Hyphal walls of Aspergillus phoenicis and Sclerotium rolfsii are composed of large amounts of glucose-and N-acetylhexosamine-containing polysaccharides, and the walls are extensively digested by streptomycete culture filtrates or by a mixture of purified chitinase and #-(I-.3) glucanase preparations with the release of the monomeric units. A. phoenicis conidial walls also contain polymers of glucose and N-acetylhexosamine, but these walls are resistant to digestion by microorganisms or the enzyme combination active on the hyphae. When the melanin-containing spicules were removed from the spore surface, however, the chitinase and glucanase partially digested the underlying structural components. Microorganisms decomposing hyphal walls of S. rolfsii did not attack the melanin-covered sclerotia produced by this fungus. No microorganism capable of lysing two fungi, Rhizoctonia solani and Cladosporium sp., producing hyphae containing abundant melanin was found. The ecological significance of these findings and possible mechanisms for the protective influence associated with melanins are discussed.

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The test organism, a Bacillus species isolated from soil, behaved as a typical cation exchanger having a CEC of 95 meq/100‐g organism (oven‐dry weight). Increasing acidity from pH 6.6 to 4.5 greatly reduced the number of surviving cells suspended for 3 hours in an acetate buffer. Addition of soluble aluminum up to 80 ppm produced no further detrimental effect upon the organism, even though the cell walls of the organism were saturated with aluminum. Exchangeable aluminum in the form of Al‐saturated Wyoming bentonite decreased the number of surviving cells as compared with a Ca‐ saturated Wyoming bentonite. Addition of soluble Al to the Al‐clay suspension did not result in any interaction. Upon incubation with the clay suspensions, the organism changed its gram‐staining characteristic. Clay particles in all treatments were adsorbed by the cells producing organism‐clay aggregates.