Changes in colony morphology were associated with the degeneration of solvent-producing strains of Clostridium acetobutylicum. The most efficient solvent-producing strains gave rise exclusively to colonies with dense centers containing large numbers of spores. Many outgrowths of various morphologies developed from the perimeter of such colonies after several days of incubation. The most degenerate cultures did not produce solvents and gave rise to large diffuse colonies that did not contain spores. These diffuse colonies did not produce outgrowths. Intermediate colony types were also observed. These could be derived from liquid cultures that were relatively poor solvent producers or from the outgrowths of colonies of efficient solvent-producing strains. Some of these intermediate types produced spores but did so less frequently than the high-solventproducing strains. The spores of the intermediate types could not be distinguished from those of the most efficient solvent producers on the basis of heat sensitivity. The relationship observed between colony morphology and solvent production provides a method for predicting the solvent-producing potential of C. acetobutylicum cultures.

A particulate fraction derived from bacterial cells stimulates septation in irradiated Escherichia coli lon mutants when added to postirradiation plating media. It was established that the particles are derived from the cytoplasmic membrane and that they have been partially purified by sucrose density gradient centrifugation. These particles also contain the cytochrome-based respiratory activity of the cell. A variety of experiments established a correlation between the septation-promoting activity of the particles and their ability to remove oxygen from the postirradiation plating medium. It was suggested that the efficient removal of oxygen from the medium allowed the lon cells to repair radiation-induced damage to the septation mechanism.

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