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

Distributions of bacteriohopanepolyols (BHPs) in a peat core from the Bissendorfer Moor (Germany) were investigated in order to test the utility of BHPs as indicators of microbial processes in peats. Between 13 and 22 BHPs in each sample (23 structures in total) were identified, with total concentration ranging from 160–2800μg/gTOC. We have tentatively ascribed sources of most BHPs at the site via comparison of known BHP source organisms with recent microbiological studies of 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 among the most likely sources. Additionally, BHP signatures which could be assigned directly to methane oxidising bacteria (35-aminobacteriohopanepentol and 35-aminobacteriohopanetetrol) were present only at very low level, 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 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 N2, which is a well known trait among members of the peat microbiome and among 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.