Candidate Division BD: Phylogeny, Distribution and Abundance in Soil Ecosystems

Oligonucleotide primers were designed and used to amplify partial 16S rDNA sequences of the recently identified bacterial group BD from four diverse soils. Phylogenetic analysis of 34 BD group sequences supports division-level status for the group and also indicates that the BD group consists of at least 3 subdivision-level groups. Sequence divergence (21%) amongst these BD group sequences was found to be near the average for bacterial division-level lineages. An intercalating dye-based quantitative PCR (qPCR) assay was used to quantify BD phylogenetic group 3 16S rDNA in Wyoming shortgrass steppe soils. Although BD phylogenetic group 3 16S rDNA sequence numbers were high, averaging 3 × 10 8 copies per g soil, no significant correlations were found between their abundance and soil organic matter content, inorganic N concentration, or pH. Based on microscopically estimated cell numbers and the range of rRNA operons per genome in the bacterial domain, we estimate that BD group 3 represents between 0.75% and 10.7% of the microbial population in a shortgrass steppe soil. Our results indicate that the BD group is widely distributed in the environment and present in significant numbers in Wyoming shortgrass steppe soils.