The impact of an oil spill on microbial communities (and their bioremediation potential); a Niger Delta case study

Abstract

Crude oil pollution constitutes a serious threat to the environment globally, partly due to the release of toxic substances such as hydrocarbons and heavy metals that are known to greatly impact ecosystems and potentially cause serious health implications. The Niger Delta's ecosystem (Nigeria), for instance, has suffered from a series of severe oil spills for several decades, with serious consequences including biodiversity loss. However, the level of impact on its soil microbial community structure as well as the potential for bioremediation remains unclear. In the present study, a recent oil spill near the Ukepliede community (spring 2018) was analysed to assess the impact this spill had on the soil microbial community/diversity present. The potential for crude oil degradation under aerobic/anaerobic conditions and the impact on the microbial composition/diversity was also assessed through a series of microcosm experiments. This included the assessment of the impact of the addition of (i) different terminal electron acceptors (TEAs) in anaerobic microcosms and (ii) biochar and Tween 80 for the aerobic microcosms. Analyses of the soil from the contaminated area revealed that the contamination still was present six months after the oil spill along with elevated concentration of specific (oil derived) metals such as Cr and Ni, across the whole contaminated area. The highest oil contamination was found at the surface decreasing with depth, but contamination was still found up to one metre depth. A significant shift in the microbial community composition and structure was observed caused by the oil contamination, accompanied by decreasing amount of operational taxonomic unit (OTUs) and diversity across depth. However, an increase in the amount of 16SrRNA gene copy numbers in the contaminated area indicated the proliferation of oil-tolerant microorganisms, with Gamma-, Delta-, Alpha- proteobacteria and Acidobacteriia being dominant across the contaminated area, while Ktedonobacteria dominated the non-contaminated control soils. The detection of PAH-RHD genes in the contaminated area highlighted a clear relationship between the oil contamination and potential in situ hydrocarbon metabolism. Moreover, correlation analysis indicated a significant positive relationship between the oil contaminants (organics, Cr and Ni), the presence of the PAH-RHDGN gene, and the low amounts of OTUs. Parallel microcosm experiments using soils collected from the site indicated substantial oil degradation potential by the soil microbial community under both aerobic and anaerobic conditions, with highest removal efficiencies observed in the aerobic and the anaerobic microcosms when sulfate or Fe(III) were used as TEAs. This was accompanied by a release of significant amounts of Fe and Al in solution under reducing conditions. The presence of oil appeared to drive significant biogeochemical shifts in the microcosms, with substantial reduction of sulfate, nitrate, and Fe(III) when used as TEAs in the anaerobic microcosms. Similarly enhanced oil degradation was observed under aerobic conditions when the microcosms were amended with biochar and Tween 80, with minimal impact on the release of metals in solution, but the removal efficiencies of different oil-derived moieties varied. A lower degradation of the aromatics in the biochar amended microcosms was likely caused by adsorption to the biochar surface thereby reducing microbial access, while a lower removal efficiency of the hydrocarbon moieties in the Tween 80 amended microcosms is most likely linked to an inhibited microbial growth caused by the relative high amount of Tween 80 used. The microbial community structures were generally impacted by the oil contamination, however, known oil-degrading microbes such as Gamma-, Delta-, Alpha- proteobacteria, Acidobacteriia, Melainabacteria, spirochaetia, Plancomycetacia, Acidimicrobiia, Babeliae, and Thermoleophilia were enriched across all microcosms, particul

Date of Award	31 Dec 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Jonathan Lloyd (Supervisor) & Bart Van Dongen (Supervisor)