Reduction of Nitrate in Shewanella oneidensis depends on atypical NAP and NRF systems with NapB as a preferred electron transport protein from CymA to NapA
In the genome of Shewanella oneidensis, a napDAGHB gene cluster encoding periplasmic nitrate reductase (NapA) and accessory proteins and an nrfA gene encoding periplasmic nitrite reductase (NrfA) have been identified. These two systems seem to be atypical because the genome lacks genes encoding cytoplasmic membrane electron transport proteins, NapC for NAP and NrfBCD/NrfH for NRF, respectively. Here, we present evidence that reduction of nitrate to ammonium in S. oneidensis is carried out by these atypical systems in a two-step manner. Transcriptional and mutational analyses suggest that CymA, a cytoplasmic membrane electron transport protein, is likely to be the functional replacement of both NapC and NrfH in S. oneidensis. Surprisingly, a strain devoid of napB encoding the small subunit of nitrate reductase exhibited the maximum cell density sooner than the wild type. Further characterization of this strain showed that nitrite was not detected as a free intermediate in its culture and NapB provides a fitness gain for S. oneidensis to compete for nitrate in the environments. On the basis results from mutational analyses of napA, napB, nrfA and napBnrfA in-frame deletion mutants, we propose that NapB is able to favor nitrate reduction by routing electrons to NapA exclusively.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 963571
- Report Number(s):
- PNNL-SA-66068; KP1501021; TRN: US200918%%394
- Journal Information:
- The ISME Journal, 3(8):966-976, Vol. 3, Issue 8
- Country of Publication:
- United States
- Language:
- English
Similar Records
Functional roles of CymA and NapC in reduction of nitrate and nitrite by Shewanella putrefaciens W3-18-1
Resolution of two native monomeric 90 kDa nitrate reductase active proteins from Shewanella gelidimarina and the sequence of two napA genes