ESTIMATION OF CELL NUMBERS OF METHANOTROPHIC BACTERIA IN BOREAL PEATLANDS BASED ON ANALYSIS OF SPECIFIC PHOSPHOLIPID FATTY-ACIDS

Concentrations of two phospholipid fatty acids (PLFAs) specific for methane-oxidizing bacteria (16:1 omega 8 and 18:1 omega 8), were used to estimate the biomass and cell numbers of this group of bacteria in two Sphagnum-dominated boreal peatlands. Concentration ranges of 16:1 omega 8 and 18.1 omega 8 were 0.0-73 and 1.0-486 pmol g(-1) of wet peat, respectively. Concentrations in the peat of each fatty acid were positively correlated with the potential methane oxidation activity (V-max), which was used as an independent estimate of methanotrophic biomass. This correlation suggests that the two PLFAs are good biomarkers for the population of methanotrophic bacteria in peatlands. Concentrations of the two PLFAs were transformed to cell numbers using conversion factors for the cell content of PLFAs,average cell volume and percentage of cellular dry matter. The total cell number of methanotrophic bacteria in peat samples from a range of sites and depths ranged between 0.3 and 51 x 10(6) cells g(-1) of wet pear, with similar proportions of type I and type II methanotrophic bacteria in most samples. Within particular peat profiles, numbers of methanotrophic bacteria were highest around the level of the water table, implying that the supplies of methane and oxygen largely determine the biomass distribution of methanotrophic bacteria in this type of peatlands.