Ammonium assimilation by the nitrate-utilizing yeast, Candida nitratophila
C R Hipkin1, K J Flynn1, E Marjot1
1Biochemistry Research Group, School of Biological Sciences, University College of Swansea, Singleton Park, Swansea, SA2 8PP, UK.
The New Phytologist
|April 20, 2021
Summary
Candida nitratophila rapidly assimilates ammonium using glutamate dehydrogenase and glutamine synthetase pathways. The glutamine synthetase/glutamate synthase pathway is predominant in nitrogen-deficient yeast cells.
Area of Science:
- Microbiology
- Biochemistry
- Yeast Metabolism
Background:
- Nitrate-utilizing yeast, Candida nitratophila, assimilates nitrogen sources for growth.
- Understanding nitrogen assimilation pathways is crucial for microbial physiology.
Purpose of the Study:
- To investigate the mechanisms of ammonium assimilation in Candida nitratophila.
- To determine the roles of glutamate dehydrogenase and glutamine synthetase/glutamate synthase pathways.
Main Methods:
- Enzyme activity assays (glutamate dehydrogenase, glutamine synthetase, glutamate synthase).
- In vitro enzyme inhibition studies using azaserine and methionine sulphoximine.
- In vivo ammonium assimilation experiments.
Main Results:
- Nitrogen-replete Candida nitratophila showed high NADPH-dependent glutamate dehydrogenase and glutamine synthetase activity.
- Enzyme activities were derepressed under nitrogen-limiting conditions or when transferred to nitrate medium.
- Nitrogen-deficient cells exhibited NADH-dependent glutamate synthase activity, inhibited by azaserine.
- In vivo ammonium assimilation was inhibited by methionine sulphoximine, and azaserine caused glutamine accumulation.
Conclusions:
- Candida nitratophila possesses both glutamate dehydrogenase and glutamine synthetase/glutamate synthase pathways for ammonium assimilation.
- The glutamine synthetase/glutamate synthase pathway appears to be the predominant route in nitrogen-deficient cells.
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