Abstract
Crude oil-amended microcosms were prepared with inocula from eleven anoxic environments (4 river sediments, 3 lake sediments, and 4 sludges from wastewater treatment reactors) to determine their ability to produce methane from the biodegradation of crude oil. Over incubation periods of up to 1150 days, oil-stimulated methanogenesis and concomitant loss of alkanes occurred in microcosms prepared with five of the inocula whereas six of the inocula did not show oil-stimulated methane production. Bacterial and archaeal communities from microcosms exhibiting high levels of oil-stimulated methanogenesis were distinct from communities where methanogenic crude oil degradation was not detected. Successional changes were consistent with the quantitative enrichment of syntrophic hydrocarbon degrading bacteria and methanogens over time. In conclusion, in oil-impacted environments methanogenic crude oil-degrading microbial consortia are present in relatively low abundance and exhibit slow growth, and while they may be ubiquitously distributed they may not be present at sufficiently high abundance to be detected.
Highlights
Microcosms inoculated with sediment or sludge from the other 6 of 11 inocula (Grangemouth, Humberside, and Poland sludge, Priest Pot and Buttermere lake sediments, River Coquet sediment) did not show oil-stimulated methane production relative to the corre sponding no-oil control microcosms (Fig. 1; Table S1)
Total organic carbon (TOC) levels in the River Tees sediment were similar to the Tyne and Wear rriver sediments investigated (TOC (%) Tees 5.58 ± 0.22; Tyne 7.63 ± 0.03; Wear 4.31 ± 0.27; Coquet 1.37 ± 0.03)
To a lesser extent, River Wear sediments may reflect their industrial heritage; both rivers run through cities that were at the heart of the industrial revolution and their sediments have been exposed to hydrocarbon pollution from coal and oil for over 100 years
Summary
It is well documented that n-alkanes, a major fraction of most crude oils, are biodegradable under methanogenic conditions when provided as single, pure compounds (Anderson and Lovely, 2000; Zengler et al, 1999) and in crude oil and other complex mixtures (Berdugo-Clavijo and Gieg., 2014; Clothier and Gieg, 2016; Gieg et al, 2008, 2010; Gray et al, 2010, 2011; Jones et al, 2008; Li et al, 2012; Liang et al, 2015; Mba dinga et al, 2011; Sherry et al, 2010, 2014; Siddique et al, 2006, 2011; Townsend et al, 2003; Zhou et al, 2012). The onset of methanogenic alkane degradation is often preceded by an extended lag phase which has been shown to last hundreds of days for methanogenic degradation of hydrocarbons in mature oil sands tailings (Siddique et al, 2011), in hydrocarbon-amended estuarine sediments (Jones et al, 2008; Sherry et al, 2014) and in anaerobic digesters treating hydrocarbon-contaminated wastewater and soil (Scherr et al, 2012). The long lag periods observed result from slow growth (doubling times >30 days) of populations of the pri mary hydrocarbon degrading bacteria which are present in inocula at very low abundance (Gray et al, 2011)
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