Abstract
Aerobic methane oxidation (AMO) is one of the primary biologic pathways regulating the amount of methane (CH4) released into the environment. AMO acts as a sink of CH4, converting it into carbon dioxide before it reaches the atmosphere. It is of interest for (paleo)climate and carbon cycling studies to identify lipid biomarkers that can be used to trace AMO events, especially at times when the role of methane in the carbon cycle was more pronounced than today. AMO bacteria are known to synthesise bacteriohopanepolyol (BHP) lipids. Preliminary evidence pointed towards 35-aminobacteriohopane-30,31,32,33,34-pentol (aminopentol) being a characteristic biomarker for Type I methanotrophs. Here, the BHP compositions were examined for species of the recently described novel Type I methanotroph bacterial genera Methylomarinum and Methylomarinovum, as well as for a novel species of a Type I Methylomicrobium. Aminopentol was the most abundant BHP only in Methylomarinovum caldicuralii, while Methylomicrobium did not produce aminopentol at all. In addition to the expected regular aminotriol and aminotetrol BHPs, novel structures tentatively identified as methylcarbamate lipids related to C-35 amino-BHPs (MC-BHPs) were found to be synthesised in significant amounts by some AMO cultures. Subsequently, sediments and authigenic carbonates from methane-influenced marine environments were analysed. Most samples also did not contain significant amounts of aminopentol, indicating that aminopentol is not a useful biomarker for marine aerobic methanotophic bacteria. However, the BHP composition of the marine samples do point toward the novel MC-BHPs components being potential new biomarkers for AMO.
Highlights
Methane (CH4) is a potent greenhouse gas, and its atmospheric concentration has tripled since pre-industrial times (e.g. [1,2])
It is of interest forclimate and carbon cycling studies to identify lipid biomarkers that can be used to trace Aerobic methane oxidation (AMO) events, especially at times when the role of methane in the carbon cycle was more pronounced than today
In this study we investigated the BHP distributions in species of three AMO marine genera, and of eight marine environments, six of which were CH4-influenced
Summary
Methane (CH4) is a potent greenhouse gas, and its atmospheric concentration has tripled since pre-industrial times (e.g. [1,2]). Global oceans hold large subsurface reservoirs of CH4 in the form of gas hydrates. These stores are precariously dependent on temperature and pressure. A rapid destabilisation of gas hydrates has been proposed to have caused vast releases of marine CH4 in the past [3]. Pelagic AMO activity rose significantly after the Macondo oil well blowout in 2010 [15]. This activity was short-lived, highlighting the complexity of natural community interactions in response to increased CH4 [16]. It is important to recognise and trace methanotrophy during past extreme events in order to understand its potential to mitigate future CH4 release
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