The phylum Acidobacteria is currently represented mostly by environmental 16S rRNA gene sequences, and the phylum so far contains only four species with validly published names, Holophaga foetida, Geothrix fermentans, Acidobacterium capsulatum and Terriglobus roseus. In the present study, two novel strains of acidobacteria were isolated. High-throughput enrichments were set up with the MicroDrop technique using an alpine calcareous soil sample and a mixture of polymeric carbon compounds supplemented with signal compounds. This approach yielded a novel, previously unknown acidobacterium, strain Jbg-1T. The second strain, Wbg-1T, was recovered from a co-culture with a methanotrophic bacterium established from calcareous forest soil. Both strains represent members of subdivision 1 of the phylum Acidobacteria and are closely related to each other (98.0 % 16S rRNA gene sequence similarity). At a sequence similarity of 93.8–94.7 %, strains Jbg-1T and Wbg-1T are only distantly related to the closest described relative, Terriglobus roseus KBS 63T, and accordingly are described as members of the novel genus Edaphobacter gen. nov. Based on the DNA–DNA relatedness between strains Jbg-1T and Wbg-1T of 11.5–13.6 % and their chemotaxonomic and phenotypic characteristics, the two strains are assigned to two separate species, Edaphobacter modestus sp. nov. (the type species), with strain Jbg-1T (=ATCC BAA-1329T =DSM 18101T) as the type strain, and Edaphobacter aggregans sp. nov., with strain Wbg-1T (=ATCC BAA-1497T =DSM 19364T) as the type strain. The two novel species are adapted to low carbon concentrations and to neutral to slightly acidic conditions.

Four stratified basins in Lake Kivu (Rwanda-Democratic Republic of the Congo) were sampled in March 2007 to investigate the abundance, distribution, and potential biogeochemical role of planktonic archaea. We used fluorescence in situ hybridization with catalyzed-reported deposition microscopic counts (CARD-FISH), denaturing gradient gel electrophoresis (DGGE) fingerprinting, and quantitative PCR (qPCR) of signature genes for ammonia-oxidizing archaea (16S rRNA for marine Crenarchaeota group 1.1a [MCG1] and ammonia monooxygenase subunit A [ amoA ]). Abundance of archaea ranged from 1 to 4.5% of total DAPI (4′,6-diamidino-2-phenylindole) counts with maximal concentrations at the oxic-anoxic transition zone (∼50-m depth). Phylogenetic analysis of the archaeal planktonic community revealed a higher level of richness of crenarchaeal 16S rRNA gene sequences (21 of the 28 operational taxonomic units [OTUs] identified [75%]) over euryarchaeotal ones (7 OTUs). Sequences affiliated with the kingdom Euryarchaeota were mainly recovered from the anoxic water compartment and mostly grouped into methanogenic lineages ( Methanosarcinales and Methanocellales ). In turn, crenarchaeal phylotypes were recovered throughout the sampled epipelagic waters (0- to 100-m depth), with clear phylogenetic segregation along the transition from oxic to anoxic water masses. Thus, whereas in the anoxic hypolimnion crenarchaeotal OTUs were mainly assigned to the miscellaneous crenarchaeotic group, the OTUs from the oxic-anoxic transition and above belonged to Crenarchaeota groups 1.1a and 1.1b, two lineages containing most of the ammonia-oxidizing representatives known so far. The concomitant vertical distribution of both nitrite and nitrate maxima and the copy numbers of both MCG1 16S rRNA and amoA genes suggest the potential implication of Crenarchaeota in nitrification processes occurring in the epilimnetic waters of the lake.