This study investigates the diversity, abundance, and composition of Acidobacteria communities in a wide range of soil types using pyrosequencing and clone library analyses. The researchers collected 87 soils from North and South America and analyzed them for Acidobacteria using two methods: pyrosequencing (39,707 sequences) and clone libraries (1,787 sequences). They found that Acidobacteria represented 30.9% of all classified bacterial sequences in the soils, with their abundance strongly correlated with soil pH (R = -0.80, P < 0.001). The study also identified 8,643 unique phylotypes of Acidobacteria, with one phylotype (subgroup 1) being particularly abundant. The relative abundance of Acidobacteria subgroups was significantly correlated with pH, and the community composition was highly predictable based on pH alone. The results suggest that soil pH acts as an effective habitat filter, restricting community membership to narrowly defined lineages as pH deviates from neutrality. The study highlights the importance of considering broad-scale biogeographic surveys to understand the natural history of bacterial lineages that are difficult to culture.This study investigates the diversity, abundance, and composition of Acidobacteria communities in a wide range of soil types using pyrosequencing and clone library analyses. The researchers collected 87 soils from North and South America and analyzed them for Acidobacteria using two methods: pyrosequencing (39,707 sequences) and clone libraries (1,787 sequences). They found that Acidobacteria represented 30.9% of all classified bacterial sequences in the soils, with their abundance strongly correlated with soil pH (R = -0.80, P < 0.001). The study also identified 8,643 unique phylotypes of Acidobacteria, with one phylotype (subgroup 1) being particularly abundant. The relative abundance of Acidobacteria subgroups was significantly correlated with pH, and the community composition was highly predictable based on pH alone. The results suggest that soil pH acts as an effective habitat filter, restricting community membership to narrowly defined lineages as pH deviates from neutrality. The study highlights the importance of considering broad-scale biogeographic surveys to understand the natural history of bacterial lineages that are difficult to culture.