MET15 as a visual selection marker for Candida albicans

To develop better molecular genetic tools for the diploid yeast Candida alb icans, the suitability of the METIS gene as a visual selection marker was s tudied. Both METIS alleles of C. albicans CAI-4 were isolated by functional complementation of a Saccharomyces cerevisiae strain lacking the METIS gen e. Growth of this complemented strain on Pb2+-containing medium was associa ted with a colour shift of brown into white colonies. The METIS alleles of C. albicans were located on chromosome 4 by pulsed-field gel electrophoresi s and Southern blotting. A met15-deficient strain of C. albicans CAI-4 was generated using the ura blaster technique. This strain showed a brown colon y colour on Pb2+-containing medium, which corresponded with the colony colo ur of a S, cerevisiae strain lacking the METIS gene. Unexpectedly, the met1 5-deficient strain of C. albicans still grew on methionine-depleted medium. However, this growth was severely delayed. In addition, complementation of this strain with an integrative or replicative plasmid containing either o f the METIS alleles resulted in the formation of white transformants on Pb2 +-containing medium. These transformants grew very well on methionine-deple ted medium. Colony sectoring was obtained with the replicative plasmid and not with the integrative one. This study demonstrates that the METIS gene o f C, albicans is suitable as a visual marker and therefore can be used to i dentify transformants and study plasmid stability. GenBank Accession Nos fo r MET15 nucleotide sequences are AF188273, AF188274 and AF188275, Copyright (C) 2000 John Wiley & Sons, Ltd.