PHOTOTROPHIC OXIDATION OF FERROUS IRON BY A RHODOMICROBIUM-VANNIELII STRAIN

Oxidation of ferrous iron was studied with the anaerobic phototrophic bacterial strain BS-1. Based on morphology, substrate utilization patt erns, arrangement of intracytoplasmic membranes and the in vivo absorp tion spectrum, this strain was assigned to the known species Rhodomicr obium vannielii. Also, the type strain of this species oxidized ferrou s iron in the light. Phototrophic growth of strain BS-1 with ferrous i ron as electron donor was stimulated by the presence of acetate or suc cinate as cosubstrates. The ferric iron hydroxides produced precipitat ed on the cell surfaces as solid crusts which impeded further iron oxi dation after two to three generations. The complexing agent nitrilotri acetate stimulated iron oxidation but the yield of cell mass did not i ncrease stoichiometrically under these conditions. Other complexing ag ents inhibited cell growth. Ferric iron was not reduced in the dark, a nd manganese salts were neither oxidized nor reduced. It is concluded that ferrous iron oxidation by strain BS-1 is only a side activity of this bacterium that cannot support growth exclusively with this electr on source over prolonged periods of time.