Metachromatic Granules of Microorganisms'

The exact nature and function of the metachromatic (volutin) granules seen in many microorganisms is still a matter of conjecture although polymetaphosphates (polymers of highenergy anhydride-linked phosphates) are a known constituent. The object of this paper is to re-examine volutin as a cytological entity, and to present a working hypothesis on the mechanism of formation of this substance. The metachromatic granules (volutin) of microorganisms are usually considered to be a reserve source of food; their formation during periods of phosphate uptake has been noted (Lewis, 1941; Nagel, 1948). The pioneer work of Wiame (1946; 1947a, b, c; 1949) on Saccharomyces cerevisiae developed chemical criteria for the recognition of volutin, establishing this substance as a polyphosphate, the stainable chromotropic form (Michaelis, 1947) probably existing in the cell as a polymer of a hexametaphosphate unit. Hexametaphosphate has since been shown to be a mixture of polyphosphates of varying chain lengths (Kornberg et al., 1956). Whether intracellular metaphosphate is free or bound in an organic complex has been a moot question (Ingleman, 1950). Schmidt (1951) pointed out that (a) there was no evidence for binding with proteins or a close association with nucleates and (b) differences in extractability of metaphosphate with trichloroacetic acid could simply reflect diffusion properties of the cell. However, both qualitative and quantitative differences between the acid-soluble and the acid-insoluble (presumably bound) metaphosphate fractions of growing yeast cells have been demonstrated (Juni et al., 1947, 1948; Katchman and Fetty, 1955). There is a variety of opinion on the constitution and location of the volutin granules: 1. Volutin (in yeast) is metaphosphate, occurs