Thiosphaera pantotropha, a facultative anaerobe is capable of mixotrophic and heterotrophic growth on a wide range of substrates. It can oxidize reduced sulfur compounds, nitrify ammonia heterotrophically to nitrite, and reduce nitrate or nitrite to nitrogen gas irrespective of the ambient dissolved oxygen concentration.(1) The ammonia oxygenase has similarities with that of autotrophic nitrifiers (such as, light sensitivity, Mg2+ requirement, and NAD(P)H utilization), so has hydroxylamine oxidoreductase (cytochrome C oxidation, hydrazine inhibition) but there are some differences too (e.g., hydroxylamine inhibition of ammonia oxidation).(2) It is the denitrifying enzyme system expression and operation under aerobic conditions, however, which is shrouded with controversy. The typical enzyme system of the bacterium throws open interesting possibilities of its applications for wastewater treatment. T. pantotropha has been tested in mixed bacterial cultures in suspended as well as fixed film systems to treat simulated industrial and domestic wastewaters. It has also been used in a flocculating algal-bacterial system to treat synthetic fertilizer wastewater. Fixed film systems have yielded better results. High rates of simultaneous removal of organics and nitrogen have been achieved. This indicates a vast improvement over conventional treatment strategies.