Temperature dependence of methane production from different precursors in a profundal sediment (Lake Constance)

The profundal sediment of Lake Constance has a constant temperature of 4 degrees C. Incubation at temperatures increasing in steps of 2-3 degrees C between 2 and 49 degrees C resulted in increasing CH4 production rates that exhibited a shoulder at 25 degrees C with rates of about 3 nmol h(-1) ml(-1), a maximum at 34 degrees C with rates of about 18 nmol h(-1) ml(-1), and then declined to low rates again. Production of (CH4)-C-14 from [2-C-14]acetate occurred at all temperatures. It increased with temperature reaching a maximum at 36-40 degrees C, and then decreased rapidly. Production of (CH4)-C-14 from (HCO3-)-C-14, on the other hand, was only detectable at temperatures higher than 22 degrees C. It then increased rapidly, reached a maximum at 30 degrees C and then decreased again. The absence of H-2/CO2-dependent CH4 production at low temperature was probably due to substrate limitation, since addition of H-2/CO2 at 4 degrees C increased the percentage of H-2/CO2-dependent methanogenesis from undetectable levels to about 100%. Addition of cellulose had only a minor stimulatory effect on the formation of (CH4)-C-14 from (HCO3-)-C-14, indicating that H-2 formation from cellulose was limited by the low temperature. The addition of H-2/CO2 also resulted in increased incorporation of (HCO3-)-C-14 into acetate, indicating the operation of chemolithotrophic homoacetogenesis. Incubation of sediment at temperatures higher than 35 degrees C resulted in increased production of acetate, lactate, propionate, butyrate, caproate and isopropanol. At 45 degrees C production rates reached values of <2 nmol h(-1) ml(-1), except acetate production which reached a rate of about 28 nmol h(-1) ml(-1). Obviously, fermentation of organic matter was enhanced at these temperatures and was not balanced by further degradation of the fermentation products to CH4. Our results demonstrate a tremendous metabolic capacity of the permanently cold profundal sediment at much higher temperatures, but apparently to a different extent for the different physiological groups of anaerobic bacteria.