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Wetlands exist near major bodies of water all over the world, and are ecologically comparable in their productivity to rainforests. They are often overlooked as important ecosystems in the earth’s cycles of carbon, nitrogen, and water because they cover relatively little of the planet’s surface. One aspect where wetlands are more productive than rainforests are the microbes in the soil, which thrive on the nutrients that flow throw their habitat as water returns to the ocean. Wetlands are unique environments, as they are high in salts, metals, and organic wastes.

Anaerobic bacteria facilitate many important reactions in nature. By using common ions of iron and sulfur to oxidize organic molecules, metal reducing bacteria break down the products of organic decomposition. As sugars, fats, and proteins are metabolized by microbes, hydrogen ions and electrons are released to the environment. Our fuel cell will use this transfer of electrons to create a current and generate electricity. Anaerobic bacteria thrive in the nutrient-rich, metal-rich environment of wetland ecosystems, which is why our experiment focuses so closely on wetlands soil in the Bay Area.

Below is a quick overview of the genuses of bacteria that research has established as highly electrogenic. These bacteria are found in many ecosystems around the world, including wetlands and aquatic sediment. Many of these bacteria are symbiotically linked, as many species within theses genuses of bacteria produce byproducts during fermentation, which are then metabolized by a different species of bacterium. This leads to the continuous breakdown of organic fuels without loss of energy due to unfermentable waste products.

Organism name	Main fuel oxidized	Waste products of organism	Metal or ion reduced	Additional information
Clostridium Butyricum	Carbohydrates	Lactate, Formate, CO2(gas), H2(gas)	Fe(III)	C. Butyricum is a common fermenting bacteria found in cheese, soil, and the human gut
Shewanella Oneidensis	Lactate, Formate, H2(gas), Acetate	H2S(gas), HS-,	SO42-, S2O32-, SO32-, NO3-, Fe(III), Cr(VI),Mn(IV)	Very versatile bacteria that thrives in many environments. May use H2 gas as electron donor
Aeromonas Hydrophila	Carbohydrates, Acetate, Glycerol	Lactate, Formate	Fe(III), NO3-, SO42-	Aquatic bacteria capable of metabolising many fuels
Geobacter Metallireducens	Fatty acids, Acetate, Aromatic compounds	CO2(gas)	Fe(III)	Useful for bioremediation, breaks down toxic chemicals
Geobacter Sulfurreducens	Fatty acids, Acetate, Aromatic compounds	CO2(gas)	Fe(III)	Useful for bioremediation, breaks down toxic chemicals

Geobacter

Geobacter species generate energy exclusively through anaerobic respiration by reducing various metals and ions. Geobacter metallireducens and Geobacter sulfurreducens have the ability to form conductive bacterial nanowires, which assist in electron transfer during the reaction. By reducing a variety of metals and ions, The Geobacter genus is able to oxidize many organic molecules including aromatics, fatty acids, acetate and possibly petroleum products. By oxidizing waste that other microbes release due to fermentation, Geobacter species are useful for removing metals and decaying organic material in wastewater.

Shewanella

Many species of Shewanella reduce sulfate to sulfides (H2s, HS-), which then oxidizes organic compounds. Some species have the ability to oxidize iron to be used by other microbes, and can use hydrogen gas made by microbes as an electron donor. Shewanella Oneidensis in particular is capable of reducing an array of toxic metals coupled with oxidation of organic molecules. Bacterial nanowires are involved in electron transfer to assist with this. It lives in a variety of environments, such as soil, ocean floors, and sedimentary habitats.

Aeromonas

Species of Aeromonas typically oxidize glucose and pyruvate using Fe(III), and readily oxidize acetate using nitrate. This is produced by nitrogen fixing bacteria on the roots of our cell’s plant. Aeromonas hydrophila is an aquatic bacteria that is found worldwide, and likely to be found in abundance in wetlands.

Clostridium

Clostridium Butyricum is an anaerobe that is commonly sold as a probiotic. Using Iron(III) oxide hydroxide and other minerals containing the Fe(III) ion, many Clostridium species ferments organic molecule to form lactate, formate, butyrate, acetate, carbon dioxide and hydrogen gas. Not all clostridium species/strains are electrogenic however we hope to culture Clostridium. Beijerinckii or C. Butyricum due to their close similarities and high electrochemical activity.

We mention nitrifying bacteria in our video; these most commonly live in colonies on the roots of plants where they provide water soluble nitrates in exchange for sugar. Nitrifying bacteria aren't electrogenic, so they're not included here but we will include more information on them in future lab notes, where we will describe the the relevant symbiotic relationships in more detail. Stay tuned!

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Organism name	Main fuel oxidized	Waste products of organism	Metal or ion reduced	Additional information
Clostridium Butyricum	Carbohydrates	Lactate, Formate, CO2(gas), H2(gas)	Fe(III)	C. Butyricum is a common fermenting bacteria found in cheese, soil, and the human gut
Shewanella Oneidensis	Lactate, Formate, H2(gas), Acetate	H2S(gas), HS-,	SO42-, S2O32-, SO32-, NO3-, Fe(III), Cr(VI),Mn(IV)	Very versatile bacteria that thrives in many environments. May use H2 gas as electron donor
Aeromonas Hydrophila	Carbohydrates, Acetate, Glycerol	Lactate, Formate	Fe(III), NO3-, SO42-	Aquatic bacteria capable of metabolising many fuels
Geobacter Metallireducens	Fatty acids, Acetate, Aromatic compounds	CO2(gas)	Fe(III)	Useful for bioremediation, breaks down toxic chemicals
Geobacter Sulfurreducens	Fatty acids, Acetate, Aromatic compounds	CO2(gas)	Fe(III)	Useful for bioremediation, breaks down toxic chemicals

Geobacter

Shewanella

Aeromonas

Clostridium

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Organism name	Main fuel oxidized	Waste products of organism	Metal or ion reduced	Additional information
Clostridium Butyricum	Carbohydrates	Lactate, Formate, CO2(gas), H2(gas)	Fe(III)	C. Butyricum is a common fermenting bacteria found in cheese, soil, and the human gut
Shewanella Oneidensis	Lactate, Formate, H2(gas), Acetate	H2S(gas), HS-,	SO42-, S2O32-, SO32-, NO3-, Fe(III), Cr(VI),Mn(IV)	Very versatile bacteria that thrives in many environments. May use H2 gas as electron donor
Aeromonas Hydrophila	Carbohydrates, Acetate, Glycerol	Lactate, Formate	Fe(III), NO3-, SO42-	Aquatic bacteria capable of metabolising many fuels
Geobacter Metallireducens	Fatty acids, Acetate, Aromatic compounds	CO2(gas)	Fe(III)	Useful for bioremediation, breaks down toxic chemicals
Geobacter Sulfurreducens	Fatty acids, Acetate, Aromatic compounds	CO2(gas)	Fe(III)	Useful for bioremediation, breaks down toxic chemicals

Geobacter

Shewanella

Aeromonas

Clostridium

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