Fractionation of carbon isotopes by Ectothiorhodospira shaposhnikovii during photomixotrophic growth

Fractionation of carbon isotopes by the bacterium Ectothiorhodospira shaposhnikovii was studied during its photomixotrophic growth on acetate (delta(13)C = -36.6 parts per thousand) and sodium bicarbonate (delta(13)C = -8.2 parts per thousand). It was shown that the carbon isotope composition of bacterial biomass essentially inherited that of acetate as the main carbon source. The content of C-13 in bicarbonate tended to decrease during mixotrophic growth of the bacterium due to the production of CO2 in the course of acetate metabolism. The metabolically produced carbon dioxide, as well as the cell biomass, had a carbon isotope composition close to that of acetate. Distribution of carbon isotopes in the main cellular fractions followed the pattern previously described for the photoautotrophically grown bacterium: the lipids were depleted of C-13 by -2 parts per thousand relative to the biomass and -4 parts per thousand relative to the protein and carbohydrate fractions.