Molecular ecology of a facultative swine waste lagoon

To investigate the microbial ecology of three facultative swine waste lagoons. Phylogenetic analysis of sequences in a 16S rRNA gene clone library and fluorescence in situ hybridization (FISH) analyses were used to assess bacterial diversity in a swine waste lagoon. FISH analysis and Gram-staining were used to compare the microbial communities of all three swine waste lagoons. Six operational taxonomic units were in high relative abundance and corresponded to the following phylotypes; Thiolamprovum, Verrucomicrobia, Acholeplasma, Turicibacter, Clostridium and Bacteroides. PCR was employed to detect the genes apsA and dsrAB which encode for enzymes specifically associated with dissimilatory sulfate-reduction within sulfate-reducing bacteria (SRB). Amplification of these genes confirmed their presence within the lagoons. All lagoons were dominated by purple sulfur bacteria, affiliated to Thiolamprovum pedioforme. The molecular identification of fermentative bacteria and SRB indicate the following metabolic processes within such facultative ponds: sulfur-cycling, fermentation, inter-species hydrogen transfer and carbon cycling. This study provides the first molecular evidence for the existence of a sulfur cycle which is linked to phototrophic sulfide oxidation by purple bacteria and organotrophic sulfate-reduction by SRB.