Directed Evolution of Metabolic Pathways in Microbial Populations II. a Repeatable Adaptation in SACCHAROMYCES CEREVISIAE.

A selection experiment was conducted for approximately 1,000 generations in a chemostat population of 10(9) cells of the haploid yeast, S. cerevisiae. The experiment was designed to enhance genetically the rate at which the external enzyme acid phosphatase catalyzed the hydrolysis of very low concentrations of beta-glycerophosphate at an unfavorably high pH. The observed genetic adaptation in this experiment consisted of a mutation (ACP-2) in the acid phosphatase structural gene which effected a shift in the pH optimum of the enzyme and incremented its activity. The effects of ACP-2 and a similar mutation, ACP-1, on acid phosphatase substrate specificity are also reported.