DEVELOPMENT OF PHOTOSYNTHETIC APPARATUS IN DARK CULTURES OF RHODOPSEUDOMONAS CAPSULATA

The influence of the oxygen partial pressure on the morphogenesis of thylakoids, the biosynthesis of bacteriochlorophyll, and the activity of photophosphorylation is investigated. 1. The growth rate (doubling time of protein) in aerobically grown dark cultures of Rhodopseudomonas capsulata is in a relative wide range independent of the oxygen partial pressure. The protein doubling time in a complex medium at 30° C amounts to 2.5-2.75 hrs in the range of 4-100 mm Hg (pO2). On conditions that the pO2 is saturated (150-160 mm Hg) the growth will be reduced about 10%. Underneath a critical oxygen partial pressure (4 mm Hg) the oxydative metabolism and the growth rate are strongly limited. 2. The rate of bacteriochlorophyll synthesis in the log phase of aerobic dark cultures is strongly related to the oxygen partial pressure. The production of bacteriochlorophyll comes to a maximum in the range of 3 to 5 mm Hg (pO2). But bacteriochlorophyll is produced up to 60-70 mm Hg (pO2). The rate of bacteriochlorophyll synthesis is relatively high below 20 mm Hg. 3. The production rate of bacteriochlorophyll is greatly enhanced when the oxygen partial pressure is suddenly lowered. Therefore the specific bacteriochlorophyll content of the cells (μg BChl./mg Protein) is strongly increased until a characteristic new level has been attained after 8 hrs. 4. The regulation of the bacteriochlorophyll synthesis in relation to the oxygen partial pressure in the medium is between 4 to 100 mm Hg (pO2) during log phase growth independent of the growth rate. 5. The biosynthesis of the photochemical apparatus (measured as photophosphorylating activity) of Rhodopseudomonas capsulata is increased likewise by lowering of the oxygen partial pressure. But the kinetic is different from that of bacteriochlorophyll synthesis. The increase in activity of light induced phosphorylation (PP) is enhanced lineary to the protein content of the membrane fraction. But the PP/bacteriochlorophyll ratio is decreased after a short increase. The bacteriochlorophyll content of the intracellular membranes is increased from 3.3 to 33.9 μg/mg protein two hours after induction (pO2: 160 mm Hg→5 mm Hg). 6. Micrographs of thin sections show intracellular membrane structures in high aerated (pO2 150-160 mm Hg) as well as in low aerated cultures (pO2 5 mm Hg). In aerobic cultures tubular membrane structures and in semiarobic cultures vesicular thylakoids (chromatophores) are to be seen. 7. The results demonstrate clearly that the production rate of the bulk of bacteriochlorophyll is not strictly paralled with the biosynthesis of the photochemical apparatus and the membrane morphogenesis. © 1969 Springer-Verlag.