Microflora and Mineralization Activity in the Bottom Sediment of Lake Biwa

抄録

Microflora and mineralization activity in the bottom sediment taken from two distinct sites in Lake Biwa were investigated.From the colony formation process, the following three common features for soil bacteria were also confirmed in the sediment bacteria:1)the number of colonies increased not continuously but intermittently with incubation time;2)the number of colonies formed on diluted nutrient agar medium was considerably higher than that on nutrient agar;3)the total number of bacteria counted by epifluorescence microscopy was 100 to 10000 times higher than the number of colonies formed on both media.The following features were also found for sediment bacteria:1)the deeper the layer of the sediment, the smaller the number of colonies;2)the southern basin sediments yielded more colonies than northern basin sediments;3)the number of bacteria that can form colonies increased from spring to summer in the sediment sample contrary to the smaller count of total bacteria in the summer sample.From the bacterial activity of glucose mineralization the following points were revealed:1)the upper layer of the sediments are richer in aerobes than facultative anaerobes;and 2)under oxygen-deficient conditions even the upper layer of the sediments becomes rich in facultative anaerobes.As revealed in this study, the combination of observing the colony-forming process on agar medium and the measuring the glucose-mineralizing activity of the bacteria in the sediments seems to be useful for understanding the complex microflora in the sediments and changes relating to various factors, such as, nutrient and oxygen concentration, and temperature.