The significance of early accumulation of nanomolar concentrations of NO as an inducer of denitrification

Abstract

Denitrifying bacteria have variable ability to perform efficient and balanced denitrification during oxygen depletion. NO is often assumed to exert a positive feedback in the transcription of denitrification genes, because NO-dependent activators have been identified. The regulatory network of denitrification is complex, however, and the significance of NO signalling needs to be studied in vivo. We utilized acetylene-catalysed NO oxidation to scavenge NO produced by batch cultures of denitrifying bacteria during transition from oxic to anoxic respiration, to explore the effects on the kinetics of NO, N2O and N2 production. The results demonstrated that nanomolar concentrations of NO accumulating prior to complete depletion of oxygen exert a significant positive feedback on the initiation of denitrification in Paracoccus denitrificans. The early NO signal appeared essential to minimize the transient accumulation of NO during the subsequent anoxic phase for Agrobacterium tumefaciens, but not for P. denitrificans and Pseudomonas aureofaciens. In summary, the results indicate that the early accumulation of nanomolar concentrations of NO has a significant, but strain-dependent effect on the expression of denitrification. © 2012 Federation of European Microbiological Societies.