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Evidence for multiple nitrate uptake systems in the yeast Hansenula polymorpha.
F Machín1, G Perdomo, M D Pérez
1Departamento de Bioquímica y Biología Molecular, Grupo del Metabolismo del Nitrógeno-Consejo Superior de Investigaciones Científicas, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Canary Islands, Spain.
FEMS Microbiology Letters
|February 13, 2001
Summary
Even without the main nitrate transporter (YNT1), Hansenula polymorpha can still absorb nitrate. A new system identified an additional nitrate uptake pathway, potentially also transporting nitrite.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Hansenula polymorpha utilizes nitrate as a nitrogen source, relying on specific transporter proteins.
- The high-affinity nitrate transporter gene, YNT1, has been identified, but its absence doesn't fully abolish nitrate uptake.
Purpose of the Study:
- To identify additional nitrate transporters in H. polymorpha responsible for nitrate uptake in YNT1 mutants.
- To characterize the properties of this novel nitrate transport system.
Main Methods:
- Construction of a modified H. polymorpha strain (FM31) with a disrupted nitrate assimilation gene cluster and a nitrate reductase gene (YNR1) under a strong promoter.
- Quantification of nitrate uptake in the FM31 strain under various conditions.
- Assessment of the influence of nitrogen sources (ammonium, glutamine) and inhibitors (chlorate) on nitrate uptake.
Main Results:
- Nitrate uptake was detected in the FM31 strain, independent of YNT1 and another transporter (Yna1p).
- This uptake was not induced by nitrate or repressed by reduced nitrogen sources.
- Inhibition of nitrite extrusion by external nitrite suggested the transporter might also mediate nitrite uptake.
Conclusions:
- H. polymorpha possesses at least one additional nitrate uptake system beyond YNT1.
- This newly identified system exhibits distinct regulation compared to known transporters.
- The transporter may play a role in both nitrate and nitrite uptake, suggesting a broader role in nitrogen assimilation.