Abstract
Although methanogenic degradation of hydrocarbons has become a well-known process, little is known about which crude oil tend to be degraded at different temperatures and how the microbial community is responded. In this study, we assessed the methanogenic crude oil degradation capacity of oily sludge microbes enriched from the Shengli oilfield under mesophilic and thermophilic conditions. The microbial communities were investigated by terminal restriction fragment length polymorphism (T-RFLP) analysis of 16S rRNA genes combined with cloning and sequencing. Enrichment incubation demonstrated the microbial oxidation of crude oil coupled to methane production at 35 and 55°C, which generated 3.7±0.3 and 2.8±0.3 mmol of methane per gram oil, respectively. Gas chromatography-mass spectrometry (GC-MS) analysis revealed that crude oil n-alkanes were obviously degraded, and high molecular weight n-alkanes were preferentially removed over relatively shorter-chain n-alkanes. Phylogenetic analysis revealed the concurrence of acetoclastic Methanosaeta and hydrogenotrophic methanogens but different methanogenic community structures under the two temperature conditions. Candidate divisions of JS1 and WWE 1, Proteobacteria (mainly consisting of Syntrophaceae, Desulfobacteraceae and Syntrophorhabdus) and Firmicutes (mainly consisting of Desulfotomaculum) were supposed to be involved with n-alkane degradation in the mesophilic conditions. By contrast, the different bacterial phylotypes affiliated with Caldisericales, “Shengli Cluster” and Synergistetes dominated the thermophilic consortium, which was most likely to be associated with thermophilic crude oil degradation. This study revealed that the oily sludge in Shengli oilfield harbors diverse uncultured microbes with great potential in methanogenic crude oil degradation over a wide temperature range, which extend our previous understanding of methanogenic degradation of crude oil alkanes.
Highlights
Crude oil is a complex mixture containing many thousands of different hydrocarbon compounds, which can be divided into four classes
The percentage of saturated hydrocarbons decreased from 33.4% to 8.660.9% at day 453 in the mesophilic consortium, and to 10.860.7% after 303 days of incubation in the thermophilic consortium (Table 1)
Oily sludge microbes collected from the Shengli oilfield possessed the ability to degrade crude oil n-alkanes and generate methane at both mesophilic (35uC) and thermophilic (55uC) temperatures
Summary
Crude oil is a complex mixture containing many thousands of different hydrocarbon compounds, which can be divided into four classes (saturated hydrocarbons, aromatic hydrocarbons, asphaltene and non-hydrocarbons). The biodegradation of crude oil by natural populations of microorganisms was reported over a century ago. Over the past two decades, it has consistently been shown that crude oil hydrocarbons could be degraded under nitrate-reducing [3], ferric ironreducing [4], sulfate-reducing [5,6] and methanogenic conditions [7,8,9]. Multiple research teams have reported that the entire nalkane fraction of crude oil can be consumed under sulfate reducing and/or methanogenic conditions [6,9,10,11,12,13].
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