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

AJ Gates, VM Luque‑Almagro, AD Goddard, SJ Ferguson, MD Roldán, DJ Richardson

Research output: Contribution to journalArticle

45 Citations (Scopus)

Abstract

The denitrifying bacterium Paracoccus denitrificans can grow aerobically or anaerobically using nitrate or nitrite as the sole nitrogen source. 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 the nitrogen source. NADH serves as the electron donor for nitrate and nitrite reduction, but only NasB has a NADH-oxidizing 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 oxidize NADH. This implies that NasG mediates electron flux from the NADH-oxidizing 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, which is consistent with a key role for the NasG ferredoxin, as part of a phylogenetically widespread composite nitrate and nitrite reductase system.
Original languageEnglish
Pages (from-to)743-753
Number of pages11
JournalBiochemical Journal
Volume435
Issue number3
DOIs
Publication statusPublished - 24 Feb 2011

Cite this