Mechanism of biological denitrification inhibition: procyanidins induce an allosteric transition of the membrane-bound nitrate reductase through membrane alteration

• Published in: FEMS microbiology ecology 2016-05, Vol.92 (5), p.fiw034-fiw034
• Main Authors: Bardon, Clément, Poly, Franck, Piola, Florence, Pancton, Muriel, Comte, Gilles, Meiffren, Guillaume, Haichar, Feth el Zahar
• Format: Article
• Language: English
• Subjects: Allosteric enzymes; Allosteric Regulation; Biflavonoids; Biodiversity and Ecology; Catechin; Cell Membrane - metabolism; Cell Membrane - ultrastructure; Chemical properties; Denitrification; Environmental Sciences; Fallopia - metabolism; Fallopia - microbiology; Membranes (Biology); Nitrate Reductase - chemistry; Nitrate Reductase - metabolism; Nitrates; Nitrates - metabolism; Oxidation-Reduction; Oxidoreductases - genetics; Physiological aspects; Prevention; Proanthocyanidins - metabolism; Pseudomonas - enzymology; Pseudomonas - metabolism; Pseudomonas - ultrastructure
• ISSN: 1574-6941; 0168-6496; 1574-6941
• DOI: 10.1093/femsec/fiw034

Recently, it has been shown that procyanidins from Fallopia spp. inhibit bacterial denitrification, a phenomenon called biological denitrification inhibition (BDI). However, the mechanisms involved in such a process remain unknown. Here, we investigate the mechanisms of BDI involving procyanidins, using the model strain Pseudomonas brassicacearum NFM 421. The aerobic and anaerobic (denitrification) respiration, cell permeability and cell viability of P. brassicacearum were determined as a function of procyanidin concentration. The effect of procyanidins on the bacterial membrane was observed using transmission electronic microscopy. Bacterial growth, denitrification, NO3- and NO2-reductase activity, and the expression of subunits of NO3- (encoded by the gene narG) and NO2-reductase (encoded by the gene nirS) under NO3 or NO2 were measured with and without procyanidins. Procyanidins inhibited the denitrification process without affecting aerobic respiration at low concentrations. Procyanidins also disturbed cell membranes without affecting cell viability. They specifically inhibited NO3- but not NO2-reductase. Pseudomonas brassicacearum responded to procyanidins by over-expression of the membrane-bound NO3-reductase subunit (encoded by the gene narG). Our results suggest that procyanidins can specifically inhibit membrane-bound NO3-reductase inducing enzymatic conformational changes through membrane disturbance and that P. brassicacearum responds by over-expressing membrane-bound NO3-reductase. Our results lead the way to a better understanding of BDI. Procyanidins, the first identified biological denitrification inhibitors, inhibit membrane-bound nitrate reductase activity through a conformational change related to membrane alteration. Graphical Abstract Figure. Procyanidins, the first identified biological denitrification inhibitors, inhibit membrane-bound nitrate reductase activity through a conformational change related to membrane alteration.