A composite biochemical system for bacterial nitrate and nitrite assimilation as exemplified by Paracoccus denitrificans

Andrew J Gates , Victor Luque-Almagro , Alan Goddard , Stuart John Ferguson , María Dolores Roldán , David J Richardson (1)

1 School of Biological Sciences

The denitrifying bacterium Paracoccus denitrificans can grow aerobically or anaerobically using nitrate or nitrite as the sole N-sources. The biochemical pathway responsible is expressed from a gene cluster comprising a: nitrate/nitrite transporter (NasA), nitrite transporter (NasH), nitrite reductase (NasB), ferredoxin (NasG) and nitrate reductase (NasC). NasB and NasG are essential for growth with nitrate or nitrite as N-source. NADH serves as electron-donor for nitrate and nitrite reduction, but only NasB has a NADH-oxidising domain. Nitrate and nitrite reductase activities show the same KM for NADH and can be separated by anion-exchange chromatography, but only fractions containing NasB retain the ability to oxidise NADH. This implies that NasG mediates electron-flux from the NADH-oxidising site in NasB to the sites of nitrate and nitrite reduction in NasC and NasB, respectively. Delivery of extracellular nitrate to NasBGC is mediated by NasA, but both NasA and NasH contribute to nitrite uptake. The roles of NasA and NasC can be substituted during anaerobic growth by the biochemically-distinct membrane-bound respiratory nitrate reductase (Nar), demonstrating functional overlap. nasG is highly conserved in nitrate/nitrite assimilation gene clusters, consistent with a key role for the NasG ferredoxin, as part of a phylogenetically widespread composite nitrate and nitrite reductase system.

Keywords: Life Sciences

Andrew J Gates, Victor Luque-Almagro, Alan Goddard, Stuart John Ferguson, María Dolores Roldán, et al.. A composite biochemical system for bacterial nitrate and nitrite assimilation as exemplified by Paracoccus denitrificans. Biochemical Journal, 2011, 435 (3), pp.743-753. ⟨10.1042/BJ20101920⟩. ⟨hal-00586470⟩