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

Abstract

A green phototrophic bacterium was enriched with ferrous iron as sole electron donor and was isolated in defined coculture with a spirilloid chemoheterotrophic bacterium. The coculture oxidized ferrous iron to ferric iron with stoichiometric formation of cell mass from carbon dioxide. Sulfide, thiosulfate, or elemental sulfur was not used as electron donor in the light. Hydrogen or acetate in the presence of ferrous iron increased the cell yield of the phototrophic partner, and hydrogen could also be used as sole electron 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 as photosynthetic pigments, and also resembled representatives of this species morphologically. On the basis of 16S rRNA sequence comparisons, this organism clusters with Chlorobium, Prosthecochloris, and Pelodictyon species within the green sulfur bacteria phylum. Since the phototrophic partner in the coculture KoFox is only moderately related to the other members of the cluster, it is proposed as a new species, Chlorobium ferrooxidans. The chemoheterotrophic 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 sequence comparison. The "Geospirillum" strain was present in the coculture only in low numbers. It fermented fumarate, aspartate, malate, or pyruvate to acetate, succinate, and carbon dioxide, and could reduce nitrate to dinitrogen gas. It was not involved in ferrous iron oxidation but possibly provided a thus far unidentified growth factor to the phototrophic partner.

Iron formations: A global record of Neoarchaean to Palaeoproterozoic environmental history

“…A different biological model was proposed by Garrels et al (1973) and Hartman (1984) Widdel et al, 1993;Heising et al, 1999;Straub et al, 1999). The ferric iron minerals these strains produce are also consistent with the most likely precursor IF minerals, Fe(III)-oxyhydroxides (Kappler and Newman, 2004).…”

Fossilized iron bacteria reveal a pathway to the biological origin of banded iron formation

“…Three major mechanisms are currently implicated in the oxidation of Fe 2 þ to Fe 3 þ : abiotic O 2 precipitation 1,26 , UVdriven photochemical Fe 2 þ oxidation 1,2 and microbial transformation 1,3,[6][7][8][9][10][11][12][13][14]28 . In addition to the low Archaean O 2 levels, recent experimental studies have rejected photochemical Fe 2 þ oxidation as a potential major contributor to BIF formation 1,3 .…”

“…Instead, biotic, anoxygenic photoferrotrophic precipitation according to the equation 4Fe 2 þ þ CO 2 þ 11H 2 O þ light-[CH 2 O] þ 4Fe(OH) 3 þ 8H þ has been proposed [6][7][8][9][10][11][12][13][14] . With the exemption of proxies such as iron isotopes 12,13 , there exists no direct environmental evidence-neither in ancient nor in modern ecosystems-demonstrating how photoferrotrophs could have accounted for vast-scale biological BIF deposition, including the formation of their spectacular banded consistency.…”

Early anaerobic metabolisms

“…In any event, a dynamic and interesting ecosystem could have resulted, driven by iron-oxidizing phototrophs oxidizing Fe 2C dissolved in the oceans (figure 6). As far as we know, this was first envisioned by Garrels & Perry (1974), and this idea has been considerably strengthened by the discovery of bacteria capable of oxidizing Fe 2C phototrophically ( Widdel et al 1993;Heising et al 1999;Jiao et al 2005). Indeed, the link has been made between phototrophic iron oxidation and the deposition of Archaean and Early Proterozoic BIFs (Hartman 1984;Eherenreich & Widdel 1994a,b;Kappler et al 2005).…”