Photopharmacology. V: Influence of sun's rays on growth of yeast in sodium benzoate.

Abstract

Growth of yeast cells in sugar solutions, in light and darkness was studied by measurements of CO₂ evolved. Uniform suspensions of Fleishman's baking yeast were made in solutions of glucose or more often of sucrose, and the growth in sunlight and in the dark at the same temperatures was studied in two sets of fermentation tubes. Ordinarily suspensions of 0.5 or 1 per cent by weight of yeast in a 5 per cent or 10 per cent solution of sugar was employed. It was found that fermentation took place more rapidly in the dark than in the light, at the same temperature. The effect of sodium benzoate on the growth of yeast and fermentation was studied by adding the drug in concentrations of 1:1500 to 1:500. It was found that sodium benzoate in concentration of 1:1000 produced practically no inhibition in the growth as compared with normal yeast suspensions when kept in dark- and that even concentration of 11500 of benzoate caused but very slight inhibition of growth in the dark. On the other hand when exposed to direct sunlight even 1:1000 and 1:1250 of sodium benzoate produced a distinct retardation of fermentation, and the degree of inhibition was very much greater than in control experiments with sunlight alone, without the benzoate. The inhibitory action of the sodium benzoate was increased a hundred and more per cent in the light. In diffuse sunlight, growth of yeast in benzoate was also less than in darkness at the same temperature.

Examination of the glass from the fermentaticon tubes by spectro-photography with a mercury vapor quartz lamp revealed that it was permeable to wave lengths as short as 3000 Angstrom units. By the use of suitable filters in connection with the above experiments ilt was found that it was the shorter rays of the sun, that is, those which were cut out by amber and brown colored filters which were respnsible for the above photosensitizing effect on sodium benzoate.