Metabolism of fructose in Thiocapsa roseopersicina

Thiocapsa roseopersicina strain 6311 grew phototrophically in a mineral medium containing fructose as sole electron donor and carbon source with a doubling time of 11--13 h, provided the mineral medium contained vitamine B12 (50 ng/ml), not more than 20 mM phosphate, and the culture was preincubated in the dark for 24 h. In fructose-grown cells but not in autotrophically grown cells, the cell-protein content was strongly reduced when vitamine B12 was growth limiting, while the carbohydrate content was increased. Growth on fructose as sole carbon source was inhibited by the addition of sulfide or thiosulfate; growth inhibition was relieved in the presence of bicarbonate. No growth on fructose was observed anaerobically in the dark; aerobic growth in the dark was poor. Analysis of enzyme activities in fructose- and acetate-grown cells indicated that fructose was catabolized via fructose-1-phosphate and the EMBDEN-MEYERHOF pathway. The operation of the EMBDEN-MEYERHOF pathway was confirmed by incorporation of 1-14C-, 3-14C-, and 6-14C-fructose into the spirilloxanthin fraction and analysis of its specific radioactivity.