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- Bacteria- Chlorobi- Chlorobia- Chlorobiales- Chlorobiaceae- Chlorobium/Pelodictyon group- Chlorobium- Chlorobium ferrooxidans (2)
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, this bacterium 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". 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 (Heising et al. 1999).
Describe the size and content of the genome. How many chromosomes? Circular or linear? Other interesting features? What is known about its sequence? The Chlorobium-like partner in the coculture KoFox 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 Chlorobium/Pelodictyon/Prosthechloris cluster (see figure 2). According to the NCBI Genome project website (2), Chlorobium ferrooxidans genome is 2.53896 Mbp in length, contains 2158 proteins and 47 RNAs.
Cell Structure, Metabolism and Life Cycle
Interesting features of cell structure; how it gains energy; what important molecules it produces. 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 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. Hydrogen is also used as a sole electron source. Oxidation of ferrous iron by KoFox in the presence of KoFum is coupled to biomass formation from CO2 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.
(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 
(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.
Page authored by Paul Giordano and Apram Ghuman, students of Prof. Jay Lennon at Michigan State University.