PHENOTYPE IN CANDIDA-ALBICANS OF A DISRUPTION OF THE BGL2 GENE ENCODING A 1,3-BETA-GLUCOSYLTRANSFERASE

The BGL2 gene encodes a unique 1,3-beta-glucosyltransferase (Bgl2p) pr esent in the cell wall of Candida albicans and other fungi. Although b elieved to be involved in cell wall assembly, disruption of the gene i n Saccharomyces cerevisiae showed no apparent phenotype. We performed sequential disruptions of the BGL2 loci in a homozygous ura3 clinical isolate of C. albicans using the URA3 blaster method, in order to inve stigate the role of Bgl2p in this dimorphic, pathogenic fungus. Strain CACW-1 contained disruptions of both homologues of the BGL2 gene and lacked Bgl2p, as assessed by protein extraction, SDS-PACE and Western blot analysis, and enzyme assay; however, residual non-Bgl2p transfera se activity was detected. CACW-1 was attenuated in virulence for mice when compared to an isogenic parent strain, and fewer organisms were r ecovered from the kidneys of infected animals. Additional phenotypic c hanges included: (1) a dramatic increase in the sensitivity to the chi tin synthesis inhibitor nikkomycin Z when CACW-1 cells were incubated at 37 or 42 degrees C; (2) an 8.7 +/- 1.6% slower growth rate at 37 de grees C for CACW-1 when compared to its isogenic parent; and (3) aggre gation of CACW-1 cells during stationary phase and/or incubation of st ationary phase cells in phosphate buffer. Characterization of SDS-extr acted cell walls did not reveal any significant differences in the lev els of 1,3-beta- or 1,6-beta-glucan. These data reveal that loss of Bg l2p does have a phenotype in C. albicans, and indicate that (1) loss o f Bgl2p function renders cells more dependent on chitin for wall integ rity, and attenuates virulence (probably due to subtle changes in walt structure), and (2) that additional 1,3-beta-glucosyltransferases are present in the C. albicans BGL2 disruptant.