Phylogenetic diversity of bacteria in the leachate of a full-scale recirculating landfill

We analyzed the phylogenetic composition of bacterial community in the effluent leachate of a full-scale recirculating landfill using a culture-independent molecular approach. 16S rRNA genes were amplified directly from leachate DNA with universally conserved and Bacteria-specific rDNA primers and cloned. The clone library was screened by restriction fragment length polymorphism, and representative rDNA sequences were determined. Many bacterial sequences displaying relatively low levels of similarity to any other hitherto reported rDNA sequences were retrieved. A total of 103 bacterial sequence types were found in 195 analyzed clones. Roughly 90% of the sequence types were affiliated with low-G + C gram-positive bacteria, the Chlamydiae/Verrucomicrobia group and with the Cytophaga-Flexibacter-Bacteroides group, where the clone distribution was 53%, 21% and 19%, respectively. The other 10 sequence types represented 7% of the total clones, and they were either affiliated with well-recognized bacterial divisions Planctomycetes, Spirochaetes, Proteobacteria and Actinobacteria, or grouped within two recently proposed candidate divisions OP9 and OP11. The most frequent sequence type represented less than 10% of the total bacterial 16S rRNA gene sequences, and the 15 more frequent sequence types accounted for at least 47% of these sequences. Some rRNA gene sequences clustered with genera or taxa that were classically identified within anaerobic treatment systems. These results indicate that, despite recent expansion, our knowledge on the microbial diversity in anaerobic treatment systems is still limited.