Microflora and bacterial organic acid production in the bottom sediment of Lake Biwa.

Abstract

The microflora of the bottom sediments in the mesotrophic Northern Lake and the eutrophic Southern Lake were investigated. The organic content in the sediment was higher in the Southern Lake than in the Northern Lake, whereas the redox potential and the concentrations of total sulfides and organic acids indicated that the sediment in the Northern Lake is under more reduced condition than that in the Southern Lake. In the sediment of the Northern Lake, the facultative anaerobes Aeromonas and Vibrio were predominant, whereas the obligate aerobe Micrococcus was predominant in the Southern Lake. Clostridum was predominant among the obligate anaerobes in both the Northern and Southern Lakes, but the generic composition of the anaerobes did not greatly differ between the two Lakes. The number and activity of organic acid producers were larger in the Northern Lake than in the Southern Lake. Many bacteria isolated from the sediment produced acetate, formate, butyrate, propionate, lactate and citrate. In these organic acids, acetate was produced by numerous bac-teria. Organic acids were produced by facultative anaerobes rather than by obligate anaerobes. The activity of organic acid production by facultative anaerobes in the Northern Lake did not decrease even at lower temperature. Based on these results, it is considered that the facultative anaerobes capable of producing organic acids play a significant role in the accumulation of organic acids in the sediment of the Northern Lake.