DRUG-RESISTANCE IN YARROWIA-LIPOLYTICA

Six strains of Yarrowia lipolytica tested here were resistant to 10-20 g erythromycin or chloramphenicol per L glycerol-agar medium. Cells t olerating 4 g chloramphenicol per L were very rare and reverted rapidl y to the highest resistance. In analogy with Ery(R) mutants of Kluyver omyces lactis, our strains did not grow at 36 degrees C but did not lo se their viability at that temperature. Two levels of resistance were found with oligomycin and antimycin A, i.e. 10 and 3 mg/L in the forme r and 10 and 2 mg/L in the latter. The higher resistance levels segreg ated mitotically and were, therefore, controlled extrachromosomally. T he lower resistance levels showed very frequent changes from sensitivi ty to resistance that prevented the genetic analysis of this resistanc e. An almost continuous range of tolerance to <5-400 mu g mucidin per L was found in populations of the strains analyzed. Newly formed Muc(R ) cells were established only in the presence of the antibiotic. Pure cultures of Muc(R) cells showed an extremely high instability caused b y their lower viability and very low growth rate in the absence of muc idin. No loss of resistance to antimycin A was found, although Ant(R) cells revealed similar negative selection. Mutability Muc(S) --> Muc(R ) and Muc(R) --> Muc(S) was higher in Ant(R) cells than in Ant(S) ones .