Chromogenesis by three members of the genus was studied. The species investigated were: and All were capable of pigment production, but each species required a different set of factors for chromogenesis. All needed cysteine and ferrous sulphate. These factors sufficed for pigment production by Additional vitamin K was essential for pigment production by both and , but the latter also required haemin.

Pigment production by was studied in two media: 5 per cent. horse blood agar, and an agar-free partially defined medium. The pigment was harvested from these media, purified and subjected to chemical analysis. This pigment, previously thought to be haemin, proved to be colloidal ferrous sulphide.

The pigment produced by two other species, and , examined in the same way also proved to be colloidal ferrous sulphide.


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