Studies on a mutant of Rhodopseudomonas spheroides unable to grow photosynthetically

• 1.

  1. Mutants of Rhodopseudomonas spheroides have been isolated that cannot grow photosynthetically but can grow aerobically (in the dark) at the same rate as the parent strain. The major pigments of the photosynthetically dificient mutant PM-8 and its parent strain Ga are bacteriochlorophyll, neurosperene, and hydroxyneurospene. Under conditions of limited aeration both strains contain very similar amounts of these pigments. In chromatophore fractions from these two strains the bacteriochlorophyll shows the same degree of susceptibility to structural and photo-oxidative alterations in the presence of detergents.

• 2.

  2. A blue-green mutant strain, PM-8:bg58, derived from strain PM-8, suffers photooxidative injury sensitized by bacteriochlorophyll in the same way as do photosynthetically competent blue-green (colored carotenoid-less) strains such as uv-33.

• 3.

  3. Strain PM-8 exhibits none of the reversible light-induced absorbancy changes detectable in strain Ga. These changes, some of which have been implicated in the primary photochemistry of photosynthesis, reflect oxidation of cytochromes, oxidation of P870 (a specialized, minor bacteriochlorophyll component), reduction of ubiquinone, and a shift in the absorption bands of carotenoids. A chemically induced difference spectrum characteristics of the oxidation of P870 is also lacking in strain PM-8.

• 4.

  4. Strain PM-8 does not show a light-induced electron-spin-resonance signal, whereas photosynthetically competent strains of purple bacteria do.

• 5.

  5. The yield of bacteriochlorophyll fluorescence in strain PM-8 is about two times that in strai Ga. A transient increase in flourescence intensity correlated with bleaching of P870 was observed in strain Ga but not in strain PM-8.

• 6.

  6. It is concluded that in strain PM-8 the photochemical reaction centers that initiate the chemistry of photosynthesis are absent or inoperative.