A mutant of Saccharomyces cerevisiae temperature sensitive for flocculation. Influence of oxygen and respiratory deficiency on flocculence

Abstract

A flocculent strain of Saccharomyces cerevisiae, containing the dominant gene for flocculence FL04, was mutagenized with N-methyl-N′-nitro-N-nitrosoguanidine. Non-flocculent mutants were isolated with a selection procedure based on the slower sedimentation of non-flocculent cells. One closer studied mutant was due to an unlinked suppressor mutation for FL04. This suppressor gene is designated sufl. The gene sufl is neither centromere linked nor linked to his4 or the mating type locus. The gene sufl behaves as a recessive in some diploids and as a dominant in others, illustrating the genetic complexity of the flocculation phenomenon. The mutant was found to be non-flocculent after growth at 30°C whether aerated or not. At 22°C the mutant was flocculent in the absence of aeration during growth, but non-flocculent with aeration or supplementation of the growth medium with ergosterol and unsaturated fatty acids. None of several inhibitors of mitochondrial functions had any effect on the expression of flocculence. A number of petites induced in the mutant strain with ethidium bromide had altered flocculation phenotypes. A method for measuring flocculence using the spectrophotometer is described. © 1978 Carlsberg Laboratory.