Methanotroph-derived bacteriohopanepolyol signatures as a function of temperature related growth, survival, cell death and preservation in the geological record.

Interpretation of bacteriohopanepolyol (BHP) biomarkers tracing microbiological processes in modern and ancient sediments relies on understanding environmental controls of production and preservation. BHPs from methanotrophs (35-aminoBHPs) were studied in methane-amended aerobic river-sediment incubations at different temperatures. It was found that: (i) With increasing temperature (4°C-40°C) a 10-fold increase in aminopentol (associated with Crenothrix and Methylobacter spp. growth) occurred with only marginal increases in aminotriol and aminotetrol; (ii) A further increase in temperature (50°C) saw selection for the thermophile Methylocaldum and mixtures of aminopentol and C-3 methylated aminopentol, again, with no increase in aminotriol and aminotetrol. (iii) At 30°C, more aminopentol and an aminopentol isomer and unsaturated aminopentol were produced after methanotroph growth and the onset of substrate starvation/oxygen depletion. (iv) At 50°C, aminopentol and C-3 methylated aminopentol, only accumulated during growth but were clearly resistant to remineralization despite cell death. These results have profound implications for the interpretation of aminoBHP distributions and abundances in modern and past environments. For instance, a temperature regulation of aminopentol production but not aminotetrol or aminotriol is consistent with and, corroborative of, observed aminopentol sensitivity to climate warming recorded in a stratigraphic sequence deposited during the Paleocene-Eocene thermal maximum (PETM).

The Bacteriohopanepolyol Inventory of Novel Aerobic Methane Oxidising Bacteria Reveals New Biomarker Signatures of Aerobic Methanotrophy in Marine Systems.

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.

Analysis of non-derivatised bacteriohopanepolyols by ultrahigh-performance liquid chromatography/tandem mass spectrometry.

RATIONALE: Traditional investigation of bacteriohopanepolyols (BHPs) has relied on derivatisation by acetylation prior to gas chromatography/mass spectrometry (GC/MS) or liquid chromatography/MS (LC/MS) analysis. Here, modern chromatographic techniques (ultrahigh-performance liquid chromatography (UPLC)) and new column chemistries were tested to develop a method for BHP analysis without the need for derivatisation. METHODS: Bacterial culture and sedimentary lipid extracts were analysed using a Waters Acquity Xevo TQ-S triple quadrupole mass spectrometer in positive ion atmospheric pressure chemical ionisation (APCI) mode. Waters BEH C18 and ACE Excel C18 were the central columns evaluated using a binary solvent gradient with 0.1% formic acid in the polar solvent phase in order to optimise performance and selectivity. RESULTS: Non-amine BHPs and adenosylhopane showed similar performance on each C18 column; however, BHP-containing terminal amines were only identified eluting from the ultra-inert ACE Excel C18 column. APCI-MS/MS product ion scans revealed significant differences in fragmentation pathways from previous methods for acetylated compounds. The product ions used for targeted multiple reaction monitoring (MRM) are summarised. CONCLUSIONS: UPLC/MS/MS analysis using an ACE Excel C18 column produced superior separation for amine-containing BHPs and reduced run times from 60 to 9 min compared with previous methods. Unexpected variations in fragmentation pathways between structural subgroups must be taken into account when optimising MRM transitions for future quantitative studies. Copyright © 2016 John Wiley & Sons, Ltd.

A temperate river estuary is a sink for methanotrophs adapted to extremes of pH, temperature and salinity.

River Tyne (UK) estuarine sediments harbour a genetically and functionally diverse community of methane-oxidizing bacteria (methanotrophs), the composition and activity of which were directly influenced by imposed environmental conditions (pH, salinity, temperature) that extended far beyond those found in situ. In aerobic sediment slurries methane oxidation rates were monitored together with the diversity of a functional gene marker for methanotrophs (pmoA). Under near in situ conditions (4-30°C, pH 6-8, 1-15 g l(-1) NaCl), communities were enriched by sequences affiliated with Methylobacter and Methylomonas spp. and specifically a Methylobacter psychrophilus-related species at 4-21°C. More extreme conditions, namely high temperatures ≥ 40°C, high ≥ 9 and low ≤ 5 pH, and high salinities ≥ 35 g l(-1) selected for putative thermophiles (Methylocaldum), acidophiles (Methylosoma) and haloalkaliphiles (Methylomicrobium). The presence of these extreme methanotrophs (unlikely to be part of the active community in situ) indicates passive dispersal from surrounding environments into the estuary.