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Topic Name: University of Minnesota Researchers have Confirmed that Riboflavin be Key for Converting Waste to Electricity

Category: Organic electronics

Research persons: Daniel Bond, Jeffrey Gralnick

Location: University of Minnesota, United States

Details

Researchers at the University of Minnesota studying bacteria capable of generating electricity have discovered that riboflavin (commonly known as vitamin B-2) is responsible for much of the energy produced by these organisms.

The bacteria, Shewanella, are commonly found in water and soil and are of interest because they can convert simple organic compounds (such as lactic acid) into electricity, according to Daniel Bond and Jeffrey Gralnick, of the University of Minnesota's BioTechnology Institute and department of microbiology, who led the research effort.

"This is very exciting because it solves a fundamental biological puzzle," Bond said. "Scientists have known for years that Shewanella produce electricity. Now we know how they do it."

The discovery means Shewanella can produce more power simply by increased riboflavin levels. Also, the finding opens up multiple possibilities for innovations in renewable energy and environmental clean-up. The research is published in the March 3 issue of the Proceedings of the National Academy of Sciences.

The interdisciplinary research team, which included several students, showed that bacteria growing on electrodes naturally produced riboflavin. Because riboflavin was able to carry electrons from the living cells to the electrodes, rates of electricity production increased by 370 percent as riboflavin accumulated.

Scaled-up "microbial fuel cells" using similar bacteria could generate enough electricity to clean up wastewater or power remote sensors on the ocean floor. "Bacteria could help pay the bills for a wastewater treatment plant," Bond said. But more ambitious applications, such as electricity for transportation, homes or businesses, will require significant advances in biology and in the cost-effectiveness of fuel cell materials. Why do these bacteria produce electricity? In nature, bacteria such as Shewanella need to access and dissolve metals such as iron. Having the ability to direct electrons to metals allows them to change their chemistry and availability.

"Bacteria have been changing the chemistry of the environment for billions of years," said Gralnick. "Their ability to make iron soluble is key to metal cycling in the environment and essential to most life on earth."

Note for Riboflavin
Riboflavin (E101), also known as vitamin B2, is an easily absorbed micronutrient with a key role in maintaining health in animals. It is the central component of the cofactors FAD and FMN, and is therefore required by all flavoproteins. As such, vitamin B2 is required for a wide variety of cellular processes. Like the other B vitamins, it plays a key role in energy metabolism, and is required for the metabolism of fats, carbohydrates, and proteins.
Milk, cheese, leafy green vegetables, liver, legumes such as mature soybeans, yeast and almonds are good sources of vitamin B2, but exposure to light destroys riboflavin.
Riboflavin is not toxic when taken orally, as its low solubility keeps it from being absorbed in dangerous amounts from the gut. Although toxic doses can be administered by injection, any excess at nutritionally relevant doses is excreted in the urine, imparting a bright yellow color when in large quantities.
Various biotechnological processes have been developed for industrial scale riboflavin biosynthesis using different microorganisms, including filamentous fungi such as Ashbya gossypii, Candida famata and Candida flaveri as well as the bacteria Corynebacterium ammoniagenes and Bacillus subtilis. The latter organism has been genetically modified to both increase the bacteria's production of riboflavin and to introduce an antibiotic (ampicillin) resistance marker, and is now successfully employed at a commercial scale to produce riboflavin for feed and food fortification purposes. The chemical company BASF has installed a plant in South Korea, which is specialized on riboflavin production using Ashbya gossypii. The concentrations of riboflavin in their modified strain are so high, that the mycelium has a reddish / brownish color and accumulates riboflavin crystals in the vacuoles, which will eventually burst the mycelium.
Riboflavin is yellow or yellow-orange in color and in addition to being used as a food coloring it is also used to fortify some foods. It is used in baby foods, breakfast cereals, pastas, sauces, processed cheese, fruit drinks, vitamin-enriched milk products, some energy drinks, and is widely used in vitamin supplements.
Large quantities of riboflavin are often included in multi-vitamins; often, the dose is far more than a normal human can use in a day. The excess is excreted in the urine, causing the urine to be colored bright yellow within a few hours of ingestion of the vitamin.
It is difficult to incorporate riboflavin into many liquid products because it has poor solubility in water. Hence the requirement for riboflavin-5'-phosphate (E101a), a more expensive but more soluble form of riboflavin.

