Effect of temperature change on the composition of the bacterial and archaeal community potentially involved in the turnover of acetate and propionate in methanogenic rice field soil

The microbial community structure was investigated together with the path of methane production in Italian rice field soil incubated at moderate (35 degrees C) and high (45 degrees C) temperature using terminal restriction fragment length polymorphism and stable isotope fractionation. The structure of both the archaeal and bacterial communities differed at 35 degrees C compared with 45 degrees C, and acetoclastic and hydrogenotrophic methanogenesis dominated, respectively. Changing the incubation of the 45 degrees C soil to different temperatures (25, 30, 35, 40, 45, 50 degrees C) resulted in a dynamic change of both microbial community structure and stable isotope fractionation. In all treatments, acetate first accumulated and then decreased. Propionate was also transiently produced and consumed. It is noteworthy that acetate was also consumed at thermophilic conditions, although archaeal community composition and stable isotope fractionation indicated that acetoclastic methanogenesis did not operate. Instead, acetate must have been consumed by syntrophic acetate oxidizers. The transient accumulation and subsequent consumption of acetate at thermophilic conditions was specifically paralleled by terminal restriction fragments characteristic for clostridial cluster I, whereas those of clostridial clusters I and III, Acidaminococcaceae and Heliobacteraceae, paralleled the thermophilic turnover of both acetate and propionate.