THE SIGNIFICANCE OF ACTIVE FRUCTOSE TRANSPORT AND MAXIMUM TEMPERATUREFOR GROWTH IN THE TAXONOMY OF SACCHAROMYCES-SENSU-STRICTO

Eighty five strains representing the four sibling species currently re cognized within the Saccharomyces sensu stricto group were tested for the capacity to transport fructose by an active proton symport. Active transport of fructose was not detected in the strains of Sacch. cerev isiae and Sacch. paradoxus, whereas it was found in the strains assign ed to Sacch. bayanus and Sacch. pastorianus. The maximum temperature f or growth (T-max) of the latter two species ranged from 30 degrees C t o 34 degrees C and from 28 degrees C to 35 degrees C respectively, at variance with the ranges of T-max values of Sacch. cerevisiae (35 degr ees C-43 degrees C, with one exception showing a lower T-max) and Sacc h. paradoxus (35 degrees C-41 degrees C). The identity of the strains has been defined by DNA/DNA reassociation studies and their genome siz e estimated from the kinetics of DNA renaturation. The data support ea rlier reports of the intraspecific heterogeneity of Sacch. cerevisiae and of dose relationships between species. This work represents an ext ension of our initial investigation of sibling Saccharomyces species. While showing that active fructose transport is a suitable systematic character for rapid differentiation of the two subgroups within Saccha romyces sensu stricto, useful differential tests to be applied within each subgroup were not found.