Anomalous morphogenetic events in yeasts exposed to the polysaccharide-binding dye Congo red

When exposed to Congo red, Rhodotorula glutinis halts cell proliferation, whereas Saccharomyces cerevisiae continues to bud; however, the separation between mother and daughter cells is impeded. Both yeasts develop diverse wall and septum abnormalities due to the accumulation of amorphous materials instead of chitin microfibrils. In Saccharomyces, the original wall frequently breaks and numerous vesicles, probably of secretory nature, are visible in the cytoplasm. The microorgamisms employed react differently to Congo red exposure due to the different roles that chitin plays in their walls. To explain why Congo red forces chitin synthase to form excessive amounts of N-acetylglucosamine chains with a random distribution, a model is proposed in which multienzyme complexes dissociate into single units since the polymers under synthesis, with the dye attached, can not assemble regularly. Each enzyme subunit continues to form glucan chains while it moves freely and randomly along the plasma membrane.