Mutants of Kluyveromyces lactis with altered protein glycosylation are affected in cell wall morphogenesis.

We isolated spontaneous mutants resistant to sodium orthovanadate in the biotechnologically significant yeast Kluyveromyces lactis. Resistance behaved as a recessive character in all mutants analyzed. Four genes were defined by complementation analysis, from vga1 to vga4. These mutants showed defects in N-linked as well as O-linked glycosylation processes. In addition, the mutants exhibited sensitivity to the aminoglycoside hygromycin B and to calcofluor white, with the exception of vga4; this mutant grew in the presence of the antibiotic as well as the parental wild type and was resistant to calcofluor. The mutations were accompanied by alterations in the cell wall structure, as revealed by the delocalization of chitin, changes in cell shape and size and by the clumpy aspect of the cultures. The mutants isolated provide basic tools for molecular and cellular analysis of glycosylation processes in K. lactis.