Heterotrophic Nitrification in Thiosphaera-Pantotropha - Oxygen-Uptake and Enzyme Studies

SUMMARY: Thiosphaera pantotropha is a heterotrophic nitrifying bacterium which reduces nitrite produced from ammonia to nitrogen gas, regardless of the ambient dissolved O2 concentration. Under certain growth conditions, nitrous oxide may be produced. The ammonia oxygenase showed a number of similarities with that of autotrophic nitrifiers [e.g. light sensitivity, Mg2+ requirement, NAD(P)H utilization], as did the hydroxylamine oxidoreductase (cytochrome c oxidation, hydrazine inhibition). However, there were also differences (e.g. hydroxylamine inhibition of ammonia oxidation) and this apparent similarity may be superficial. Control experiments with a strain of Paracoccus denitrificans (which does not nitrify) did not show the presence of either enzyme.