Hemin-deficient mutants of Escherichia coli K-12

The occurrence of hemin-deficient bacterial mutants became known in 1953, when Jensen and Thofern (3) were able to isolate, by using streptomycin, a hemin-requiring mutant of Staphylococcus aureus. By their ability to grow as "small colony variants" (SCV), forming dwarf colonies in the absence of hemin, these mutants differ sharply from genuine conditioned lethal auxotrophic mutants, and resemble "leaky" mutants. [In this paper, SCV will be designated as Ncf(normal colony formation-deficient) mutants, a designation recently suggested by A. Slsarman and T. Horodniceanu (5).] "Leakiness" in this instance is, however, a phenotypic character, inasmuch as it is not determined by the type of mutation but rather by the ability of the cell to dispense to a certain extent with the cytochrome system. (This "pseudoleaky" character in Hemmutants of S. aureus might prove to express a general characteristic of most respiratory mutants of bacteria.) It goes without saying that, apart from the absence of compounds containing the porphyrin nucleus, the prominent feature of these mutants is their normal development in the presence of hemin. In 1957, Beljanski and Beljanski (1) described a hemin-requiring mutant of Escherichia coli M; the mutant had been selected by means of streptomycin. This mutant failed to synthesize catalase and cytochromes, displayed respiratory deficiency, and grew poorly on the usual culture media. Under special circumstances (e.g., anaerobiosis or, on the contrary, intensely aerated broth culture), hemin increased growth or catalase synthesis, but the surface growth of the mutant was not affected. In our studies on Ncfmutants of E. coli K-12 (obtained after selection with neomycin), we noticed that one class of these mutants formed normal colonies on medium supplemented with 50 ,ug (per ml) of A-aminolevulinic acid (A-ALA). These A-ALAmutants (SHSP8, SHSP14, and SHSP15) reminded us of similar mutants, de-