Construction and Preliminary Analysis of the 16S rDNA Clone Library of Bacteria in the Xifeng Loess Section, the Northwest of China

The development of culture-independent techniques using nucleic acids has provided much new insight into studies of microbial diversity of soils. In this study, the bulk DNA was extracted and purified from the loess deposit in the Xifeng Section, the northwest of China, and subjected to PCR amplification with primers specific for 16S rRNA gene sequences (rDNAs). Then a 16S rDNA clone library was constructed and 44 clones were sequenced. Phylogenetic analysis of these sequences revealed extensive diversity. Guided by the phylogenetic tree, bacteria fell into 13 main lineages: Proteobacteria, Acidobacteria, Actinobacteria, Chloroflexi, Firmicutes, Verrucomicrobia, Planctomycetes, Gemmatimonadetes, Deinococcus-Thermus, Nitrospirae, Cyanobacteria, Bacteroidetes and Candidate division TG1. It is striking to find that the Acidobacteria division was the most abundant phylogenetic group in loess, occupying 43.3% of total clones. Acidobacteria group includes 17 gene types and 65 clones, most of which are uncultured type. The Proteobacteria division (26.7%) was the second-predominant bacterial community, including 13 gene types and 40 clones. These two divisions (accounting for 70% of clones) represented the majority of the identified phylotypes in loess. However, further study is needed to probe into the function and environmental implications for the two predominant bacterial communities in loess.