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
.