Small Colonies of Clostridium sticklandii Resulting from Nitrosoguanidine Treatment and Exhibiting Defects in Catabolic Enzymes.

Several strains of Clostridium sticklandii, isolated from small colonies arising after treatment with 1-methyl-3-nitro-1-nitrosoguanidine, exhibited markedly depressed activities of certain catabolic enzyme systems known to provide energy to the organism in the form of adenosine triphosphate. In some of these strains the levels of glycine reductase, the ability to ferment lysine to fatty acids and ammonia, and formate-dependent 2,3-5-triphenyltetrazolium chloride reduction were only 0 to 10% of that of the wild type. Another subgroup of mutants exhibited activities of some of these enzymes from 1.3 to 3 times higher than those of the wild type. Small-colony mutants of an obligate anaerobe, like those of oxygen-utilizing organisms, can therefore be due to defects in one or more of their energy-providing systems. The merits of small-colony formation as an auxiliary marker for the isolation of catabolic mutants are discussed.