Rhodoferax ferrireducens

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Classification

- Kingdom: Bacteria

- Intermediate Rank 1: Proteobacteria

- Intermediate Rank 2: Betaproteobacteria

- Intermediate Rank 3: Burkholderiales

- Intermediate Rank 4: Comamonadaceae

- Genus: Rhodoferax

- Species: ferrireducens

- Strain: DSM 15236

- Closest relatives are R. fermentans, R. antarticas, and Aquaspirillum delicatum.

- The two other species in the Rhodoferax genus are aerobic organisms while R. ferrireducens is a facultative anaerobe.

- The two other in the Rhodoferax genus are phototrophic organisms while R. ferrireducens is not.

- The two other in the Rhodoferax genus have fermentative growth while there is no fermentative growth detected in R. ferrireducens.

- Although A. delicatum is from a different genus, it is very morphologically very similar to R. ferrireducens.

Description & Significance

- A facultative anaerobe (Most Fe(III) reducing microorganisms are strict anaerobes)

- First time complete oxidation of sugars coupled to Fe(III) reduction has been observed in an organism that grows at a near neutral pH

- Significant because the oxidation of its electron donors has an 83% coulumbic efficiency (compared to 65% from other microorganism that use an insoluble terminal electron acceptor)


Genome Structure

- Circular chromosome that is 4,712,337 bp long.

- Has 4418 different protein genes

- Has 60 different RNA genes

- Has one plasmid pDSM15236 that is 257,447 bp long.

Cell Structure

- 3-5 µm in length, 1 µm in width

- Has one single polar flagellum

- Gram-negative cell during all of its growth phases

- No sporulation detected

- Has membrane bound electron shuttling compounds. Discovered when scientists found that R. ferrireducens biofilm is attached directly to the anode that it is reducing.

Metabolism

- R. ferrireducens can utilize a large host of electron donors.

o Electron donors oxidized: glucose, fructose, sucrose, xylose, lactate, acetate, propinate, pyruvate, malate, succinate, & benzoate. o Electron donors not oxidized: formate, butyrate, ethanol, methanol, glycerol, caproate, isobutyrate, valerate, butanol, propanol, & hydrogen.



- R. ferrireducens can utilize a variety of electron acceptors.

o Electron acceptors reduced: Fe(III)-NTA (Nitrilo triacetic acid), Mn(IV) oxide, fumarate, nitrate,

o Electron acceptors not reduced: poorly crystallized Fe(III) oxide, Fe(III) citrate, anthraquinone-2, 6-disulfonate (AQDS), chromium(VI), cobalt-EDTA, uranium(VI), elemental sulfur, nitrite, selenate or selenite, sulfate, sulfite or thiosulfate


- There was no phototrophic growth detected

- There was also no fermentative growth detected

- Can oxidize glucose to CO-2 with Fe(III) as the sole acceptor.

- Can also convert energy from this type of metabolism to support growth

- Cannot grow on glucose in absence of Fe(III)

- Glucose itself does not react with Fe(III) without the bacteria

- Stoichiometry of bacterial metabolism is consistent with theoretical reaction:

C6H12O6 + 6H2O + 24 Fe(III) fi 6CO2 + 24 Fe(II)  + 24H+

- Growth in carbon rich media produces inclusion bodies that have PHA in them. (PHA presence discovered via Nile Blue staining and UV visualization)

Ecology

- This microorganism was first isolated in the sediments in the waters around Oyster Bay, VA (USA).

- Was first called strain T1 18 by discoverers because it was an isolate from site T1 at a depth of 18 feet.

- Can grow at temperatures as low as 4∞C. It is psychrotolerant, not psychrophilic, so its optimal growth temperature is 25∞C. Other Fe(III) reducing microorganisms cannot grow at temperatures this low.

- Optimal pH is 7.0. Is the first Fe(III) reducing microorganism that grows at a nearly neutral pH.

Pathology

- There is currently no information on the pathological nature of this organism

Applications to biotechnology

- Potential use in microbial fuel cells (MFC) because this organism can not only oxidize carbohydrates, but also other metabolic intermediates such as acetate, lactate, and pyruvate.

- Novel because no additional mediator is required (to shuttle electrons from microorganism to anode). R. ferrireducens can shuttle the electrons to the anode directly and does not need the help of mediators that can often be cytotoxic and can often lower the efficiency of fuel cells.

- Also novel because the layer of R ferrireducens growing on the electrode is responsible for the voltage, not the microbe growing in the solution. This means that the electrode can be shifted to a fresh solution & can grow immediately without needing to filter the solution to keep the organism.


Current Research

- Current research is focused on developing the use of R. ferrireducens as a possible practical microbial fuel cell.

- Some research focuses on discovering other microorganisms like R. ferrireducens with a higher efficiency.

- Other studies focus on trying to figure out which cellular structures are responsible for electron transport across the membrane.


References

Bond, D.R. et al. (2002) “Electrode-reducing microorganisms that harvest energy from marine sediments”. Science 295, 483–485

Chaudhuri, Lovley (2003), “Electricity generation by direct oxidation of glucose in mediatorless microbial fuel cells” Nature Biotechnology 21, 1229-1232

Copeland A. et al. “Complete sequence of chromosome of Rhodoferax ferrireducens DSM 15236.” Submitted (FEB-2006) to the EMBL/GenBank/DDBJ databases.

Copeland A. et al. “Complete sequence of plasmid 1 of Rhodoferax ferrireducens DSM 15236.” Submitted (FEB-2006) to the EMBL/GenBank/DDBJ databases.

Finneran, K.T., Johnsen, C.V., & Lovley, D.R. “Rhodoferax ferrireducens sp. nov., a psychrotolerant, facultatively anaerobic bacterium that oxidizes acetate with the reduction of Fe(III)” Int. J. Sys. Evol. Microbolo. Vol 53, 669-673. (2003).

Palmore, G. Tayhas R. “Bioelectric power generation” TRENDS in Biotechnology. Vol.22 No.3 March 2004

Rabaey, K. Verstraete, W. “Microbial fuel cells: novel biotechnology for energy generation” TRENDS in Biotechnology. Vol.23 No.6 June 2005


KMG