By Catherine Brahic

Geobacter – a current favourite

STICK an electrode in the ground, pump electrons down it, and they will come: living cells that eat electricity. We have known bacteria to survive on a variety of energy sources, but none as weird as this. Think of Frankenstein’s monster, brought to life by galvanic energy, except these “electric bacteria” are very real and are popping up all over the place.

Unlike any other living thing on Earth, electric bacteria use energy in its purest form – naked electricity in the shape of electrons harvested from rocks and metals. We already knew about two types, Shewanella and Geobacter. Now, biologists are showing that they can entice many more out of rocks and marine mud by tempting them with a bit of electrical juice. Experiments growing bacteria on battery electrodes demonstrate that these novel, mind-boggling forms of life are essentially eating and excreting electricity.

That should not come as a complete surprise, says Kenneth Nealson at the University of Southern California, Los Angeles. We know that life, when you boil it right down, is a flow of electrons: “You eat sugars that have excess electrons, and you breathe in oxygen that willingly takes them.” Our cells break down the sugars, and the electrons flow through them in a complex set of chemical reactions until they are passed on to electron-hungry oxygen.

“Life’s clever. It figures out how to suck electrons out of everything we eat and keep them under control”

In the process, cells make ATP, a molecule that acts as an energy storage unit for almost all living things. Moving electrons around is a key part of making ATP. “Life’s very clever,” says Nealson. “It figures out how to suck electrons out of everything we eat and keep them under control.” In most living things, the body packages the electrons up into molecules that can safely carry them through the cells until they are dumped on to oxygen.

“That’s the way we make all our energy and it’s the same for every organism on this planet,” says Nealson. “Electrons must flow in order for energy to be gained. This is why when someone suffocates another person they are dead within minutes. You have stopped the supply of oxygen, so the electrons can no longer flow.”

Video: Electric bacteria connect to form wires

The discovery of electric bacteria shows that some very basic forms of life can do away with sugary middlemen and handle the energy in its purest form – electrons, harvested from the surface of minerals. “It is truly foreign, you know,” says Nealson. “In a sense, alien.”

Nealson’s team is one of a handful that is now growing these bacteria directly on electrodes, keeping them alive with electricity and nothing else – neither sugars nor any other kind of nutrient. The highly dangerous equivalent in humans, he says, would be for us to power up by shoving our fingers in a DC electrical socket.

To grow these bacteria, the team collects sediment from the seabed, brings it back to the lab, and inserts electrodes into it.

First they measure the natural voltage across the sediment, before applying a slightly different one. A slightly higher voltage offers an excess of electrons; a slightly lower voltage means the electrode will readily accept electrons from anything willing to pass them off. Bugs in the sediments can either “eat” electrons from the higher voltage, or “breathe” electrons on to the lower-voltage electrode, generating a current. That current is picked up by the researchers as a signal of the type of life they have captured.

“Basically, the idea is to take sediment, stick electrodes inside and then ask ‘OK, who likes this?’,” says Nealson.

Shocking breath

At the Goldschmidt geoscience conference in Sacramento, California, last month, Shiue-lin Li of Nealson’s labpresented results of experiments growing electricity breathers in sediment collected from Santa Catalina harbour in California. Yamini Jangir, also from the University of Southern California, presented separate experiments which grew electricity breathers collected from a well in Death Valley in the Mojave Desert in California.

Over at the University of Minnesota in St Paul, Daniel Bond and his colleagues have published experiments showing that they could grow a type of bacteria that harvested electrons from an iron electrode (mBio, doi.org/tqg). That research, says Jangir’s supervisor Moh El-Naggar, may be the most convincing example we have so far of electricity eaters grown on a supply of electrons with no added food.

But Nealson says there is much more to come. His PhD student Annette Rowe has identified up to eight different kinds of bacteria that consume electricity. Those results are being submitted for publication.

Nealson is particularly excited that Rowe has found so many types of electric bacteria, all very different to one another, and none of them anything like Shewanella or Geobacter. “This is huge. What it means is that there’s a whole part of the microbial world that we don’t know about.”

“This is huge. What it means is there’s a whole part of the microbial world that we don’t know about”

Discovering this hidden biosphere is precisely why Jangir and El-Naggar want to cultivate electric bacteria. “We’re using electrodes to mimic their interactions,” says El-Naggar. “Culturing the ‘unculturables’, if you will.” The researchers plan to install a battery inside a gold mine in South Dakota to see what they can find living down there.

NASA is also interested in things that live deep underground because such organisms often survive on very little energy and they may suggest modes of life in other parts of the solar system.

