on biodegradation and microbial populations in sandy coastal ecosystems. The results improve our mechanistic understanding of the constraints on the rates and pathways of oil biodegradation. Moreover, the most significant findings from this study demonstrate the occurrence of large-scale disruptions to the marine nitrogen cycle in subtidal sands in response to oil contamination through the inhibition of nitrification. This disruption can be linked to the microbial populations that mediate nitrification along with other nitrogen cycling processes, offering direction for environmental monitoring programs to assess ecosystem health and recovery. The results from this dissertation can be directly incorporated into predictive models to forecast recovery pathways for future spills as well as hindcast the fate of remaining DWH oil.

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Phd Defense
  • Created By: Tatianna Richardson
  • Workflow Status: Published
  • Created On: Mar 1, 2018 - 8:38pm
  • Last Updated: Mar 1, 2018 - 8:38pm