http://www.sciencedaily.com/releases/2013/10/131008102549.htm

Bacterial cells use an impressive range of strategies to grow, develop and sustain themselves. Despite their tiny size, these specialized machines interact with one another in intricate ways.

In new research conducted at Arizona State University's Biodesign Institute, Jonathan Badalamenti, César Torres and Rosa Krajmalnik-Brown explore the relationships of two important bacterial forms, demonstrating their ability to produce electricity by coordinating their metabolic activities.

In a pair of papers recently appearing in the journal Biotechnology and Bioengineering, the group demonstrates that the light-sensitive green sulfur bacterium Chlorobium can act in tandem with Geobacter, an anode respiring bacterium. The result is a light-responsive form of electricity generation.

"Geobacter is not light responsive in its own right because it's not a photosynthetic organism," says Badalamenti, lead author of the two new papers. In contrast, photosynthetic Chlorobium is unable to carry out the anode form of respiration necessary for electricity production. "But when you put these two organisms together, you get both a light response and the ability to generate current."

The electrons Geobacter acquires from its photosynthetic partner Chlorobium can be measured and collected in the form of electricity, using a device known as a microbial fuel cell (MFC) -- a kind of biological battery.

Microbial fuel cells may one day generate clean electricity from various streams of organic waste, simply by exploiting the electron-transfer abilities of various microorganisms.

The research was carried out at the Swette Center for Environmental Biotechnology, which is under the direction of Regents' Professor Bruce Rittmann. The goal of the Center is to exploit microorganisms for the benefit of society. These efforts typically involve the use of bacteria to clean up environmental pollutants or to provide clean energy. In the case of MFC research, bacteria can assist in both of these activities, generating useable electricity from energy-rich waste.

In the new studies, the researchers explore the possibility of enhancing electricity production in MFCs by examining the function of light-responsive

Chlorobium, a photosynthetic green sulfur bacterium. The resulting experimental configuration, in which light responsive bacteria play a role in energy generation, is known as a microbial photoelectrochemical cell (MPC).

To explore the behavior of photosynthetic bacteria in a MPC, the team first used a clever means of selectively enriching phototrophs such as Clorobium in a mixed culture, by poising the device's anode at a particular electrical potential that was favorable for phototrophic growth, yet unfavorably low for the growth of non-photosynthetic anode respiring bacteria.

The researchers then noted an intriguing result: electricity production measured at the anode was linked to phases when the MPC was in total darkness and dropped during periods when the bacterial culture was exposed to light.

The group detected the presence of Chlorobium in the enrichment cultures using pyrosequencing and reasoned that the observed negative light responsiveness was either due to photosynthetic Chlorobium directly transferring electrons to the anode during dark phases or instead, transferring these electrons to a non-photosynthetic anode respiring bacterium like Geobacter, through an intermediary reaction.

Phototrophic organisms like Chlorobium are not known to carry out direct anode respiration. As Krajmalnik-Brown explains: "The follow up sceintific question was to disern if we had discovered a novel phototrophic anode respiring bacteria or if the phototroph was giving something to the anode respiring bacteria Geobacter and that was the response we were reporting."

In subsequent experiments, pure cultures of either Chlorobium or anode-respiring Geobacter were examined as well as co-cultures combining the two. In the case of Chlorobium alone, light responsive electricity generation was not observed. Similarly, pure Geobacter cultures failed to produce electrical current when deprived of an electron donor like acetate in the medium.

Only when the photosynthetic Chlorobium were combined with anode respiring Geobacter in co-culture experiments did electricity generation occur and it did so in a negative light-responsive manner -- increasing in periods of darkness and falling off during light phases.

The experimental results of the co-culture study suggest the following scenario: Chlorobium bacteria gather energy from light in order to fix carbon dioxide and fuel their metabolism. During dark phases however, they sustain themselves by switching from photosynthesis to dark fermentation, using energy they have stored. Acetate is produced as a metabolic byproduct of this dark phase fermentation.

During periods of darkness, anode respiring Geobacter gains electrons from the acetate produced through Chlorobium metabolism, transferring them to the MPC anode, thereby producing the observed rise in electrical current. "In this second study, we deliberately removed any sources of electrons that were present in the growth medium," Badalamenti says. When the two bacterial communities were forced to interact, it was clear that Chlorobium was helping to provide food for the Geobacter, in a light-responsive manner.

