Polyfunctionalised bio- and geohopanoids in the Eocene Cobham Lignite

Abstract

25We investigated the bacteriohopanepolyol (BHP) distribution in the Cobham Lignite 26 sequence (SE England) deposited across the Palaeocene-Eocene boundary including part 27 of the Palaeocene-Eocene Thermal Maximum (PETM) as shown previously by a negative 28 carbon isotope excursion (CIE). A variety of BHPs were identified, including the commonly 29 occurring and non-source specific biohopanoid bacteriohopanetetrol (BHT) and 32, anhydroBHT which was the most abundant polyfunctionalised geohopanoid in the majority of 31 samples. BHPs with a terminal amine functionality, diagnostic biomarkers for methanotrophic 32 bacteria were identified throughout the sequence, with similar distributions in both the lower 33 laminated and upper blocky lignite except that 35-aminobacteriohopanepentol (aminopentol) 34 indicative of Type I methanotrophs (gammaproteobacteria) was generally more abundant in 35 the upper section within the CIE. 36 37The diagenetic fate of these compounds is currently poorly constrained, however, we also 38 identified the recently reported N-containing transformation product anhydroaminotriol and 39 several tentatively assigned novel N-containing structures potentially containing ketone 40 functionalities. Although present throughout the section, there is a sharp peak in the 41 occurrence of these novel compounds correlated with the onset of the CIE and highly 42 isotopically depleted hopanes in the upper part of the laminated lignite, both also correlate 43 well with peak abundance of aminopentol. The significant abundance of these compounds 44 suggests that 35-amino BHPs have their own specific diagenetic pathway, potentially 45 providing an alternative method allowing methanotroph activity to be traced in older samples 46 even if the original biohopanoid markers are no longer present. 47At this time we cannot preclude the possibility that some or all of these BHPs have been 48produced by more recent subsurface activity, post deposition of the lignite to date; however, 49 that would not be expected to generate the observed stratigraphic variability and we suggest 50 that unprecedented observations of a range of highly functionalised biohopanoids in 51 samples of this age could significantly extend the window of their known occurrence. 52

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

“…We can therefore discount SRB as the source of aminopentol in an environmental sample with a high ratio of aminopentol:aminotriol. A similar approach was recently used by [49] based on the ratio of aminotetrol:aminotriol which has been found in the range 1:20–100 in some species of Desulfovibrio SRB [47,50,51]. Interestingly, some of the species of SRB cultures analysed by Blumenberg et al [47,50,51] also synthesised diplopterol and diploptene, which could explain the enhanced presence of these lipids in CH 4 -influenced anoxic sites.…”

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

“…) . Another possibility is a structure related to the novel side‐chain methylated compounds recently identified in extracts from the Eocene Cobham Lignite . Although the exact position of the side‐chain methylation could not be determined in that study, it was proposed that it is most likely to be located at C31 by comparison with other studies .…”

“…Bacteriohopanetetrol (BHT; Ia ) is the most commonly occurring of all known BHP structures and has been reported widely in bacterial cultures and modern, recent and ancient samples up to 56 Ma . The acetylated BHT protonated molecule ([M + H] + = m/z 715) is unstable under APCI conditions, resulting in rapid loss of one functional group and a base peak ion of m/z 655 ([M + H–CH 3 COOH] + ).…”

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

“…S2c) but within a more physically, chemically and biologically complex sediment setting. However, additional contributions from other microorganisms within the sediment cannot be ruled out as aminotriol has a diverse range of biological sources (Neunlist and Rohmer, , Talbot et al ., ; van Winden et al ., ). Aminotetrol ( II ) was also significantly enriched at 4°C–30°C albeit at lower absolute concentrations (Fig.…”

“…AminoBHPs are found in soils, wetlands, lakes, river, estuarine and marine sediments across different climate regions (Talbot et al ., and references therein). Aminotetrol, aminopentol and C‐3 methylated aminoBHPs in particular, are of interest in distinguishing type I and II methanotrophs and, critically, are used to identify sites of intense aerobic methane oxidation and the dispersal of materials from such locations.…”