• Freshwater lake;
  • Sulfate reduction rate;
  • Sulfate-reducing bacterium;
  • Oligonucleotide probe;
  • Population dynamics


Seasonal changes in the population of sulfate-reducing bacteria (SRB) in the profundal sediments of a freshwater lake, Lake Kizaki, Japan, were directly determined using oligonucleotide probes complementary to the 16S ribosomal RNA of the major phylogenetic groups of SRB. The results based on the hybridization indicated that relative 16S rRNA abundance (RNA index) of Bacteria and Gram-negative mesophilic SRB detected by probes EUB 338 and SRB 385 with respect to all known organisms as detected by probe UNIV 1400 in surface sediments (0–6 cm) were 71% and 4.1% on average for 15 months, respectively. The RNA indexes of the major SRB genera to all bacteria in the 0–3-cm and 3–6-cm layers, on average, were 1.4% for Desulfobulbus, 0.6% for Desulfobacterium, and 0.5% for Desulfovibrio. The RNA indexes of Desulfobulbus showed relatively high values in those of detected SRB during almost all of the study periods, while Desulfobacterium and Desulfovibrio exhibited low relative abundance. The RNA index of Desulfobulbus correlated with the rate of sulfate reduction in the sediment. Therefore, Desulfobulbus appears to be dominant in the active SRB population in the surface sediment.