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 me thane-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 tw o Sphagnum-dominated boreal peatlands. Concentration ranges of 16:1 om ega 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 posi tively 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. Concentration s of the two PLFAs were transformed to cell numbers using conversion f actors for the cell content of PLFAs,average cell volume and percentag e of cellular dry matter. The total cell number of methanotrophic bact eria 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 pa rticular peat profiles, numbers of methanotrophic bacteria were highes t around the level of the water table, implying that the supplies of m ethane and oxygen largely determine the biomass distribution of methan otrophic bacteria in this type of peatlands.