Dimorphism inBenjaminiella poitrasii: Involvement of intracellular endochitinase andN-acetylglucosaminidase activities in the yeast-mycelium transition

The chitinase andN-acetylglucosaminidase activities in cell-wall-bound and free fractions in the dimorphic fungusBenjaminiella poitrasii were studied as a function of morphological (unicellular yeast-mycelium) transition. The specific activities of chitinases of cell-wall-free, particularly in the membrane fraction, were significantly different in the yeast and mycelial forms. During the yeast-mycelium transition, theN-acetylglucosaminidase activity isolated in a membrane preparation increased steadily. The activity of the yeast cells (0.83±0.17 nkat/mg protein) increased 17-fold to 14.2±1.7 nkat/mg protein in 1-d-old mycelial cells. The endochitinase activity increased 12-fold between 6 and 12 h and thereafter practically remained unchanged up to 24 h. A reverse trend in the chitinolytic activities was observed during the mycelium-yeast transition. Isoelectrofocussing (pH range 3.5–10) of mixed membrane fraction free of particulate fraction of parent and morphological (y-5, yeast-form) mutant cells separated endochitinase andN-acetylglucosaminidase activity into two pH ranges,viz. 4.3–5.7 and 6.1–7.7, respectively. The predominantN-acetylglucosaminidase activity observed at pH 6.9 and 7.1 for the parent strain membrane fraction was undetected in the mutant preparation. The results suggested that the membrane-bound (either tightly or loosely) chitinolytic enzymes, particularly,N-acetylglucosaminidase, significantly contributed to the morphological changes inB. poitrasii.