Influence of Corn Steep Liquor on the Oxidation of Ammonia to Nitrite by Nitrosomonas europaea

SUMMARY: The oxidation of ammonia by Nitrosomonas europaea is accelerated in mineral liquid media by the addition of small amounts of com steep liquor or its ‘ash’. The amount of nitrite produced in such cultures usually exceeds the controls by 6–7 times after 6 days. However, in the following days nitrite-production becomes slower and after 14 days the controls have reached the same nitrite concentration as the com steep liquor cultures. Concomitant with the accelerated nitrite-production hydrogen-ion concentration in the cultures increases considerably and may attain values as low as pH 6·3 after 14 days, as compared with c. 7·8 in the controls. The effect of com steep liquor stimulation is more pronounced the smaller the inoculum used. Microscopical examination of slides immersed in cultures during incubation shows that N. europaea adheres to the glass surface only in cultures without com steep liquor. The stimulatory factor in solutions of the ‘ash’ of com steep liquor was not removed by dialysis nor by treatment with cation exchange resins. When the solutions were centrifiiged both washed sediment and supernatant fluid were active. A possible explanation of the com steep liquor effect is that colloidal matter in the solutions absorbs ammonia or any other nutrient in the medium in a way more favourable for their utilization by the organism.