Studies in carotenogenesis. 10. Spirilloxanthin synthesis by washed cells of Rhodospirillum rubrum

Abstract

Washed cells of Rhodospirillum rubrum do not synthesize spirilloxanthin when transferred to a metabolizable source of carbon. Cells grown in the presence of diphenylamine, when washed and transferred to phosphate buffer alone, under aerobic conditions in the dark, or anaerobic conditions in the light, synthesized spirilloxanthin. The amount of pigment synthesized approached that found in normal cells. Little synthesis occurred aerobically in the dark, and only small amts. in aerobic, illuminated cultures. The presence of a metabolizable carbon source did not increase the amount of pigment synthesized. Suspensions of normal cells in phosphate buffer took up little or no oxygen, whereas diphenylamine cells consumed considerable amounts of oxygen when unilluminated; less, when illuminated. Potassium ferricyanide and ferrous sulphate counteracted the slight growth-inhibitory effect of diphenylamine, and also slightly stimulated pigment synthesis. Small amounts of polyenes (including phytoene, phytofluene and [zeta] -carotene) was found in diphenylamine cultures but not in normal cultures. The amounts of these polyenes did not alter significantly when washed, diphenylamine cells were resuspended in phosphate buffer. The lipid levels in cells growing normally, and in diphenylamine cells were measured and found to be slightly lower in the latter. On resuspension, the lipid levels of washed, diphenylamine cells did not alter significantly. Washed diphenylamine cells resuspended in phosphate buffer, synthesized bacteriochlorophyll.