Lipids of symbiotic methane-oxidizing bacteria in peat moss studied using stable carbon isotopic labelling

Aerobic symbiotic methane-oxidizing bacteria (methanotrophs) in peat moss (Sphagnum spp) play a vital role in the carbon cycle in peat bogs They reduce methane emissions and provide CO2 to Sphagnum moss, resulting in effective in situ carbon recycling To establish biomarkers for these methanotrophs, sphagnum moss spp were incubated with (CH4)-C-13 and analysed for the degree of label incorporation in individual lipids We determined that mono-unsaturated fatty acids (FAs, C16 1 omega 7 and C18 1 omega 7), hopenes [hop-17(21)-ene and 2-methylhop-17(21)-ene] and tetrafunctionalized hopanoids (detected as 17 beta,21 beta-bishomohopanol after H5IO6 and NaBH4 treatment) are probably the prevailing methanotroph lipids in Sphagnum moss spp However, they are not unique for methanotrophs, as they have been detected in other ;bacteria. Natural delta C-13 values of these lipids in Sphagnum range from -31 parts per thousand to -38 parts per thousand Their limited isotopic depletion is probably the result of a mixed origin On the other hand, an origin from senile cycle methanotrophs (type II) that fix both CO2 and CH4 and are, therefore, isotopically less depleted, would also be consistent with the observed isotopic values We have not been able to identify an unambiguous biomarker for methanotrophs in peat moss. Nevertheless, our results show that a limited depletion in C-13 for hopanoids does not exclude the presence of an active methanotrophic community. (C) 2010 Elsevier Ltd All rights reserved