SUMMARYHeat-killed whole cells, purified cell walls, and the three main polymers isolated from cell walls of Mycobacterium sp. ATCC 607, M. smegmatis AliCe 14468 and M. phlei ATCC 11758, were examined to find the receptor sites for phage GS-7. Among heat-killed whole cells of insusceptible species, M. srnegmatis adsorbed the phage at a higher rate than the susceptible Mycobacterium sp. ATCC 607, whereas M. phlei did not adsorb the phage at all suggesting a distinction between phage-resistance (absence of receptor) and phage-immunity (presence of both receptor and repressor).Each of the three polymers of the cell wall (the lipopolysaccharide of the outer layer, the lipopolysaccharide-lipoprotein complex of the middle layer and the lipopolysaccharide-mucopeptide or mucopeptide complex of the inner layer) contain receptor substances. The lipopolysaccharide moiety isolated from the lipopolysaccharide-lipoprotein complex adsorbed phage at the same rate as the whole complex; implying that the possible receptor substances were the lipopolysaccharide moieties of the three polymers. Delipidation of both cell wall and the lipopolysaccharide-mucopeptide complex resulted in a loss of phage-adsorbing capacity, suggesting that the lipid portion of the lipopolysaccharides may constitute the phage receptors.

The taxonomy of murine leprosy bacillus, as a species of genus Mycobacterium, is not yet established. Based on morphological characteristics during limited growth in vitro, Uyeda (4) argued that this microorganism should not be classified as a mycobacterium, but rather should be in a new genus related to Nocardia. However, the chemical composition of the cell wall (arabinose, galactose, and mucopeptide) is qualitatively similar to that of other mycobacteria (1). Since a

N-methyl-N'-nitro-N-nitrosoguanidine, which is known to be a very effective mutagen in many systems, was used to induce mutants in the yeastlike form of Paracoccidioides brasiliensis strain IVIC Pb9, an imperfect fungus. Forty-three auxotrophic and 27 prototrophic morphological mutants were isolated after treatment with 50 ug of nitrosoguanidine per ml in 0.1 M citrate buffer, pH 5.0. Auxotrophic mutants required primarily either amino acids, purines, or pyrimidines. Some auxotrophs were also morphological mutants. The main morphological difference from the parental strain was the texture or the color of the yeastlike colonies. Only one prototrophic morphological mutant differed in the size and form of the yeastlike cells when compared with the parental strain. Auxotrophic mutants were used in pairwise combinations to attempt heterokaryon formation without success.