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

Abstract

The profundal sediment of Lake Constance has a constant temperature of 4°C. Incubation at temperatures increasing in steps of 2–3°C between 2 and 49°C resulted in increasing CH4 production rates that exhibited a shoulder at 25°C with rates of about 3 nmol h−1 ml−1, a maximum at 34°C with rates of about 18 nmol h−1 ml−1, and then declined to low rates again. Production of 14CH4 from [2-14C]acetate occurred at all temperatures. It increased with temperature reaching a maximum at 36–40°C, and then decreased rapidly. Production of 14CH4 from H14CO3−, on the other hand, was only detectable at temperatures higher than 22°C. It then increased rapidly, reached a maximum at 30°C and then decreased again. The absence of H2/CO2-dependent CH4 production at low temperature was probably due to substrate limitation, since addition of H2/CO2 at 4°C increased the percentage of H2/CO2-dependent methanogenesis from undetectable levels to about 100%. Addition of cellulose had only a minor stimulatory effect on the formation of 14CH4 from H14CO3−, indicating that H2 formation from cellulose was limited by the low temperature. The addition of H2/CO2 also resulted in increased incorporation of H14CO3− into acetate, indicating the operation of chemolithotrophic homoacetogenesis. Incubation of sediment at temperatures higher than 35°C resulted in increased production of acetate, lactate, propionate, butyrate, caproate and isopropanol. At 45°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.