Enhancement of Nitrobacter activity by heterotrophic bacteria

The present work shows that a supply which is not sterile and which contains organic matter does not interfere with the performance of a column filled with a support previously inoculated with Nitrobacter winogradskyi serotype agilis. Measurements of oxidation rates give results higher than those obtained under axenic conditions (maximum oxidation rate: 220 mg NO 2 − h −1 l −1 of reactor volume under non-sterile conditions: 160 mg NO 2 − h −1 l −1 of reactor volume under axenic conditions). This finding has concentrated our work on the effect of heterotrophic bacteria and of organic matter on the growth of Nitrobacter. We show that a fermentation filtrate of a heterotrophic bacterium ( Pseudomonas sp.) added to a fermenter culture of Nitrobacter produces an increase of activity. Experimental results indicate an appreciable reduction in the latence period (15-0 h) and a considerable increase in the rate of growth of Nitrobacter. (Maximum growth rate with 10% of heterotrophic filtrate: 0.044 h −1; without filtrate: 0.032 h −1.)