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DNRA for nitrogen assimilation or energy conservation in Bacillus azotoformans LMG 9581T

Yi-hua Sun (UGent) , Paul De Vos (UGent) and Kim Heylen (UGent)
Author
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Abstract
Bacteria can contain the gene inventory for both denitrification and dissimilatory nitrate reduction to ammonium (DNRA), previously thought to be mutually exclusive processes. Detailed studies of these microorganisms could shed light on the differentiating environmental drivers of both processes without interference of organism-specific variation. Bacillus azotoformans shows a remarkable redundancy of dissimilatory nitrogen reduction, with multiple copies of each denitrification gene as well as nrfAH, but has reduced capacity for nitrogen assimilation, with no nas operon nor amtB gene. We hypothesized that (i) ammonium could not be used as sole nitrogen source, and (ii) DNRA, if expressed, would solely conserve energy and not lead to nitrogen assimilation during anaerobic growth. Batch experiments were conducted with various C/N ratios, and different concentrations of nitrate, nitrite, ammonium and yeast extract. Growth could be supported by ammonium as sole nitrogen source but required yeast extract added to the medium. Nevertheless, ammonium had a clear effect on growth rate, while yeast extract concentration determined growth yield. No ammonium was produced via DNRA in nitrogen limiting conditions, but limited ammonium amounts were consumed (±0.3 mM). Comparable to Shewanella loihica, we generally observed a denitrification phenotype for all growth conditions tested, with all supplied nitrate converted to nitrous oxide (acetylene inhibition method). Only when using nitrite as sole electron acceptor or in combination with nitrate, ammonium production was observed, but the nitrogen masses were not balanced. These observations need to be explored further. In conclusion, the Firmicute B. azotoformans requires organic nitrogen for assimilation and does not use DNRA to compensate for the lack of a nas operon in nitrogen limiting conditions. If and when functional, DNRA will thus contribute to energy conservation, but the determining environmental conditions need to be resolved using continuous culturing experiment and compared to those for the Gammaproteobacterial S. loihica.

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MLA
Sun, Yi-hua, Paul De Vos, and Kim Heylen. “DNRA for Nitrogen Assimilation or Energy Conservation in Bacillus Azotoformans LMG 9581T.” Nitrogen Cycle, 20th European Meeting, Abstracts. 2015. Print.
APA
Sun, Yi-hua, De Vos, P., & Heylen, K. (2015). DNRA for nitrogen assimilation or energy conservation in Bacillus azotoformans LMG 9581T. Nitrogen Cycle, 20th European meeting, Abstracts. Presented at the 20th European Nitrogen Cycle meeting.
Chicago author-date
Sun, Yi-hua, Paul De Vos, and Kim Heylen. 2015. “DNRA for Nitrogen Assimilation or Energy Conservation in Bacillus Azotoformans LMG 9581T.” In Nitrogen Cycle, 20th European Meeting, Abstracts.
Chicago author-date (all authors)
Sun, Yi-hua, Paul De Vos, and Kim Heylen. 2015. “DNRA for Nitrogen Assimilation or Energy Conservation in Bacillus Azotoformans LMG 9581T.” In Nitrogen Cycle, 20th European Meeting, Abstracts.
Vancouver
1.
Sun Y, De Vos P, Heylen K. DNRA for nitrogen assimilation or energy conservation in Bacillus azotoformans LMG 9581T. Nitrogen Cycle, 20th European meeting, Abstracts. 2015.
IEEE
[1]
Y. Sun, P. De Vos, and K. Heylen, “DNRA for nitrogen assimilation or energy conservation in Bacillus azotoformans LMG 9581T,” in Nitrogen Cycle, 20th European meeting, Abstracts, Aberdeen, Scotland, UK, 2015.
@inproceedings{8508003,
  abstract     = {Bacteria can contain the gene inventory for both denitrification and dissimilatory nitrate reduction to ammonium (DNRA), previously thought to be mutually exclusive processes. Detailed studies of these microorganisms could shed light on the differentiating environmental drivers of both processes without interference of organism-specific variation. Bacillus azotoformans shows a remarkable redundancy of dissimilatory nitrogen reduction, with multiple copies of each denitrification gene as well as  nrfAH, but has reduced capacity for nitrogen assimilation, with no nas operon nor amtB gene. We hypothesized that (i) ammonium could not be used as sole nitrogen source, and (ii) DNRA, if expressed, would solely conserve energy and not lead to nitrogen assimilation during anaerobic growth.
Batch experiments were conducted with various C/N ratios, and different concentrations of nitrate, nitrite,  ammonium and yeast extract. Growth could be supported by ammonium as sole nitrogen source but required yeast extract added to the medium. Nevertheless, ammonium had a clear effect on growth rate, while yeast extract concentration determined growth yield. No ammonium was produced via DNRA in nitrogen limiting conditions, but limited ammonium amounts were consumed (±0.3 mM).  Comparable to Shewanella loihica, we generally observed a denitrification phenotype for all growth conditions tested, with all supplied nitrate converted to nitrous oxide (acetylene inhibition method). Only when using nitrite as sole electron acceptor or in combination with nitrate, ammonium production was observed, but the nitrogen masses were not balanced. These observations need to be explored further. 
In conclusion, the Firmicute B. azotoformans requires organic nitrogen for assimilation and does not use DNRA to compensate for the lack of a nas operon in nitrogen limiting conditions. If and when functional, DNRA will thus contribute to energy conservation, but the determining environmental conditions need to be resolved using continuous culturing experiment and compared to those for the Gammaproteobacterial S. loihica.},
  author       = {Sun, Yi-hua and De Vos, Paul and Heylen, Kim},
  booktitle    = {Nitrogen Cycle, 20th European meeting, Abstracts},
  language     = {eng},
  location     = {Aberdeen, Scotland, UK},
  title        = {DNRA for nitrogen assimilation or energy conservation in Bacillus azotoformans LMG 9581T},
  year         = {2015},
}