Cytological structure of Aspergillus niger by electron microscopy

Distribution and conformation of crystalline nigeran in hyphal walls of Aspergillus niger and Aspergillus awamori

Hyphal walls of Aspergillus awamori containing increased amount of the alpha-glucan, nigeran, became correspondingly more opaque when viewed in the electron microscope as shadowed preparations. However, increased polymer deposition was not accompanied by any significant change in wall thickness. The nigeran of both A. awamori and Aspergillus niger occurred in situ in a crystalline conformation identical to that of single crystals prepared with pure polysaccharide. Furthermore, this polymer was the dominant crystalline material in the hyphae whether or not they were enriched in nigeran. Enzymic digestion of nigeran in A. niger and A. awamori revealed that the bulk of the polymer was exposed to the cell's exterior. However, a certain fraction was accessible to enzymic attack only after the wall was treated with boiling water. A third portion, detectable only by x-ray diffraction, was associated with other components and could not be extracted, even with prolonged boiling. It was removed by hot, dilute alkali and was associated in the wall with another glucan fraction. Dry heating of A. niger walls altered their susceptibility to enzymic digestion of nigeran in situ. It is proposed that this treatment introduces interstices in the crystal surface that facilitate attack.

Structure and composition of the cell wall of Neurospora crassa

The structure and composition of the cell walls of hyphae of Neurospora crassa were investigated by electron microscopy, chemical analysis, and X-ray diffraction both before and after progressive enzymatic degradation by snail gut enzymes, chitinase, and trypsin. The wall consists of two phases: randomly disposed skeletal microfibrils of chitin only and an amorphous matrix which contains both beta-glucans and protein. The protein contains a high percentage of the amides of aspartic and glutamic acid but no hydroxy-proline or cysteine. A portion of this protein is a component of or is associated with a system of pores which is embedded in the matrix of the wall. These pores, 40 to 70 A in outside diameter, sometimes branch and seem to provide a three-dimensional network from one side of the wall to the other. They may be a general system of transport across the walls.