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Mapping Bacterial Functional Networks and Pathways in Escherichia Coli using Synthetic Genetic Arrays
Published on: November 12, 2012
Apparent genetic redundancy facilitates ecological plasticity for nitrate transport
S E Unkles1, D Zhou, M Y Siddiqi
1School of Biology, University of St Andrews, St Andrews KY16 9TH, UK.
The EMBO Journal
|November 15, 2001
Summary
Aspergillus nidulans uses two nitrate transporters, NrtA and NrtB, for efficient nitrogen uptake. Their coordinated regulation and distinct kinetics enable growth across variable nitrate concentrations.
Area of Science:
- Molecular Biology
- Mycology
- Biochemistry
Background:
- Aspergillus nidulans utilizes nitrate as a primary nitrogen source.
- High-affinity nitrate transporters are crucial for nitrogen assimilation in fungi.
- Understanding nitrate transporter function is key to fungal growth and metabolism.
Purpose of the Study:
- To investigate the roles of two high-affinity nitrate transporters, NrtA and NrtB, in Aspergillus nidulans.
- To characterize the kinetic properties and regulation of NrtA and NrtB.
- To elucidate the mechanisms of nitrate acquisition in response to varying environmental concentrations.
Main Methods:
- Construction and analysis of nrtA and nrtB single and double mutants.
- Growth assays on different nitrate concentrations.
- 13NO3(-) flux analysis to determine transporter kinetics (Km and Vmax).
Main Results:
- Single mutants (nrtA or nrtB) grew normally on 1-10 mM nitrate.
- The double mutant (nrtA nrtB) failed to grow on nitrate concentrations up to 200 mM.
- NrtA exhibited a Km of ~100 µM and Vmax of ~600 nmol/mg/h, while NrtB showed a Km of ~10 µM and Vmax of ~100 nmol/mg/h.
- NrtA and NrtB genes were coordinately regulated under various conditions.
Conclusions:
- NrtA and NrtB play essential, distinct roles in high-affinity nitrate uptake in Aspergillus nidulans.
- Kinetic differences between NrtA and NrtB provide physiological plasticity for nitrate acquisition.
- Nitrate assimilation genes may be induced by extracellular nitrate sensing, independent of cellular entry.
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