Methanogens and methanotrophs distribution in the hyporheic sediments of a small lowland stream

Distribution of microbial activity, methanogenic archaea and type I and II methanotrophs were studied in a small lowland stream Sitka in Czech Republic. The methanogens and methanotrophic bacteria were detected using FISH with 16 S rRNA-targeted oligonucleotide probes. The highest microbial density was obtained in the upper sediment layer 0-25 cm; this zone corresponded also to that of the highest metabolic activity, as indicated by the methanogenic potential, methanotrophic activity, INT and FDA profiles. Both methanogenic archaea and aerobic methanotrophs were found at all localities along the longitudinal stream profile. The proportion of these groups to the DAPI-stained cells was quite consistent and varied only slightly but a higher proportion to the DAPI-stained cells in the deeper sediment layer 25-50 cm was observed. On average 23.4 % of DAPI-stained cells were detected by FISH with a probe for methanogens while type I methanotrophs reached similar to 21.4 % and type II methanotrophs 11.9 %, respectively. The percentage of DAPI-stained cells hybridizing with methanotroph-specific probes was generally higher for type I than type II. Our data show that the methanogenic archaea and aerobic methanotrophs can be numerically dominant components of the hyporheic biofilm community and affect CH4 cycling in river sediments.