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).