ASSESSING IN SITU DEGRADATION OF PETROLEUM HYDROCARBONS BY INDIGENOUS MICROBIAL COMMUNITIES

Abstract

<p>Biodegradation of petroleum hydrocarbons by microorganisms is one of the most effective methods used to remediate environmental systems. However, much of what is known is based on the ability of (mostly bacterial) species to degrade hydrocarbons under enrichment conditions in a laboratory setting. In order to refine biodegradation as a remediation method, there is a critical need to understand the dynamics and mechanisms of microbial communities under <em>in situ </em>conditions. The goal of this dissertation was to provide insight and knowledge into the function of microbial communities in petroleum-contaminated environments using a combination of DNA, lipid and isotopic analyses. Microbial biomass, community structure, carbon sources were assessed at two study sites: (1) a former industrial facility contaminated by PAHs and (2) coastal salt marshes impacted by the <em>Deepwater Horizon</em> oil spill.</p> <p>Isotopic analyses of soils collected from the PAH-contaminated site revealed that microbial carbon sources were derived from vegetation and/or natural organic matter present in soils matter rather than PAHs. Similarly, microbial community structure remained consistent across samples and there were no observed shifts in phylotype diversity with increasing levels of PAHs. Bioaccessibility assays revealed that a large fraction of soil-borne PAHs at the site are not bioavailable to microorganisms; thus, highlighting the importance of environmental factors to <em>in situ</em> biodegradation.</p> <p>Biodegradation of <em>Deepwater Horizon </em>spilled oil was detected in salt marsh sediments such that petroleum-derived carbon was a primary carbon source for indigenous microbial communities in the months following the spill. Likewise, pyrosequencing of all three microbial domains showed an increase in the relative of abundance of taxonomic groups known to include hydrocarbon-degrading species, such as <em>Sphingomonadales</em>. These results suggest that Gulf of Mexico marsh sediments have considerable biodegradation potential and that natural attenuation may be feasible remediation strategy in this region.</p>