THE PHOTOSYNTHETIC APPARATUS OF RHODOSPIRILLUM MOLISCHIANUM

Abstract

By varying thc light intensity and tcmpcrature during growth it is possible to obtain cultures of Rhodospirillum molischianum in which the spccific bacteriochlorophyll contents differ by as much as fivcfold. We used such cultures to compare the changes in the electron microscopic appearance of the cells with thc changes in thc amount and bacteriochlorophyll content of chromatophorc matcrial isolated from cell extracts. Thc cells contained a variable number of internal membranes which arc invaginations of the cell mcmbrane. The shape, size, number, and arrangement of the infoldings varied as the specific bacteriochlorophyll content of the cells changed. In cells with little bactcriochlorophyll, the invaginations were mostly tubular. In cells with largcr amounts of bacteriochlorophyll, the invaginations were disc-shaped and the discs were apprcsscd togcther in stacks of 2 to 10 discs each. Variations in the number of discs per stack could bc accounted for by a simplc statistical model. The average area pcr disc increased with increasing bactcriochlorophyll content. Quantitative estimations of the relative volumcs occupicd by mcmbranes in cells with four different bacteriochlorophyll contents showed that thc amount of internal membranc alone had no direct relationship with the bacteriochlorophyll content of the cells; however, the total amount of membrane (cell membrane plus internal membrane) was directly proportional to the bactcriochlorophyll content. The specific bacteriochlorophyll content of isolated chromatophore material was proportional to the bacteriochlorophyll contcnt of whole cells; the total amount of chromatophore material was independent of the bactcriochlorophyll content of whole cells. Several possible explanations of this paradoxical discrepancy between the electron microscope obscrvations and the analytical results are discussed.

Antenna mixing in photosynthetic membranes from Phaeospirillum molischianum

“…However, Fig. 1A is in agreement with the spectra observed by Gibbs et al (19). This shift of absorption is associated with a modification in the LH2 polypeptides synthesized through differential expression of the various puc operons.…”

“…In many species of bacteria, adaptation to low light intensities involves changing the proportions of core complexes and LH2. Extra LH2 are synthesized to increase the effective reaction center absorption cross section (18,19). This modification is associated with the formation of large para-crystalline domains of LH2 in the photosynthetic membranes (20).…”

Ectothiorhodospira halochloris sp. nov., a new extremely halophilic phototrophic bacterium containing bacteriochlorophyll b

“…Intracytoplasmic membranes occur as stacks (Figs. 2 and 3) as in the brown colored Rhodospirillum species, R.fulvum, R. molischianum, R.photometricum (Gibbs et al, 1965) and the species of the genus Ectothiorhodospira, E. shaposhnikovii (Cherni et al, 1969), E. mobilis (Trfiper, 1968;Remsen et al, 1968;Holt et al, 1968) and E.…”

Fine structure of an unusual photosynthetic bacterium

“…Such observations have led Holt, Conti, and Fuller (1966b) to conclude that the formation of the photosynthetic apparatus is an inverse function of light intensity which correlates with the proposal by Cohen-Bazire and Kunisawa (1963), that the amount of pigment in cells of R. rubrum is inversely related to light intensity and oxygen tension. Gibbs, Sistrom, and Worden (1965) showed that a paradox existed between elec tron microscopic observations and analytical results regarding the amount of bacteriochlorophyll and chromatophore material in the cell.…”

“…The several mechanisms that have been proposed to account for the origin of chromatophores can be summarized as follows: (1) formation of a reticulum by infoldings of the cytoplasmic membrane into the cytoplasm as observed in Rhodo spirillum rubrum (Cohen-Bazire and Runisawa, 1963); (2) direct forma tion by invagination of the cytoplasmic membrane from which discrete, uniform vesicles are formed in: R. rubrum (Cohen-Bazire and Kunisawa, 1963;Boatman, 1964;Oda and Horio, 1964); and in Rhodopseudomonas spheroides (Gibson, 1965); (3) by binary fission as indicated by the "dumb-bell" shaped chromatophores of R. spheroides (Gibson, 1965); and (4) fragmentation of the intracytoplasmic membranes as in Rhodospirillum rubrum (Hickman and Frenkel, 1965b;Holt and Marr, 1965b). The photosynthetic apparatus is described as a lamellar array rather than a vesicular system in Rhodospirillum molischianum (Drews, 1960;Giesbrecht and Drews, 1962;Hickman and Frenkel, 1965a;Gibbs, Sistrom, and Worden, 1965); Rhodomicrobium vannielli (Boatman and Douglas, 1961;Vatter, Douglas, and Wolfe, 1959); and Rhodopseudomonas viridis (Drews and Giesbrecht, 1965;1966).…”