Screening of Denitrifying Bacteria and Determination of the Culture Conditions

The denitrification function of denitrifying bacteria depended on two substances, nitrate reductase and nitrite reductase induced by nitrate and nitrite respectively. The denitrifying process must be under the condition with nooxygen or little oxygen supplied. The intensity of denitrification was determined by the method of Giltay medium, and dilution plate method was used to determine the optimum medium, aerobic characteristic and best growth temperature for screened bacterial strains. Two strains with high denitrification were screened out of 45 denitrifying bacteria. B88 and B237 degraded nitrate and nitrite much better, produced gas earlier and faster than other strains. B88 and B237 were aerobic and the growth was restricted by oxygen supply under no denitrifying process. The increase of CO2 content had stronger inhibition on the growth of both strains. The growth speed of different denitrifying bacteria varied with medium and temperatures. Among the three medium often used for denitrifying bacteria, nitrate medium, denitrifying bacteria medium and YB medium, YB medium was the optimum. The best growing temprature for the two srrains was about 30℃. Each strain had its own highest density in certain medium, on rotary shaker in YB medium, thehighest densities of B88 and B237 were 6.1×108·mL-1 and 1.54×108·mL-1, respectively.