Nitrification and denitrification by Thiosphaera pantotropha in aerobic chemostat cultures

Abstract

Tlliosyhaeru panrotrophn has been reported to denitrify aerobically and nitrify heterotrophically. Hokever. recent evidence has indicated that these properties (particularly aerobic denitrification) have been lost. The occurrence and levels of aerobic denitrification and heterotrophic nitrification by 7'. parztntrophu in chemostat cultures have therefore been re-evaluated. Only low nitrate reduction rates were observed: the apparent nitrogen loss was of the same order of magnitude as the combined error in the calculated nitrogen consumption. However, '"N mass spectrometry revealed low aerobic denitrification rates (about 10% of the rates originally published by this group). Heterotrophic nitrification rates were about a third of previous observations. N2 and N,O were both produced from NH:, NO; and NO;. Periplasmic nitrate reductase was present in aerobically grown cells.