Identification of (1-->6)-beta-D-glucan as the major carbohydrate component of the Malassezia sympodialis cell wall.

Members of the genus Malassezia are commensal fungi found on the skin of both human and domestic animals and are associated with skin diseases including dandruff/seborrheic dermatitis, pityriasis versicolor, and atopic eczema (AE) in humans. In this study we have characterized the cell-wall carbohydrates of Malassezia sympodialis, one of the species most frequently isolated from both AE patients and healthy individuals. Cells were grown in liquid Dixon media at 32 degrees C, harvested, and processed using a standard Fehling's precipitation methodology for the isolation of mannan and a standard base/acid extraction for (1-->3)-beta-D-glucans. Using these classic extraction methods we were unable to isolate precipitable mannan or insoluble (1-->3)-beta-D-glucan. However, acidification and addition of methanol to the remaining Fehling's-treated sample resulted in a very clean precipitate. This material was characterized by GPC-MALLS, 1D and 2D NMR, and GC-MS for monomer-type and linkage-type composition. We determined that trace amounts of both mannan and branched (1-->3, 1-->6)-beta-D-glucan were present in the recovered precipitate, but not linear (1-->3)-beta-D-glucan. Surprisingly, NMR analysis indicated that (1-->6)-beta-D-glucan was the major carbohydrate component isolated from M. sympodialis cell wall. GC-MS linkage analysis confirmed the (1-->6)-beta-D-glucan structure. Based on these studies we have determined that the M. sympodialis cell wall contains (1-->6)-beta-D-glucan as the major carbohydrate component along with trace amounts of mannan and (1-->3, 1-->6)-beta-d-glucan. In addition, these data indicate that modification of the classic mannan isolation methodology may be useful in the simultaneous isolation of both mannan and (1-->6)-beta-D-glucan from other fungi.