Morphological Changes and Resistance induced in Saccharomyces pastorianus by the antibiotic cycloheximide

Abstract

SUMMARY: The growth of Saccharomyces pastorianus was 50% inhibited by 0.013 p.p.m. cycloheximide, and completely inhibited by 0.100 p.p.m. in liquid medium after 24 hr. at 280. At subinhibitory concentrations of cycloheximide abnormally large cells and cell aggregates were formed, probably as a result of interference by cycloheximide with the synthesis of structural cell-wall materials. When S. pastorianus was grown in media with successively higher concentrations of cycloheximide partially resistant organisms were developed. These did not form aggregates and giant cells in the presence of cycloheximide, but on back inoculation to cycloheximide-free media they were ‘slow growers’ and formed small colonies on nutrient agar. After a few transfers on cyclo heximide-free media the resistant organisms reverted to the normal ‘fast growing’ type. The resistance to cycloheximide was not the result of any acquired ability to decompose or inactivate the compound.