Pigment composition in heterotrophically and photoheterotrophically grown rhodopseudomonas capsulata

Abstract

The main purpose of this research was to investigate the pigment composition of and localisation within the photosynthetic bacterium Rhodopseudomonas capsulata grown aerobically heterotrophically, anaerobically photoheterotrophically and during transference bflween these two states.
Nine carotenoids were isolated from anaerobically lightgrown Rps. cczpsutata and seven of these from aerobically dark-grown cells. The relative amounts were different.
After a typical transfer, anaerobiosis was rapidly achieved but there was a 50 minute lag before the onset of RITA synthesis, and there was no growth for 20 hours. Pigment changes observed, thus occurred while the cells were not growing. Bchl concentrations began to increase soon after the transition but the carotenoid concentration decreased during the first hour, before increasing. The three main carotenoids present in dark aerobic cultures behaved differently following the transfer.
Chromatophores were present in aerobic dark-grown cells of Rps. ccrosulata and a method was developed to isolate the active reaction centre complexes and light-harvesting complexes also present.
The carotenoids present in both complexes qualitatively mirrored the whole cell carotenoid content and were ordered as shown by Circular Dichroisn. Three typical polypeptides were isolated from the reaction centre complexes and four from the light-harvesting preparations, these being a mixture of the two light-harvesting complexes.
After a typical transition the carotenoid concentration of lightharvesting complexes increased, although whole cell concentrations decreased, suggesting the possible movement of carotenoid molecules into the light-harvesting complexes. Reaction centre carotenoid concentrations decreased. Bchl concentrations in all complexes increased after one hour. The Bchl of reaction centre complexes and/or light-harvesting complex I were synthesized first. The maximum concentration of the Bchl of light-harvesting complex II was 5 hours after the transition.
Chromatophores isolated from cells transferred from dark to light, after 30 minutes illumination, showed an increased carotenoid shift whether cells maintained aerobically or anaerobically. This development was apparently triggered by light alone, and no consistent alteration in carotenoid concentration under the different conditions was found to correlate with it.