Photosynthetic conversion of formate and CO2 to glutamate by rhodopseudomonas palustris

Isolation and growth rates of methanol utilizing Rhodospirillaceae

38 pure culture strains belonging to seven species of the Rhodospirillaceae were isolated from 39 methanol enrichment cultures inoculated with water and mud samples of different habitats. None of the strains exhibited doubling times shorter than 10 h in methanol-bicarbonate media.

Utilization of methanol by rhodospirillaceae

Enrichment culture of organisms growing anaerobically in the light in methanol-bicarbonate medium resulted in isolation of strains of Rhodopseudomonas gelatinosa and Rhodopseudomonas acidophila. The pH optimum for growth on methanol for all strains tested was approximately one unit higher than for growth on carbon sources containing more than one carbon atom. At the appropriate pH, 17 strains of Rhodospirillaceae out of 39 in a culture collection grew anaerobically in the light on methanol-bicarbonate. Rhodopseudomonas acidophia strain 10050 showed the most abundant growth and was studied in more detail. Its growth on methanol was stimulated by yeast extract or vitamin-free casamino acids. The organism grew on methanol-bicarbonate, methanol-formate or formate alone as the sole carbon sources. No growth was observed on methylamine or fomaldehyde. In the presence of excess bicarbonate a maximum yield of 98 g cell material from 100 g methanol was obtained. Ribulose diphosphate carboxylase was present in the methanol-bicarbonate-grown organism at six times the specific activity of that in the succinate-grown organism.

Reductive pentose cycle and formate assimilation in Rhodopseudomonas palustris

Rhodopseudomonas palustris assimilated formate autotrophically as carbon dioxide and hydrogen arising from the activity of the formic hydrogenlyase system. Kinetic analyses of cell suspensions pulse-labeled with (14)C-formate or (14)C-bicarbonate showed similar distributions of incorporated radioactivity. In both cases phosphate esters were the first assimilation products. Ribulose diphosphate carboxylase, phosphoribose isomerase, and phosphoribulokinase, characteristic enzymes of the reductive pentose cycle, were present in extracts of cells grown on formate.

Formic hydrogenlyase and the photoassimilation of formate by a strain of Rhodopseudomonas palustris

A photosynthetic bacterium isolated by enrichment on media containing formate as major source of cell carbon was identified as a strain of Rhodopseudomonas palustris. It grew on a wide range of simple organic compounds including alcohols, fatty acids, and hydroxyacids, on a chemically defined medium with biotin and p-aminobenzoic acid as essential growth factors. The organism grew on formate or photoautotrophically with molecular hydrogen or thiosulfate only in the presence of yeast extract. Ability to photoassimilate formate could be shown only in organisms grown in the presence of formate. The organism contained an inducible formic hydrogenlyase consisting of a soluble formic dehydrogenase, a particulate hydrogenase, and one or more intermediate, but as yet unidentified, electron carriers. The formic hydrogenlyase could be reconstituted from a particulate hydrogenase and a partially purified soluble formic dehydrogenase. Some properties of the formic dehydrogenase and hydrogenase have been compared with that of the formic hydrogenlyase system.