Chlorobium ferrooxidans sp nov., a phototrophic green sulfur bacterium that oxidizes ferrous iron in coculture with a "Geospirillum" sp strain

A green phototrophic bacterium was enriched with ferrous iron as sole elect ron donor and was isolated in defined coculture with a spirilloid chemohete rotrophic bacterium. The coculture oxidized ferrous iron to ferric iron wit h stoichiometric formation of cell mass from carbon dioxide. Sulfide, thios ulfate, or elemental sulfur was not used as electron donor in the light. Hy drogen or acetate in the presence of ferrous iron increased the cell yield of the phototrophic partner, and hydrogen could also be used as sole electr on source. Complexed ferric iron was slowly reduced to ferrous iron in the dark, with hydrogen as electron source. Similar to Chlorobium limicola, the phototrophic bacterium contained bacteriochlorophyll c and chlorobactene a s photosynthetic pigments, and also resembled representatives of this speci es morphologically. On the basis of 16S rRNA sequence comparisons, this org anism clusters with Chlorobium, Prosthecochloris, and Pelodictyon species w ithin the green sulfur bacteria phylum. Since the phototrophic partner in t he coculture KoFox is only moderately related to the other members of the c luster, it is proposed as a new species, Chlorobium ferrooxidans. The chemo heterotrophic partner bacterium, strain KoFum, was isolated in pure culture with fumarate as sole substrate. The strain was identified as a member of the epsilon-subclass of the Proteobacteria closely related to "Geospirillum arsenophilum" on the basis of physiological properties and 16S rRNA sequen ce comparison. The "Geospirillum" strain was present in the coculture only in low numbers. It fermented fumarate, aspartate. malate, or pyruvate to ac etate, succinate, and carbon dioxide, and could reduce nitrate to dinitroge n gas. It was not involved in ferrous iron oxidation but possibly provided a thus far unidentified growth factor to the phototrophic partner.