Role of B800–850 Light-Harvesting Pigment-Protein Complex in the Morphogenesis of Rhodobacter sphaeroides Membranes

Abstract

In response to low oxygen tension, the facultative photoheterotrophic bacterium Rhodobacter sphaeroides elaborates an extensive intracytoplasmic membrane (ICM) system, consisting of a series of interconnected vesicles, in which the photosynthetic apparatus is localized (1, 2). In addition to the photochemical reaction center, this structure contains the B875 and B800–850 light-harvesting bacteriochlorophyll a (BChl)-protein complexes which function as core and peripheral antennae, respectively (3). While the core antenna is found in a constant molar ratio to the reaction center of ∼25:1, the amount of B800–850 varies with light intensity (4) and under low illumination, can reach levels more than three-fold greater than those of B875. The ICM is continuous with the cytoplasmic membrane (5, 6, 7), and in vivo surface labeling studies have demonstrated that the interior of the ICM is accessible from the periplasmic space (8, 9).