Hello,

I am writing to ask on how to maintain positive transformants of yeast strains that are originally auxotrophic in a rich medium such as biomass hydrolysate. To my understanding, selection of positive prototrophs can be made in synthetic media supplied with the relevant amino acids except for one coded by the marker. However, I fear that upon introduction of the strain into the hydrolysate, there is a possibility of the yeast strain losing the plasmid introduced during cell growth due to the non-selecting condition. Is my fear founded and if so, can anyone suggest an approach to avoid this?

In a related work (Development of a Saccharomyces cerevisiae Strain with Enhanced Resistance to Phenolic Fermentation Inhibitors in Lignocellulose Hydrolysates by Heterologous Expression of Laccase. Larsson et al., 2001), the "hydrolysates were supplemented with yeast nitrogen base and amino acids at concentrations corresponding to those is SC-Ura medium". Would this be an acceptable approach for selection throughout fermentation?

Any input is much appreciated and I extend my gratitude for them