Enumeration of Heterotrophic Bacteria in River Waters by Using a Low Nutrient Medium

Abstract

Enumeration of heterotrophic bacteria in river waters of differing degree of eutrophica-tion has been done by using agar media containing different concentrations of organic nutrients. The higger counts of bacteria in any station at any season were obtained by low nutrient agar medium (0.5g of polypeptone, 0.25g of yeast extract, 0.1g of glucose, and 15g of agar in 1, 000ml of distilled water), in comparison with the counts of bacteria on high nutrient media. It was suggested from these results that the low nutrient medium is superior to recover the heterotrophic bacteria inhabiting in river waters. Furthermore, it has been found that bacteria isolated from less polluted waters were more sensitive to high nutrient concentrations than those from highly polluted waters in experiments on the growth response of bacteria to the concentrations of organic nutrients.
Since the higher counts of bacteria in river waters were obtained at about 35°C in summer and about 20°C in winter, it appears that incubation temperature for counting must be selected in accordance with water temperature in river.