Manipulation of yeast for transport studies: Critical assessment of cultural and experimental procedures

In the manipulation of Saccharomyces cerevisiae and other yeasts for transport studies, several factors must be taken into account. These include growth and cultural procedures, harvest, and suspension in an appropriate medium with a suitable substrate concentration. Of particular importance is suspension density, since if this is high, it may limit the availability of exogenous solute for transport and thus affect the rate of accumulation and intracellular/extracellular solute concentrations. This has been demonstrated with respect to the uptake of 2-deoxy-D-glucose (DOG) by S. cerevisiae, where a low suspension density of 0.27 μl (cell volume) ml (medium volume)^-1 resulted in a high initial rate of uptake, a higher accumulation ratio, and negligible disappearance of DOG from the external medium, contrasting with a high suspension density of 20 μl (cell volume) ml (medium volume)^-1, where the initial rate of uptake and accumulation ratio were lower, coupled with a substantial decrease in external DOG concentration. Such factors have a significant influence on the analysis and interpretation of transport data and should always be considered. Published reports of yeast transport studies should contain sufficient relevant, detailed information so that these effects can be fully evaluated.