The effect of growth conditions on the light-harvesting apparatus in Rhodopseudomonas acidophila.

The detailed effect on the light-harvesting apparatus of three different wild-type strains of Rhodopseudomonas acidophila in response to changes in both light-intensity and temperature have been investigated. In all three strains at high light-intensities (160 μmol s m(2) and above) the only LH2 antenna complex synthesised is the B800-850 complex. In strains 7050 and 7750 as the light-intensity is lowered the B800-850 complex is gradually replaced by another type of LH2 the B800-820 complex. However, at no light-intensities studied is this changeover complete when the cells are grown at 30°C. If however, the light-intensity is lowered at temperatures below 25°C with strain 7750 there is a complete replacement of the B800-850 complex by the B800-820 complex. At all light-intensities and temperatures tested, strain 10050 only synthesised the B800-850 complex. Strain 7050 also responded to changes in light-intensity by altering its carotenoid composition. At high light-intensity the major carotenoids were rhodopin and rhodopin-glucoside, while at low light-intensities the major ones were rhodopinal and rhodopinal-glucoside. This change in carotenoid content started to occur at rather higher light-intensities than the switchover from B800-850 to B800-820.