Composition and temporal dynamics of planktonic archaeal assemblages from anaerobic sulfurous environments studied by 16S rDNA denaturing gradient gel electrophoresis and sequencing

The planktonic archaeal assemblages of several anaerobic, sulfide-rich, aqu atic environments were analyzed in space and time by PCR-denaturing gradien t gel electrophoresis and sequencing of 16S rRNA gene fragments. The system s were sampled in different years between 1992 and 1998. PCR products were obtained directly from the original DNA without previous nested amplificati on and yielded successful fingerprints with mostly sharp bands in the gel. Nineteen samples from the anaerobic hypolimnia of 8 lakes and 1 coastal lag oon in NE Spain, Mallorca and Switzerland were compared and a temporal surv ey was carried out in one of the lakes (Lake Vilar). Between 4 and 14 well- defined bands appeared. All the sequenced bands belonged to Archaea. Althou gh most of the water bodies shared the same climatic conditions and presenc e of sulfide, the limnological parameters were different among them and dif ferent finger-prints were observed in different lakes. Euryarchaeota, i.e., methanogen- and thermoplasma-related sequences, appeared in all the sample s but crenarchaeota were recovered only from Lake Vilar. A temporal shift i n the predominant members of the archaeal assemblage from crenarchaeota to members of the cluster of thermoplasmales and relatives took place in Lake Vilar between February and June. Sequences related to thermoplasmales and c renarchaeota were distantly related to cultured strains (81 % similarity in 16S rDNA) and clustered with branches represented only by environmental cl ones, whereas sequences related to methanogens grouped with a sequence from an endosymbiont of 1 anaerobic ciliate. A new branch of freshwater euryarc haeota appeared within the cluster of thermoplasmales and relatives. Our st udy indicates the presence of dynamic archaeal populations in the water col umn of nonthermophilic, sulfide-rich environments, further extending the di versity and distribution of Archaea in nature. The temporal shift in commun ity composition in Lake Vilar suggests that Archaea grow under in situ cond itions. If this is the case, Archaea would be active players in the anaerob ic biogeochemical cycles of these environments.