Open AccessInfluence of temperature on pathways to methane production in the permanently cold profundal sediment of Lake Constance
Author(s) -
Schulz Silke,
Conrad Ralf
Publication year - 1996
Publication title -
fems microbiology ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.377
H-Index - 155
eISSN - 1574-6941
pISSN - 0168-6496
DOI - 10.1111/j.1574-6941.1996.tb00299.x
Subject(s) - methanogenesis , propionate , valerate , profundal zone , chloroform , biology , acetogenesis , fluoroacetate , methane , isovalerate , incubation , environmental chemistry , bacteria , biochemistry , sediment , nuclear chemistry , chromatography , chemistry , ecology , butyrate , fermentation , paleontology , genetics
The in situ temperature of the profundal sediment of Lake Constance is constant at 4°C. Methanogenic bacteria could not be detected at 6°C by the most probable number (MPN) technique using acetate and as methanogenic substrates. Instead, homoacetogenic bacteria were detected on . At a higher temperature of 20°C, however, methanogenic bacteria were found in numbers of about 10 5 cells ml −1 with and about 5 × 10 4 cells ml −1 with acetate. However, CH 4 production was observed at both 4°C and 20°C. Production of CH 4 was inhibited by chloroform and fluoroacetate and the accumulation of intermediary metabolites was measured. At the in situ temperature of 4°C, only acetate accumulated in presence of chloroform. Hydrogen partial pressures were at the same low value of about 0.5 Pa as in the uninhibited control. The amount of accumulated acetate was similar to that of CH 4 in the uninhibited controls. Similar results were obtained with fluoroacetate which inhibits methanogenesis from acetate. Addition of H 14 CO 3 − did not result in the formation of 14 CH 4 after 28 days of incubation. However, [2‐ 14 C]acetate was immediately converted to 14 CH 4 . The results indicate that methanogenesis at 4°C was exclusively due to acetate cleavage. At 20°C, by contrast, accumulation of H 2 was observed in addition to that of acetate, propionate, valerate, caproate, methanol and isopropanol, when CH 4 production was inhibited by chloroform. Thermodynamic calculations indicated that the accumulation of the fatty acids was a consequence of feedback inhibition by the accumulated H 2 . Balance calculations indicated that at 20° about 22% of the CH 4 originated from reduction of CO 2 . Experiments with H 14 CO 3 − indicated that about 33% of the CH 4 originated from at 20°C. Thermodynamic calculations showed that homoacetogenesis from was endergonic, whereas methanogenesis from acetate or was exergonic at both 4°C and 20°C. Low sediment temperatures obviously limited methanogenesis from for reasons other than thermodynamics. Simultaneously, degradation processes seemed to be dominated by homoacetogenic degradation of organic matter followed by acetoclastic methanogenesis. However, increase of temperature resulted in a dramatic shift of the degradation pathway enhancing the role of H 2 as an intermediate.