The very fast cyt c photooxidation observed after flash excitation in E. ursincola, S. sibiricus, R. thiosulfatophilus, and R. denitrificans (, , ) confirmed that the immediate electron donor to the RC in these species is a cyt c tightly bound to the RC. The difference spectrum measured at 50 μs was centered at 556 nm and correlates with the wavelength position of high-potential hemes of RC-bound cyts c of various photosynthetic bacteria (Fig. A) (, , , ). The wavelength of maximum bleaching at 5 ms was centered at 551 nm and corresponds to the photooxidation of soluble cyt c species, as reported for whole cells of the anaerobic phototrophic bacterium R. viridis (). A large bleaching of cyt c attributed to photooxidation of soluble cyt c was induced in aerobic phototrophic bacterial species under continuous illumination ().
A second possibility is that lateral transfer of photosynthesis genes (, , ) might have resulted in the acquisition of a photosynthesis gene cluster by nonphotosynthetic aerobes. However, the relatively recent acquisition of multigene-dependent photosynthetic complexes by lateral gene transfer to yield all aerobic phototrophic bacteria seems to be less likely.
The dominant groups are purple sulfur bacteria, ..
The RC of anaerobic phototrophic bacteria is thought to be surrounded by a ring-shaped LHI complex at a fixed stoichiometry relative to the RC (). A constant number of about 30 LHI Bchl molecules per RC has been measured for seven aerobic phototrophic species (). These results are in good accordance with data reported for anaerobic phototrophic bacteria (, , ) and suggest a similar overall organization of the photosynthetic apparatus in aerobic and anaerobic phototrophic bacteria. Nevertheless, the LH complexes of some aerobic phototrophic bacteria have unusual spectral properties presumably due to different protein environments of the Bchl (see “Light-harvesting systems”).
What Is Photosynthesis? From Light Energy to Chemical …
All species of aerobic phototrophic bacteria synthesize large amounts of carotenoid pigments, which determine the color of the organism and give peaks in the blue and green regions (420 to 550 nm) of absorption spectra (Fig. ) (, , , , –, –). The carotenoid composition is species specific, often indicating a large number of different carotenoids of unusual chemical structure (–, ).
Light-dependent reactions - Wikipedia
The only carotenoid of Acidiphilium rubrum is spirilloxanthin, which is found in Rhodospirillum rubrum and several other purple phototrophic bacteria ().
Diversity of Microbial Metabolism
The strains 15s.b. and 23s.b., recently discovered at English Bay, Vancouver, Canada (), and Porphyrobacter tepidarius () are the only nonmotile aerobic phototrophic bacteria. The strains 15s.b. and 23s.b. form ovoid cells (0.4 to 0.6 by 1.2 to 1.5 μm) surrounded by capsules and frequently produce a matrix in which cells are embedded (Fig. ). Therefore, these strains are nonmotile and highly agreggative in liquid culture ().
Adriano Reis Lucheta I; Marcio Rodrigues Lambais II
Typically, cells of aerobic phototrophic bacteria contain small amounts of Bchl relative to the abundance of carotenoids (compared to anaerobic purple phototrophic bacteria). For example, the anaerobic phototrophic bacterium R. sphaeroides may yield about 20 nmol of Bchl/mg (dry weight) of cells, whereas the Bchl content of obligately aerobic species was found to be as follows: E. longus, 2.0 nmol/mg (dry weight) of cells; S. sibiricus and E. hydrolyticum, 1.0 to 4.0 nmol/mg of protein; A. rubrum, 0.7 nmol/mg (dry weight) of cells; R. thiosulfatophilus, 0.1 to 1.0 nmol/mg of protein. Therefore, the ratio of Bchl to carotenoid peaks in whole cells of aerobic phototrophic species is typically about 1:8 to 1:10 (, , , , , , , , ). (However, see “The influence of light on growth and pigment formation” and “Effect of oxygen on growth and pigment synthesis” for a discussion of oxygen and light effects on Bchl content of cells.)