Anaerobic benzene mineralization by natural microbial communities from Niger Delta

Samuel C Eziuzor,Matthias Schmidt,Carsten Vogt

doi:10.1007/s10532-020-09922-x

Samuel C Eziuzor, Matthias Schmidt + Show 1 more

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https://doi.org/10.1007/s10532-020-09922-x

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Journal: Biodegradation	Publication Date: Dec 2, 2020
Citations: 5	License type: open-access

Affiliation: Helmholtz Centre for Environmental Research

Abstract

The Niger Delta is one of the most damaged ecosystems in the world, mainly due to petroleum contamination by oil exploration accidents. We investigated the natural attenuation potential of Niger Delta subsurface sediment samples for anaerobic hydrocarbon degradation using benzene as a model compound under iron-reducing, sulfate-reducing, and methanogenic conditions. Benzene was slowly mineralized under methanogenic and iron-reducing conditions using nitrilotriacetic acid (NTA)-Fe(III), or poorly crystalline Fe(III) oxyhydroxides as electron acceptors, analyzed by measurement of 13CO2 produced from added 13C-labelled benzene. Highest mineralization rates were observed in microcosms amended with Fe(III) oxyhydroxides. The microbial communities of benzene-mineralizing enrichment cultures were characterized by next-generation sequencing of the genes coding for 16S rRNA and methyl coenzyme M reductase A (mcrA). Abundant phylotypes were affiliated to Betaproteobacteriales, Ignavibacteriales, Desulfuromonadales, and Methanosarcinales of the genera Methanosarcina and Methanothrix, illustrating that the enriched benzene-mineralizing communities were diverse and may contain more than a single benzene degrader. The diversity of the microbial communities was furthermore confirmed by scanning helium-ion microscopy which revealed the presence of various rod-shaped as well as filamentous microbial morphotypes.

Highlights

The Niger Delta is one of the world’s most important wetland and coastal marine ecosystem consisting of rain forest, mangroves and fresh water swamps
It was repeatedly observed that the compound is not degraded under various anoxic conditions in distinct sediments samples, raising the question whether degradation was too slow to be detected by analyzing benzene removal or whether benzene degraders were absent
The results demonstrated a natural attenuation potential of the investigated subsurface sediments for anaerobic hydrocarbon degradation especially under iron-reducing conditions, using benzene as model compound

Summary

Introduction

The Niger Delta is one of the world’s most important wetland and coastal marine ecosystem consisting of rain forest, mangroves and fresh water swamps. Natural attenuation of these compounds may support remediation of the contaminated land; the potential of the indigenous microbial community to degrade oil compounds at anoxic conditions has not been determined yet in the Niger Delta area. Whereas sulfate is the principal electron acceptor for anaerobic hydrocarbon degradation in marine sediments due to its high concentration in seawater (& 28 mM), ferric iron (Fe(III)) is thought to be the counterpart at terrestrial sites due to the ubiquitous presence of iron in terrestrial sediments (Ehrlich 1996). In contrast to soluble electron acceptors for anaerobic respiration like sulfate or nitrate, iron is insoluble at most environmental conditions and forms with OH or O several oxides, e.g., Fe(III) oxyhydroxides (goethite, ferrihydrite) or mixed-valent iron minerals (magnetite) (Usman et al 2018). Besides sulfate and Fe(III), carbonate is a relevant electron acceptor for hydrocarbon degradation, resulting in syntrophic consortia of fermenters and methanogens (Jimenez et al 2016)

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