deoxy-galactose inhibition anomaly

[Chris Skory]

I have been trying to use 2-deoxy-galactose (DG) to isolate gal 
mutants in the yeast Candida wickerhamii.  Some interesting 
things have occurred with just trying to inhibit the cells with 
the DG.  When using standard protocols of plating the yeast on 
YNB (2 % glycerol, 0.5 % DG), we still get growth with multiple 
phenotypes appearing.  The majority of the colonies are small and 
there are several different looking big colonies within the 
small.  This is definitely a pure culture taken from a single 
colony.   Replating any of the big colonies yields an identical 
looking big colony (ie: plating 3-4 different looking big 
colonies on the same plate results in plate of seemingly pure 
culture of big colonies).  Replating a single small colony 
results in phenotype mix similar to the first plate.

Total inhibition of all cell growth was finally achieved by 
substituting sucrose for the glycerol.  However, the same mixed 
phenotypic growth still occurred if the sucrose/DG mix was used 
with complex medium (eg yeast extract, peptone).  

Does anyone have any idea of what could be occurring here.   
Could this be a petite effect or a ploidy effect?   I am at a 
loss as to what is happening.  Any suggestions would be 
appreciated.

Christopher D. Skory, Ph.D. 		 
Research Microbiologist

National Center for Agricultural	        
  Utilization Research, USDA-ARS 	             
Fermentation Biochemistry Unit 
Peoria, Illinois 61571-3902       

E-mail:  skorycd at ncaur1.ncaur.gov