Assimilation of glucose-derived carbon into methanogenic archaea in soil under unflooded condition

Ecology of methanogenic archaea, one of the obligate anaerobes, in soil under unflooded condition has not been well documented. To elucidate whether methanogenic archaea assimilate carbon derived from easily decomposable organic matters in soil even under unflooded condition, we analyzed bacterial and methanogenic archaeal communities in a soil incubated with 0.5% 12C- and 13C-glucose under upland condition (60% of maximum water holding capacity) by DNA-stable isotope probing (DNA-SIP) and denaturing gradient gel electrophoresis (DGGE). The added glucose was rapidly decomposed within 7 days of the incubation and the bacterial community immediately responded to the added glucose. Clone analysis of the 13C-enriched bacterial 16S rRNA genes (16S rDNA) on the days 2 and 7 showed that not only aerobic and facultative anaerobic bacteria closely related to Bacillus spp., Ammoniphilus spp. (or Oxalophagus spp.), Paenibacillus spp. and Azotobacter spp. but also obligate anaerobes such as Clostridium spp. and Anaerobacter spp. assimilated glucose-derived carbon. By contrast, DGGE band patterns of methanogenic archaeal 16S rDNA obtained from the incubated soil did not change during the incubation period. However, when DGGE band patterns were compared between the 12C- and 13C-glucose treatments after fractionation by isopycnic centrifugation, some DGGE bands were observed from the heavy DNA fractions in the 13C-glucose treatment on the days 7 and 14. The sequences of these DGGE bands were closely related to Methanocella spp., Methanosaeta spp., Methanosarcina spp., the ZC-I group in Methanosarcinales and Methanobacterium spp. The present study showed that a part of glucose-derived C flows to methanogenic archaea in the soil during the glucose decomposition even under unflooded condition.

► Ecology of methanogenic archaea in soil under unflooded condition. ► Soil incubation with 0.5% 12C- and 13C-glucose under upland condition. ► DNA-stable isotope probing and denaturing gradient gel electrophoresis analyses. ► Glucose-derived C assimilation into methanogenic archaea under upland soil condition.