METHANOGENESIS IN SEDIMENTS FROM DEEP LAKES AT DIFFERENT TEMPERATURES(12-70-DEGREES-C)

Methanogenic degradation of organic matter occurs in a wide temperatur e range from psychrophilic to extreme thermophilic conditions. Mesophi lic and thermophilic methanogenesis is relatively well investigated, b ut little is known about low temperature methanogenesis and psychrophi lic methanogenic communities. The aim of the present work was to study methanogenesis in a wide range of temperatures with samples from sedi ments of deep lakes. These sediments may be considered deposits of dif ferent types of microorganisms, which are constantly exposed to low te mperatures. The main question was how psychrophilic methanogenic micro bial communities compare to mesophilic and thermophilic ones. Methanog enesis in a temperature range of 2-70 degrees C was investigated using sediment samples from Baldegger lake (65 m) and Soppen lake (25 m), S witzerland. Methane production from organic matter of sediments occurr ed at all temperatures tested. An exponential dependence of methane pr oduction rate was found between 2 and 30 degrees C. Methanogenesis occ urred even at 70 degrees C. At the same time stable methane production from organic matter of sediments was observed at temperatures below 1 0 degrees C. Methanogenic microbial communities were enriched at diffe rent temperatures. The communities enriched at 4-8 degrees C had the h ighest activity at low temperatures indicating that a specific psychro philic community exists. Addition of substrates such as cellulose, vol atile fatty acids (butyrate, propionate, acetate), methanol and H-2/CO 2 stimulated methane production at all temperatures. H-2/CO2 as well a s methanol were directly converted to methane under thermophilic condi tions. At low temperatures these substrates were converted to methane by a two-step process. First acetate was formed, followed by methane p roduction from acetate. When acetate concentrations were high, acetocl astic methanogenesis was inhibited at low temperatures. This reaction appears to be one of the ''bottle neck'' in psychrophilic methanogenes is. (C) 1997 IAWQ. Published by Elsevier Science Ltd.