Incorporation of tritium into cell materials of Rhodopseudomonas spheroides from tritiated water in the medium under aerobic conditions.

When Rhodopseudomonas spheroides cells grown aerobically in the dark were incubated in medium containing tritiated water (THO), incorporation of T into the bacterial cell materials occurred under growth and no-growth conditions. The overall T incorporation under no-growth conditions was stimulated by vigorous aeration and was suppressed strongly in the presence of either 10(-3) M KCN or 0.3% HgCl2, indicating that the bulk of the incorporation might depend upon bacterial cell metabolism or respiration. 10 mug/ml chloramphenicol and 20 mug/ml rifamipicin slightly suppressed the T incorporation. The extent of T incorporation was proportional to the concentration of T in the medium. Accordingly, regardless of differences in the concentration of T in the medium, the maximum ratio of T content per hydrogen atom in the cell materials to that of THO in the medium was approximately 0.2 in non-growing cells and 0.5 in growing cells, whereas the value was 0.02-0.03 in cells incubated in medium containing KCN or HgCl2. The non-growing cells aerated in THO medium were lyophilized and fractionated by the modified method of Schneider. More than 40% of the total T incorporated into the cell materials was recovered in the cold PCA-soluble fraction, whereas the distribution of T into fractions solbule in ether-ethanol, hot PCA and alkali was 10 to 20% each. More than 75% of the T extracted in the cold PCA-soluble fraction was volatile. While the amounts of RNA and protein in the non-growing cells decreased on adding chloramphenicol or rifampicin, the distribution of T in these fractions did not change much. Our results on T incorporation into non-growing cells indicate that the major T incorporation into bacterial cell materials is independent of biosynthetic reactions using labeled precursors produced by the assimilation of T into metabolites, but presumably depends on energy-linked conformational changes of macromolecules.