The authors note that one of the attractive advantages of their study is that electricity generation measured at the anode can be used as a highly accurate surrogate for the complexities of bacterial metabolism taking place in the MPC culture. "Unlike having to measure metabolites or cell growth either microscopically or through chemical intermediates, we are able to construct a co-culture system in which one of the readouts is electricity," Badalamenti says. "We can then monitor metabolism in the system in real time."

Further questions concerned whether the presence of Chlorobium may provide benefits for Geobacter in naturally occurring cultures, not confined to MFC devices. In anode-free experiments the group showed that the very survival of Geobacter in the absence of alternative sources of electrons was contingent on the presence of Chlorobium-derived acetate.

In addition to establishing a mechanism for light-responsive electricity generation in MFCs, the research points to the power of similar co-culture studies for elucidating a range of energy-producing microbial interactions.

Story Source:

The above post is reprinted from materials provided by Arizona State University. The original item was written by Richard Harth. Note: Materials may be edited for content and length.

Journal References:

1. Jonathan P. Badalamenti, César I. Torres, Rosa Krajmalnik-Brown.Coupling dark metabolism to electricity generation using photosynthetic cocultures. Biotechnology and Bioengineering, 2013; DOI: 10.1002/bit.25011

2. Jonathan P. Badalamenti, César I. Torres, Rosa Krajmalnik-Brown.Light-responsive current generation by phototrophically enriched anode biofilms dominated by green sulfur bacteria. Biotechnology and Bioengineering, 2013; 110 (4): 1020 DOI: 10.1002/bit.24779

Bacteria can be Source of Electricity, Researchers Develop Prototype

http://www.hngn.com/articles/23177/20140129/bacteria-can-be-source-of-electricity-researchers-develop-prototype.htmh

Prototype of an electric generator which uses bacteria to generate electricity.

The prototype is powered by alternating the humidity of the environment

between the humidity levels of a misty day and that of a sunny day to cause

the sheet of latex rubber, which is covered with spores, to straighten and

bend. The generator will work by using the movement of the sheet of

rubber. The back and forth bending of the sheet of rubber coated with

spores on one side can be used to generate electricity.

"If this technology is developed fully, it has a very promising endgame," said Ozgur Sahin, Ph.D., lead author of the study and an associate professor from Columbia University, in a press release.Sahin and his colleagues studied a soil bacterium called Bacillus subtilis which wrinkles as it dries out much like a grape wrinkling to form a raisin. However, unlike grapes which cannot reform into raisins, the

bacterium will be able to assume their original shape after they have access to moisture.They discovered that changing the humidity is enough to initiate the movement of the spores, and a spore-coated plank can generate as much as 1000 times force as the human muscle. Sahin has to experiment with other materials for the actuator but he concluded that rubber is more promising than silicon and plastic."Solar and wind energy fluctuate dramatically when the sun doesn't shine or the wind doesn't blow, and we have no good way of storing enough of it to supply the grid for long," said Don Ingber, M.D., Ph.D, Director of Wyss Institute Founding. "If changes in humidity could be harnessed to generate electricity night and day using a scaled up version of this new generator, it could provide the world with a desperately needed new source of renewable energy."

How Do Bacteria Produce Power in a Microbial Fuel Cell? *

http://www.sciencebuddies.org/science-fair-projects/project_ideas/MicroBio_p032.shtml

Topsoil is packed with bacteria that generate electricity when placed in a microbial fuel cell (MFC). Because such bacteria-laden soil is found almost everywhere on Earth, microbial fuel cells can make clean, renewable electricity nearly anyplace around the globe. As natural resources are being depleted, scientists' attention has shifted to pursuing alternative energy sources, such as MFCs, even more than before.

A microbial fuel cell, also known as a biological fuel cell, is a device that can use microbes to generate electricity. An MFC has two electrodes and an area that separates the electrodes (called a membrane). For an MFC to function, electricity must flow into one electrode and leave the other electrode. How is this accomplished? It has to do with the bacteria in the MFC. Some types of soil bacteria can help generate electricity. These bacteria, known as electrogenic bacteria, include the Shewanella species, which can be found in almost any soil on Earth and are shown in Figure 1, and the Geobacter species, which prefer living in soil deep underground or even under the ocean, where no oxygen is present. The soil bacteria eat

what is in the soil, such as microscopic nutrients and sugars, and in turn, produce electrons that are released back into the soil. Electrons are subatomic particles that have a negative charge. These electrons can be harnessed and used to create electricity, which is a form of energy.

