Chlorobium ferrooxidans

Classification

FIGURE 1. Typical shape and morphology of a bacteria in the genus chlorobium (7).

Domain: Bacteria

Phylum: Chlorobi

Class: Chlorobia

Order: Chlorobiales

Family: Chlorobiaceae

Genus: Chlorobium

Species: ferrooxidans (2)

NCBI link to find]

Species

NCBI: Taxonomy

Chlorobium ferrooxidans

Description and Significance

This green phototrophic bacterium is short, rod-shaped, approximately 0.5x1.0-1.5 μm in size, with rounded ends. The organism is nonmotile, gram negative, and nonsporeforming. Chlorobium ferrooxidans is strictly anaerobic. Originally isolated from shallow freshwater ditches, the phottrophic bacterium (strain KoFox) has only been isolated as a coculture with a strain identified as a member of the ε-subclass of the proteobacteria closely related to Geospirillum arsenophilum (KoFum). When grown in coculture, Chlorobium ferrooxidans oxidizes ferrous iron to ferric iron with stoichiometric formation of cell mass from carbon dioxide. This bacterium is important due to the fact that it is a novel green phototroph, related to other species of Chlorobium yet unique in regards to the oxidation of ferrous iron to ferric iron. This process by bacteria is a relatively novel phenomenon that has only been observed with phototrophic purple sulfur or non-sulfur bacteria (Wkddel et al., 1993; Ehrenreich and Widdel, 1994; Heising and Scchink, 1998). This observation in green phototrophic bacteria may indicate phototrophic ferrous iron oxidation was a widespread metabolic capacity in an early phase of evolution (1).

FIGURE 2. 16s rRNA based tree showing the phylogenetic relationships of C. ferrooxidans (KoFox) and other members of the green sulfur bacteria phylum as well as members of the Cytophaga/Flavobacterium/Bacteroides phylum (1).

Genome Structure

The Chlorobium-like partner (KoFox) in the coculture is genetically related to Chlorobium, Prosthecochloris, and Pelodictyon, however no relationship was found to any strain for which rRNA sequence data currently are available (1). Overall 16S rRNA sequence similarity values of 91.4 - 96.7% indicate that the strain represents a separate line of descent within a Pelodictyon/Prosthechloris cluster (see figure 2). According to the NCBI Genome project website (2), the genome of Chlorobium ferrooxidans is 2.53896 Mbp in length, contains 2158 proteins and 47 RNAs.

FIGURE 3. Photomicrograph of both strains of bacteria living in the co-culture. A. Strain KoFum grown with fumarate. B. The binary mised culture KoFox grown with ferrous carbonate (arrow points at cell of KoFum)(1).

Cell Structure, Metabolism and Life Cycle

The bacterium (KoFox) while living in a coculture with a chemoheterotrophic partner, is presumed to obtain trace nutrients from the Geospirillium-like species. Bacteriochlorophyll c present in the organism makes this bacterium strictly phototrophic with an affinity for dim light excluding light of 740 nm in wavelength. This strian (KoFox) differs from all Chlorobium strains in its lack of sulfide oxidation. Instead KoFox oxidizes ferrous iron to ferric iron hydroxides and use a combination of iron and sunlight to reduce carbon dioxide for making organic compounds. Hydrogen and acetate have been shown to increase the cell yield of the strain KoFox in the presence of ferrous iron. Hydrogen has also been shown to be used as a sole electron source. Oxidation of ferrous iron by KoFox in the presence of KoFum is coupled to biomass formation from Carbon dioxide according to the equation: 17 FeCO3 + 29 H2O --> 17 FE(OH)3 + <C4H7O3> + 13 CO2 (1).

Ecology and Pathogenesis

Habitat; symbiosis; biogeochemical significance; contributions to environment.
If relevant, how does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.

References

(1) Heising, S., Richter, L., Ludwig, W., and Schink, B. 1999. Chlorobium ferrooxidans sp. nov., a phototrophic green sulfur bacterium that oxidizes ferrous iron in coculture with a “Geospirillum” sp. strain. Arch Microbiol. 172:116-124.]

(2) NCBI Genome Project [1]

(3) Widdel, F. Schnell, S., Heising, S., Ehrenreich, A., Assmus, B., Schink, B. 1993. Ferrous iron oxidation by anoxygenic phototrophic bacteria. Nature. 362:834-836.

(4) Ehrenreich, A. and Widdel, F. 1994. Anaerobic oxidation of ferrous iron by purple bacteria, a new type of phototrophic metabolism. Appl. Environ. Microbiol. 60:4517-4526.

(5) Heising S. and Schink, B. 1998. Phototrophic oxidation of ferrous iron by a Rhodmicrobium vannielii strain. Microbiology. 144:2260-2269.

(6) Kappler, A., Pasquero, C., Konhauser, K. O., and Newman, D. K. 2005. Deposition of banded iron formations by anoxygenic phototrophic Fe(II)-oxidizing bacteria. Geology. 33:865-868.

(7) Beatty, J.T.; Overmann, J.; Lince, M.T.; Mansket, A.K.; Lang, A.S.; Blankenship, R.E.; Van Dover, C.L.; Martinson, T.A.; Plumley, F.G. “ An obligately photosynthetic bacterial anaerobe from a deep-sea hydrothermal vent”. PNAS June 28, 2005 vol. 102 no. 26 9306-9310

Author

Page authored by Paul Giordano and Apram Ghuman, students of Prof. Jay Lennon at Michigan State University.