Characterization of the carbohydrate component of fraction I in the Neurospora crassa cell wall

Abstract

The carbohydrate portion of fraction I of the Neurospora crassa cell wall has been analyzed for sugar composition by gas-liquid chromatography and colorimetric methods. The analysis was performed comparatively in a wild-type strain (RL 3-8A) and three morphological mutants: scumbo (FGSC 49), peak-2a (a mutant known to be allelic to biscuit), and ragged (FGSC 296). Fraction I of all strains studied contains glucose, mannose, and galactose as the main sugars. Uronic acids and amino sugars are also present in small amounts. The glycosidic linkages binding the neutral sugars were analyzed by Lindberg's combined gas chromatography-mass spectrometry techniques for identification of the partially methylated alditol acitate sugar derivatives. The main polymeric portion of fraction I seems to be a linear glucan with the glucose residues linked by 1 leads to 3 and 1 leads to 4 bonds. A mannan portion with a branched configuration is also present, with galactose as the sugar residue which serves as branches in the molecule(s). The branched mannan portion appears to increase in amount in correlation with more drastic morphological changes of the mycelia. In this respect, the mutant ragged has the lowest mycelial growth rate and the largest amount of mannan. The importance of the polysaccharide structure of fraction I on the colonial morphology of the mycelia is discussed.