 Figure 1. This is a high-magnification image of Shewanella bacteria, specifically the species S. oneidensis. The bacteria are the cylindrical-

shaped rods scattered in this image. (The other parts of the image are ice pieces that the bacteria were submerged in to take this picture.) (Image

credit: PLoS Biology)

In an MFC using these soil bacteria, one electrode (specifically the anode) is buried down in damp soil. Down there, the bacteria multiply and cover the electrode (creating a biofilm on it), supplying it with a lot of electrons. At the same time, the other electrode (called the cathode) is placed on the top of the soil, leaving one of its sides completely exposed to the air. Electrons from the bottom electrode travel up a wire to the top electrode and, once there, they react with oxygen (from the air) and hydrogen (made by the bacteria as it digests nutrients in the soil) to create water.

What do you think happens to the quantity of bacteria in the MFC as the power output increases? Does the number of bacteria, increase, decrease, or stay relatively stable? One way to investigate this would be to take a swab of the soil at the beginning of the experiment and grow the bacteria from the swab, and then take a swab when the power output is much greater and grow the bacteria from that swab. Do you see more bacteria growing on the nutrient agar plate from the second swab taken? Do you see different types of microbes growing? To learn how to set up the microbial fuel cell and take power output measurements, see Science

Buddies' science project ideas Turn Mud into Energy with a Microbial Fuel Cell — and a Dash of Salt and Powered by Pee: Using Urine in a Microbial Fuel Cell. For an idea of how to take bacterial swabs and grow them on agar plates, see Science Buddies' science project idea Is That Really Bacteria Living in My Yogurt? (Note: Shewanella bacteria can be aerobic [they need oxygen] or anaerobic [they grow without oxygen], and Geobacter bacteria are anaerobic. Knowing this, why do you think an anaerobic chamber might be ideal for doing this experiment?).

Bacterial hair-like extensions appear to be capable of conducting electricity down their length, possibly playing a key role in respiration by allowing the cells to dump electrons at distances far outside the cell.

The results, reported online today (11th October) in Proceedings of the National Academy of Sciences, add to a controversial body of literature about the function of these conductive pili, or "nanowires." "It is the first time in which [researchers] actually measure electron transport along the wires at micrometer distances, [which] make it a biologically relevant process," said microbiologist Gemma Reguera   of Michigan State University, who was not involved in the research. "This suggests they could be relevant mode of respiration for bacteria."

"It's an incredibly important finding," agreed microbiologist Derek Lovley of the University of Massachusetts, who also did not participate in the study. "It's fascinating that these microorganisms can make electricity and can get electrons outside the cell."

Shewanella oneidensis MR-1 are among a class of bacteria that can generate energy using solids, such as metal oxides, as electron acceptors. Unlike oxygen, for example, which diffuses into cells to accept the electrons produced during respiration, these solids are found outside cells. These bacteria must thus find a way to transport their electrons to solid surfaces across the cell membrane. A number of strategies have been proposed for how bacteria can accomplish this. If the cells are in direct contact with the solids, electron transfer proteins on the cell membrane can transfer the electrons. Alternatively, small soluble molecules may act as chauffeurs, shuttling the electrons to their final destination.

Shewanella oneidensis strain MR-1 

Image: Wikimedia commons,Gross L, PLoS Biology Vol.

4/8/2006, e282

Recently, a third mechanism of electron dumping has been proposed: Bacteria use nanowires to conduct the electrons to areas where the metal electron acceptors may be more abundant. Evidence that nanowires actually conduct electrons, or electricity, down their length has been lacking, however. To resolve this lingering question, biophysicist Moh El-Naggar of the University of Southern California and his colleagues grew S. oneidensis under conditions that promote the production of lots of nanowires, namely by limiting the number of available electron acceptors. They then rested platinum rods at each end of a nanowire and applied a voltage. Sure enough, the nanowire conducted the current. When the nanowires were snipped, the current stopped.

