Ultrastructure of acapsular mutant Cryptococcus neoformans cap 67 and monosaccharide composition of cell extracts

Abstract

Acapsular mutant Cryptococcus neoformans cap 67 was grown in Pine's citrate broth medium for 3 days and the cells then transferred to a nitrogen-free medium for 6 days. The cells were subjected to a four stage extraction with buffered Triton-X1OO, cold dilute alkaline borohydride, hot dilute acetic acid, and a second alkaline extraction. Galactoxylomannan antigens were recovered from the culture supernates of both 3 day old and 9 day-old yeast cells. The alkaline extracts contained water-soluble galactoxylomannan and a water-insoluble glucan. Dilute acid treatment released a minor amount of carbohydrate from the cells. The second alkaline extraction yielded increased amounts of glucan and galactoxylomannan from the 9 day-old cells. Soluble non-dialyzable cell extracts were antigenically identical in immunodiffusion with the culture supernate antigens. After the extraction sequence, all of the galactose, xylose, and mannose were removed from the cells. The walls retained their shape after extraction but their layers were loosened. Cells resuspended in nitrogen-free medium for six days developed thickened walls with alternating electron-dense and electronlucent layers. The major constituent of the thickened 9 day-old cell walls was glucose, only 5% glucosamine was detected.