Origin and preservation of bacteriohopanepolyol signatures in Sphagnum peat from Bissendorfer Moor (Germany)

Abstract

Distributions of bacteriohopanepolyols (BHPs) were investigated in a peat core from the Bissendorfer Moor (Germany) in order to test the utility of BHPs as indicators of microbial processes in peats. Between 13 and 22 BHPs were identified in each sample (23 structures in total), with total concentrations ranging from 160 – 2800 µg g-1TOC. We have tentatively ascribed sources of most BHPs observed at this site via comparison of known BHPs source organisms with recent microbiological studies on the peat microbiome. Members of the Alpha-, Beta- and Gammaproteobacteria and specifically the genera Burkholderia, Bradyrhizobium and Rhodoblastus, as well as other phyla including the cyanobacteria, Acidobacteria and Acetobacteria are amongst the most likely sources. Additionally, BHP signatures which could be assigned directly to methane oxidising bacteria (35-aminobacteriohopanepentol and 35-aminobacteriohopanepentol) were present only at very low levels, supporting previous studies which have shown that the majority of precursor organisms biosynthesising hopanoids in peat environments are heterotrophs. The surface layers also contained a highly unusual signature comprising high concentrations of unsaturated compounds, including unsaturated bacteriohopanetetrol pseudopentose, which has previously only been reported in Gloeocapsa cyanobacteria. This genus is known to occur in symbiotic association with host Sphagnum species, and has the ability to fix atmospheric nitrogen which is a well known trait amongst members of the peat microbiome and amongst hopanoid producing microorganisms. The apparent capacity for hopanoids to protect organisms from external stresses such as low pH is therefore likely to be a significant factor accounting for the high BHP contributions from heterotrophs, methanotrophs and phototrophic organisms in Sphagnum peats.