"It's the first demonstration that these bacterial nanowires are actually conductive," El-Naggar said. "The question is now, what are the implications for these bacterial nanowires in entire microbial communities?"

Until in vivo measurements can be made, it is impossible to know if the bacteria are using the nanowires as a mechanism for transporting electrons for respiration, El-Naggar cautioned. Unfortunately, the techniques available today are adopted from research on inorganic wires, which may impact any findings, he said. But when the group repeated the experiment using a different technique, they got the same results. "Our research indicates that bacteria produce nanowires that are capable of mediating electron transport over long distances."

The team also repeated the experiment using mutant bacteria that lacked two electron transfer proteins known as cytochromes, suspected to be important for conducting electricity. These mutants did not conduct a current. If it turns out these bacteria are indeed linking up into complex biological circuits, "the implications are huge," El-Naggar said. "If [the nanowires are] central to the functioning and to the survival of the community, it enables us to either try to optimize it or even disrupt it."

In the case of microbial fuel cells, for example, which produce electricity by oxidizing biofuels, understanding how these nanowires work could allow researchers to increase the efficiency of the process. Conversely, in the case of pathogenic biofilms, it could provide a target to try to disrupt bacterial function.

Another potential application of these nanowires is in bioremediation of toxic heavy metals, said chemical engineer Plamen Atanassov   of the University of New Mexico, who was not involved in the research. "The hope is that bacteria like Shewanella with its ability to reduce metal oxides will be successfully deployed as a bioremediation agent."

But more research is needed before these applications are realized, said Reguera. "We first have to do these baby steps of characterizing the

physical and biology properties of the wires themselves," she said, such as what they are made of. "And perhaps, once they know that, they may be able to mass produce them and explore applications in nanotechnology."

Microbial fuel cells generate electricity from "metal-breathing"

bacteria in ordinary mud.

http://makezine.com/projects/make-30/bacteria-battery/

Microorganisms often get a bad name because some of them cause disease. But many have useful abilities, from making beer, cheese, and wine to processing waste and cleaning up toxic chemicals. One type of bacteria, discovered in 1987 by Derek Lovley, can generate electricity. Here’s how you can find bacteria like these in a local pond and put them to work.

Most non-photosynthesizing bacteria, like all animals, get their energy from the cellular respiration process, which converts glucose and oxygen to water and carbon dioxide. Oxygen works as an oxidizer, which means it accepts electrons as it combines with other chemicals in reactions. But special bacteria underground have no oxygen to breathe. Instead, they produce energy for their growth by transferring electrons to clumps of rust and other surrounding metal oxides, in a process called dissimilatory metal reduction. We now know that these electric bacteria are found in mud virtually everywhere on Earth, as well as in soil and compost heaps.

A microbial fuel cell (MFC) does the same thing as a battery: drive electrons from an anode to a cathode through chemical oxidation/reduction reactions. What makes MFCs different is that they run on organic substrate and bacteria.

“Metal-breathing” (Geobacter) bacteria at the anode carry out the oxidation reaction, converting plant and animal debris in the mud into electricity and

carbon dioxide. Electrons flow through wires to a cathode sitting in water above the mud, where they combine with oxygen to complete the circuit. The bacteria are highly efficient in this arrangement and can produce electricity continuously for many months or even years.

Experimental MFC-powered buoys now operate in the Potomac River, using naturally occurring bacteria in the mud to measure and transmit meteorological data.

These “Benthic Unattended Generators” (BUGs) have worked for several years with no decrease in power output (see http://nrl.navy.mil/code6900/bug). Geobacter species possess other useful abilities, such as the ability to respire radioactive uranium and remove it from ground water. They have proven versatile and effective in cleaning up areas contaminated with uranium or organic pollutants.

In addition to their scientific interest, MFCs are a useful educational tool: a popular science project that encompasses microbiology, chemistry, electronics, and other disciplines. That’s why Keego Technologies developed the MudWatt, a low-cost microbial fuel cell kit. They also support online discussion forums for MFC makers.

With the MudWatt, students of all ages are learning about MFCs and making scientifically relevant discoveries. For example, a 6th-grade student in Santa Cruz uncovered (literally) a river sediment that produces twice as much power as typical topsoil.