Identification of genes contributing to a 'High Nitrogen Efficiency' (HNE) phenotype in yeast.
Jennie Gardner (1), Miguel de Barros Lopes (2), Vladimir Jiranek (1)
(1) School of Agriculture and Wine, The University of Adelaide, PMB 1, Glen Osmond, SA, 5064, Australia; (2) School of Pharmacy and Medical Sciences, Division of Health Sciences, University of South Australia, GPO Box 2471, Adelaide, SA, 5001, Australia
In recognition of the importance of assimilable nitrogen in the successful completion of several fermentation processes we have sought to develop yeast strains that utilize this typically limited nutrient more efficiently. With the aid of transposon mutagenesis and a high throughput method for analysis of multiple fermentations, we have identified 'nitrogen efficient' mutants that catabolise more sugar for a given amount of nitrogen utilized. In this way we identified two genes, NGR1 and GID7, whose disruption leads to enhanced catabolism of glucose by an industrial strain and/or laboratory strain, during anaerobic growth in a medium with limiting nitrogen. Fermentation profiles were also evaluated with moderate or excess nitrogen supplied as either ammonia, or a mix of amino acids and ammonia. Deletion of NGR1 or GID7 altered the amounts in which major metabolites were produced, and in ngr1 strains, decreased biomass yield. Transcript levels of a selection of key central nitrogen metabolism genes were determined by real time PCR for fermentation samples. Deletion of either GID7 or NGR1 caused an increase in transcript abundance of both GLT1 and GLN1 and a decrease of GDH1, thereby suggesting an affect on central nitrogen metabolism. In addition, the deletion of GID7 caused an increase in the transcript abundance of GDH2.