Studies in carotenogenesis. 9. General cultural conditions controlling carotenoid (spirilloxanthin) synthesis in the photosynthetic bacterium Rhodospirillum rubrum

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Abstract
The dry wt. of cultures of R. rubrum can be determined by measuring the extinction of the suspension at 1[mu]. wavelength. Spirilloxanthin, together with traces of its cis isomers, is the only carotenoid synthesized by R. rubrum. Phytofluene, zeta-carotene, neurosporene or related polyenes were not present. On a malate-glutamate-salt medium max. growth occurred when cultures were 4-6 days old. Mean max. dry wt. production by both strains C and D was 75, 10 and 125 mg./100 ml. for light-aerobic, dark-aerobic and anaerobic (light) cultures, respectively. The rate of spirilloxanthin synthesis is lower in young cultures than in old, reaching its max. about 4 days after inoculation. Mean max. concns. in strain C were 1.8, 1.1 and 3.5 mg./g. (dry wt.) for light-aerobic, dark-aerobic, and anaerobic cultures, respectively. Diphenylamine up to a concn. of 7.15 [mu]g./ml. (1/40,000) inhibits synthesis of spirilloxanthin and bacteriochlorophyll without affecting growth. Adenosine-5-phosphate and riboflavin had no counteracting effect on diphenylamine inhibition. In both aerobic and anaerobic cultures streptomycin at 100-1000 [mu]g./ml. almost completely inhibits growth.