The synthesis of porphyrins and bacteriochlorophyll by cell suspensions of Rhodopseudomonas spheroides.

Free porphyrins are formed by growing cultures of some bacteria and yeasts under conditions in which formation of cytochromes is limited. With Corynebacterium diphtheriae, production of both porphyrin and toxin is dependent upon the concentration of iron salts in the medium; increasing this beyond a critical point decreases both porphyrin and toxin production (Pappenheimer, 1947). Cells grown with iron at concentrations sufficiently high to prevent accumulation of porphyrin contain considerably more cytochrome than those grown under conditions favouring porphyrin formation (Pappenheimer & Hendee, 1947; Rawlinson & Hale, 1949). Bacillus cereus excretes porphyrin (probably coproporphyrin) into the media when grown anaerobically, but only traces of porphyrin occur in aerobic cultures; the concentration of haem compounds in the cells grown anaerobically is considerably smaller than in those from aerobic cultures (Schaeffer, 1952a, b). There have been many observations of porphyrin formation by yeasts (see Lemberg & Legge, 1949). Stich & Eisgruber (1951) found that the amount of coproporphyrin Type I in cells of Saccharomyces anamensis is increased 5to 10-fold by addition of pantothenate to the growth medium, while addition of riboflavin completely suppresses porphyrin formation. Cells grown under conditions which favour porphyrin formation contain little or no haem derivatives, whereas those grown with riboflavin and iron are rich in these substances. Porphyrins may also be precursors of chlorophyll. Induced mutant strains of Chlorella, which are unable to synthesize chlorophyll, form large quantities of protoporphyrin, as well as magnesium protoporphyrin and magnesium vinyl pheophytin a5, when grown in the dark on a glucose--salts medium (Granick, 1948a, b, 1950). Another mutant produces a number of porphyrins containing up to eight carboxyl groups in each molecule, those with two such groups being predominant (Bogorad & Granick, 1953a; Granick, Bogorad & Jaffe, 1953). These observations of porphyrin formation by micro-organisms have been made with growing