Cell wall composition of the aquatic fungus Blastocladiella emersonii

Abstract

Cell walls from Blastocladiella emersonii were isolated by repeated washing and centrifugation. Purity and uniformity of cell wall preparations were assessed by light and electron microscopy and chemical reproducibility. Electron microscopy showed the cell walls to consist of an inner microfibrillar network and an outer amorphous layer. Analyses by X-ray and infrared spectroscopy were consistent with chitin as the major wall component. Gross chemical analysis indicated that the cell walls were composed of 74.7% amino sugar (as anhydro N-acetylhexosamine), 10.7% neutral sugar (as anhydro hexose), 10.6% protein, and 4.2% lipid. Analysis of the neutral sugars showed that isolated cell walls contain 1.5% mannose, 3.0% galactose, and 3.0% glucose. Isolated cell walls were fractionated using a hot sodium dodecyl sulfate (SDS) extraction followed by either Pronase digestion or hot KOH extraction. The hot SDS extract was found to contain two polymer types, galactose- and/or glucose-containing polymers and glycoprotein. However, the residue from the hot SDS extraction still contained most of the neutral sugars and protein present in the isolated walls. Both Pronase digestion and the hot potassium hydroxide extraction removed all of the neutral sugars except glucose. The cell wall fractionation results indicate that the major wall component is microfibrillar chitin. The results further suggest that the SDS-solubilized glycoproteins and neutral sugar polymers may represent an outer amorphous layer.