A chemical method for estimating methanogenic biomass

Methane-forming bacteria belong to the archaebacterial kingdom and as such possess unique membrane lipids in that phytanyl ether linked phospholipids replace the more usual ester linked analogues. A common methanogenic membrane ether lipid (Di-Phytanyl Glycerol Ether; DPGE) can be extracted using solvents, chemically broken down, derivatized, purified using thin layer chromatography, and finally analysed quantitatively by capillary gas chromatography. In order to evaluate the concentration of DPGE as a means of estimating the biomass of methanogens, this membrane lipid was compared with cell numbers, methane production and turbidity at 578 nm in a controlled growth experiment of a marine methanogenic monoculture of Methanolobus tindarius. It was found that the DPGE lipid data produced similar growth curves to the other measured parameters. All the parameters used to monitor the growth experiment showed an interesting change at a point in the growth cycle of M. tindarius where cell division slowed down and the growth of individual cells appeared to be the major mechanism of increasing the biomass. Preliminary environmental samples taken from both a marine inter-tidal and a freshwater site were analysed for the DPGE lipid and the results are discussed.