Effect of the incubation temperature on the isolation of aerobic heterotrophic bacteria from a river.

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Samples of the water and sediment were collected at midstream and downstream sites of the Tama River from January to December 1983, and incubated aerobically at 5, 10, 20, 30 and 37°C after plating onto 1/20 PYBGF and PYBGF agar plates. As a result, the maximum colony counts were obtained at 20°C of incubation temperature, and Gram-negative, achromogenic bacteria predominated in almost all samples throughout the year, irrespective of the incubation temperatures. However, suspected psychrophiles and mesophiles were isolated at the low incubation temperatures in the colder season and the higher temperatures in the warmer season, respectively. These results suggested that the samples from freshwater environments in the summer and winter seasons, should be incubated at 20°C, and the ambient temperature samples if the more diverse microflora including either psychrophiles or mesophiles is needed to be isolated.