2006 Volume 1 Issue 4 Pages 165-177
The depth distribution of sulphate-reducing bacteria (SRB) in the water column of a meromictic lake, Lake Suigetsu, Fukui, Japan was investigated using quantitative competitive PCR targeting the gene coding for portions of the α-subunit of dissimilatory sulphite reductase (dsrA). The total bacterial cell density (DAPI count) was 5−13×106 cells mL−1 in the water column of the lake with maximum abundance occurring at the oxic-anoxic interface layer. SRB were not detected in oxic surface water using competitive PCR. SRB were found in the anoxic waters below the oxycline ranging from 104 to 105 cells mL−1, accounting for 0.3–8.9% of the total bacteria. The SRB cell densities were higher than previously estimated using the most-probable-number (MPN) method. Sequencing of the cloned PCR product of dsrA showed the existence of different SRB groups in the anoxic water. The majority of the dsrA sequences were associated with the Desulfosarcina-Desulfococcus-Desulfonema group and members of the Desulfobulbaceae family. Other dsrA clones belonged to the Desulfomicrobium and Desulfovibrio species as well as to a deeply branched group in the dsrA tree with no representatives from previously isolated SRB groups. These SRB species appear to be important for the sulphur and carbon cycle in the anoxic waters of Lake Suigetsu.
