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

Abstract

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).

Fatty Acid and Hopanoid Adaption to Cold in the Methanotroph Methylovulum psychrotolerans

“…The three strains exhibited similar hopanol distributions to each other (see Table 3 for data for the individual strains), although to a lesser degree than with the FAs. Tetra, penta and hexafunctionalised BHPs, from which the hopanols analyzed in this studied are derived, have been described across a range of methanotrophs, including from the genera Methylomarinum , Methylomarinovum , Methylomicrobium , (Rush et al, 2016), Methylomonas , Methylosinus , Methylocella , Methylacidiphilium (van Winden et al, 2012b), Methylobacter (Osborne et al, 2017) as well as in a Methylovulum -like strain M200 (van Winden et al, 2012b). Unsaturated aminotriol and aminotetrol BHPs have only to date been described in a Methylovulum -like strain M200 (van Winden et al, 2012b) which suggests that they are characteristic of the Methylovulum genera.…”

“…β-hydroxy FAs have been detected in a range of methanotrophic bacteria (Bowman et al, 1991) and their source has been identified as the lipid A component of lipopolysaccharides (Wollenweber and Rietschel, 1990), which are a major constituent of the outer membrane of Gram-negative bacteria (Keinänen et al, 2003; Wollenweber and Rietschel, 1990). Methanotrophs also produce bacteriohopanepolyols (BHPs) which can be tetra, penta or hexafunctionalised (Cvejic et al, 2000a; van Winden et al, 2012b; Rush et al, 2016; Osborne et al, 2017). BHPs have been identified with a range of modifications including 3β-methylation and unsaturations at the Δ 6 and Δ 11 positions (Talbot et al, 2007a).…”

“…Changes in hopanoids with changing growth temperature has been reported for non-methanotrophs, such as Frateuria aurantia (Joyeux et al, 2004), Zymomonas mobilis (Hermans et al, 1991) and Bacillus acidocaldarius (Poralla et al, 1984). However, only a limited number of studies have examined the effect of temperature on the lipid composition of methanotrophic bacteria: a study of “CEL 1923” [thought to be Methylomonas methanica ; Jahnke et al (1999)], a mesocosm experiment with Sphagnum moss colonized by symbiotic methanotrophs (van Winden, 2011; van Winden et al, 2012a) and a study of methane-amended aerobic river-sediment incubations (Osborne et al, 2017).…”

Environmental controls on bacteriohopanepolyol profiles of benthic microbial mats from Lake Fryxell, Antarctica

“…It should be noted that the abundance of BHT II produced by any one organism may also vary with environmental conditions. BHPs may be regulated in response to particular environmental conditions, such as temperature (Kulkarni, Wu, & Newman, ; Osborne et al., ), pH (Garby et al., ; Kulkarni et al., ), and nutrient concentrations (Doughty, Hunter, Summons, & Newman, ). It is possible that environmental conditions present in marine OMZ systems may prompt the production of high abundances of BHT II while conditions in Lake Fryxell do not.…”

“…It should be noted that the abundance of BHT II produced by any one organism may also vary with environmental conditions. BHPs Lake Fryxell may be regulated in response to particular environmental conditions, such as temperature (Kulkarni, Wu, & Newman, 2013;Osborne et al, 2017), pH (Garby et al, 2017;Kulkarni et al, 2013), and nutrient concentrations (Doughty, Hunter, Summons, & Newman, 2009).…”