Note for Lactic Acid
Lactic acid also known as milk acid, is a chemical compound that plays a role in several biochemical processes. It was first isolated in 1780 by a Swedish chemist, Carl Wilhelm Scheele, and is a carboxylic acid with a chemical formula of C3H6O3. It has a hydroxyl group adjacent to the carboxyl group, making it an alpha hydroxy acid (AHA). In solution, it can lose a proton from the acidic group, producing the lactate ion CH3CH(OH)COO−. It is miscible with water or ethanol, and is hygroscopic.
Lactic acid is chiral and has two optical isomers. One is known as L-(+)-lactic acid or (S)-lactic acid and the other, its mirror image, is D-(-)-lactic acid or (R)-lactic acid. L-(+)-Lactic acid is the biologically important isomer.
In animals, L-lactate is constantly produced from pyruvate via the enzyme lactate dehydrogenase (LDH) in a process of fermentation during normal metabolism and exercise. It does not increase in concentration until the rate of lactate production exceeds the rate of lactate removal which is governed by a number of factors including: monocarboxylate transporters, concentration and isoform of LDH and oxidative capacity of tissues. The concentration of blood lactate is usually 1-2 mmol/L at rest, but can rise to over 20 mmol/L during intense exertion.
Industrially, lactic acid fermentation is performed by Lactobacillus bacteria, among others. These bacteria can operate in the mouth; the acid they produce is responsible for the tooth decay known as caries.
In medicine, lactate is one of the main components of Ringer's lactate or lactated Ringer's solution (Compound Sodium Lactate or Hartmann's Solution in the UK). This intravenous fluid consists of sodium and potassium cations, with lactate and chloride anions, in solution with distilled water in concentration so as to be isotonic compared to human blood. It is most commonly used for fluid resuscitation after blood loss due to trauma, surgery or a burn injury.
Two molecules of lactic acid can be dehydrated to lactide, a cyclic lactone. A variety of catalysts can polymerise lactide to either heterotactic or syndiotactic polylactide, which as biodegradable polyesters with valuable (inter alia) medical properties are currently attracting much attention.
Nowadays, lactic acid is used as a monomer for producing polylactic acid (PLA) which later has application as biodegradable plastic. This kind of plastic is a good option for substituting conventional plastic produced from petroleum oil because of low emission of carbon dioxide that can contribute to global warming. The commonly used process in producing lactic acid is via fermentation, and later to obtain the polylactic acid, the polymerization process follows.
Lactic acid is widely used for inhibiting pathogenic bacteria like E.coli, Salmonella, Campylobacter and Listeria on animal carcasses like beef, pork and poultry during the slaughtering process.
Potassium lactate, sodium lactate and calcium lactate are the neutralized salts of lactic acid. Potassium lactate is used in many fresh and cooked meat products for shelf life control, color preservation and reduction of sodium content. Sodium lactate has a mild saline taste and is therefore suitable for flavour enhancement in meat products as well. Sodium lactate is being produced as liquids as well as powders. Calcium lactate is popular for fortification and improved texture in emulsified meat products like frankfurters.

Note for Microbial Fuel Cell
A microbial fuel cell (MFC) or biological fuel cell is a bio-electrochemical system that drives a current by mimicking bacterial interactions found in nature. Micro-organisms catabolize compounds such as glucose (Chen et al., 2001), acetate, butyrate (Liu et al., 2005) or wastewater (Habermann & Pommer, 1991). The electrons gained from this oxidation are transferred to an anode, where they depart through an electrical circuit before reaching the cathode. Here they are transferred to a high potential electron acceptor such as oxygen. As current now flows over a potential difference, power is generated directly from biofuel by the catalytic activity of bacteria.
A microbial fuel cell is a device that converts chemical energy to electrical energy by the catalytic reaction of microorganisms (Allen and Bennetto, 1993). A typical microbial fuel cell consists of anode and cathode compartments separated by a cation specific membrane. In the anode compartment, fuel is oxidized by microorganisms, generating electrons and protons. Electrons are transferred to the cathode compartment through an external electric circuit, and the protons are transferred to the cathode compartment through the membrane. Electrons and protons are consumed in the cathode compartment, combining with oxygen to form water. In general, there are two types of microbial fuel cells, mediator and mediator-less microbial fuel cells. Biological fuel cells take glucose and methanol from food scraps and convert it into hydrogen and food for the bacteria.
Most of the microbial cells are electrochemically inactive. The electron transfer from microbial cells to the electrode is facilitated by mediators such as thionine, methyl viologen, methyl blue, humic acid, neutral red and so on (Delaney et al., 1984; Lithgow et al., 1986). Most of the mediators available are expensive and toxic.
Microbial fuel cells have a number of potential uses. The first and most obvious is harvesting the electricity produced for a power source. Virtually any organic material could be used to ‘feed’ the fuel cell. MFCs could be installed to waste water treatment plants. The bacteria would consume waste material from the water and produce supplementary power for the plant. The gains to be made from doing this are that MFCs are a very clean and efficient method of energy production. A fuel cell’s emissions are well below regulations (Choi, et al., 2000). MFCs also use energy much more efficiently than standard combustion engines which are limited by the Carnot Cycle. In theory an MFC is capable of energy efficiency far beyond 50% (Yue & Lowther, 1986).
However MFCs do not have to be used on a large scale, as the electrodes in some cases need only be 7 μm thick by 2 cm long (Chen, et al., 2001). The advantages to using an MFC in this situation as opposed to a normal battery is that it uses a renewable form of energy and would not need to be recharged like a standard battery would. In addition to this they could operate well in mild conditions, 20°C to 40°C and also at pH of around 7 (Bullen, et al., 2005). Although more powerful than metal catalysts, they are currently too unstable for long term medical applications such as in pacemakers (Biotech/Life Sciences Portal).

The process could be reversed to prevent corrosion of iron and other metals on ships. Bond and Gralnick were each recently awarded funding from the U.S. Navy to explore this and other potential applications.

This research was funded by the Initiative for Renewable Energy and the Environment, the National Science Foundation, the National Institutes of Health and Cargill.

The university's BioTechnology Institute is co-sponsored by the College of Biological Sciences and the Institute of Technology.

In figure, Vitamin B2 (riboflavin) crystals