Studies in gas production by bacteria

Abstract

O denitrifying bacillus isolated from sea water and Cranston''s apparatus were used for measuring the rate of N production by denitrifying bacteria cultivated in a broth medium containing nitrate or nitrite. Denitrification curves so obtained showed 9 stages, with a general similarity to a bacterial growth curve. Reduction of nitrate is shown to occur in stages; O is evolved at each stage and utilized for respiration, but N is produced only at the last stage, when it is liberated as gaseous waste metabolite. The following factors affecting duration of initial lag phase, were studied quantitatively: (i) time of addition of nitrite or nitrate [long dash]It is found that under the experimental conditions the lag is made up of a normal bacterial lag of 81/2 hrs., and a "chemical lag" of 41/2 hrs. before gas production, this chemical lag being due to the time necessary for formation of intermediate compounds. (ii) Concentration of nitrite or nitrate[long dash]In a series of similar cultures with 6, 12, 18, 24 and 30 mg. KNO3 added, the lag phase was prolonged to 11, 13, 18, 37 and 49 hrs., respectively. The initial concentration of nitrate is thus an extremely important factor. (iii) Initial pH of medium[long dash]4 nitrite broth cultures with initial pH values of 8.2, 8.0, 6.8 and 6.4, showed with increased acidity a progressive increase in lag periods to 14, 18, 51 and 400 hrs., respectively. (iv) Incubation temp.[long dash]In a series of cultures incubated at 18, 25, 30, 35 and 40[degree]C., lag periods were found to be 26, 20, 17, 13 and 25 hrs., respectively.