N-210. Composition, Diversity, and Novelty within Soil Proteobacteria
The majority of the soil’s biosphere contains biodiversity that remains yet to be discovered. The occurrence of novel bacterial phyla in soil, as well as the phylogenetic diversity within bacterial phyla with few cultured representatives (e.g. Acidobacteria, Verrucomicrobia, and Gemmatimonadetes) have been previously well documented. However, few studies have focused on the novel phylogenetic diversity within phyla containing numerous cultured representatives. Here, we present a detailed phylogenetic analysis of the Proteobacteria-affiliated clones identified from 13,001 nearly full-length 16S rRNA gene clones derived from Oklahoma tall grass prairie soil. Proteobacteria was the most abundant phylum in the community, and comprised 25% of total clones. The most abundant and diverse class within the Proteobacteria was Alphaproteobacteria, which comprised 41% of Proteobacteria clones, followed by the Deltaproteobacteria, Betaproteobacteria, and Gammaproteobacteria, which made up 38, 13, and 7% of Proteobacteria clones, respectively. Members of the Epsilonproteobacteria were not detected in the dataset. Detailed phylogenetic analysis indicated that 14% of the Proteobacteria clones belonged to seven novel orders and 57% belonged to orders with no described cultivated representatives or were unclassified. Within the Betaproteobacteria, one novel order and 13 novel families were detected. Also, 85% of Betaproteobacteria clones belonged to family-level lineages containing no described or characterized isolates and 69% belonged to orders containing no described representatives, MND1 and A21b. This work provides detailed phylogenetic evidence for novel lineages within the subdivisions of Proteobacteria and we can conclude that although this phylum contains more cultivated microorganisms than any other phylum, the majority of soil Proteobacteria belong to lineages whose members remain uncultivated. Thus, the functions of soil microorganisms belonging to well-described phyla, such as Proteobacteria, are not yet understood.