Electric bacteria could have practical uses here on Earth, however, such as creating biomachines that do useful things like clean up sewage or contaminated groundwater while drawing their own power from their surroundings. Nealson calls them self-powered useful devices, or SPUDs.

Practicality aside, another exciting prospect is to use electric bacteria to probe fundamental questions about life, such as what is the bare minimum of energy needed to maintain life.

For that we need the next stage of experiments, says Yuri Gorby, a microbiologist at the Rensselaer Polytechnic Institute in Troy, New York: bacteria should be grown not on a single electrode but between two. These bacteria would effectively eat electrons from one electrode, use them as a source of energy, and discard them on to the other electrode.

Gorby believes bacterial cells that both eat and breathe electrons will soon be discovered. “An electric bacterium grown between two electrodes could maintain itself virtually forever,” says Gorby. “If nothing is going to eat it or destroy it then, theoretically, we should be able to maintain that organism indefinitely.”

It may also be possible to vary the voltage applied to the electrodes, putting the energetic squeeze on cells to the point at which they are just doing the absolute minimum to stay alive. In this state, the cells may not be able to reproduce or grow, but they would still be able to run repairs on cell machinery. “For them, the work that energy does would be maintaining life – maintaining viability,” says Gorby.

How much juice do you need to keep a living electric bacterium going? Answer that question, and you’ve answered one of the most fundamental existential questions there is.

Leader: “Spark of life revisited thanks to electric bacteria”

Wire in the mud

Electric bacteria come in all shapes and sizes. A few years ago, biologists discovered that some produce hair-like filaments that act as wires, ferrying electrons back and forth between the cells and their wider environment. They dubbed them microbial nanowires.

Lars Peter Nielsen and his colleagues at Aarhus University in Denmark have found that tens of thousands of electric bacteria can join together to form daisy chains that carry electrons over several centimetres – a huge distance for a bacterium only 3 or 4 micrometres long. It means that bacteria living in, say, seabed mud where no oxygen penetrates, can access oxygen dissolved in the seawater simply by holding hands with their friends.

Such bacteria are showing up everywhere we look, says Nielsen. One way to find out if you’re in the presence of these electron munchers is to put clumps of dirt in a shallow dish full of water, and gently swirl it. The dirt should fall apart. If it doesn’t, it’s likely that cables made of bacteria are holding it together.

Nielsen can spot the glimmer of the cables when he pulls soil apart and holds it up to sunlight (see video).

Flexible biocables

It’s more than just a bit of fun. Early work shows that such cables conduct electricity about as well as the wires that connect your toaster to the mains. That could open up interesting research avenues involving flexible, lab-grown biocables.

This article appeared in print under the headline “The electricity eaters”

{ https://www.newscientist.com/ }

Closing in on Jupiter: 7 Fun Facts About Juno's Mission — **Artist's illustration of NASA's Juno spacecraft arriving at Jupiter on July 4, 2016.**
**Credit: NASA**

NASA's Juno spacecraft will reach Jupiter Monday (July 4) after a five-year journey through deep space. The probe will study the structure and evolution of the solar system's largest planet from orbit, taking measurements for more than a year despite Jupiter's intense radiation environment.

"Jupiter is the planet on steroids in our solar system; everything about it is extreme," Juno principal investigator Scott Bolton, of the Southwest Research Institute in San Antonio, told Space.com.

The mission has several major science goals. One is to learn how much water is inside Jupiter, which should yield insights about the amounts of water that were present in the solar system's early days. [Juno's Jupiter Arrival: Complete Coverage]

Juno scientists also hope to map out Jupiter's interior, determining (among other things) whether or not the planet has a rocky core. Such information should help researchers learn more about the planet-formation process in general, shedding light on the nature of worlds throughout the Milky Way galaxy, mission team members have said.

"It's a big challenge," Bolton said, "but we have to take those challenges if we're going to explore and learn about ourselves, and how we fit into nature."

Here are seven things to know about Juno's mission:

1. Jupiter's radiation will take a toll on Juno

Juno is scheduled to orbit Jupiter for about 20 months. The spacecraft likely can't keep going much longer than that, because of the intense radiation environment at Jupiter.

For example, the planet's magnetic field is about 20,000 times as intense as Earth's, so Juno will have to withstand impacts by many charged particles moving at superfast speeds. [Juno's Jupiter Mission Fraught with Danger (Video)]

That's not to say that NASA isn't doing its best to keep the probe safe. Juno harbors a radiation-shielded electronics vault, the first of its kind. The vault is a cube about the size of an SUV's trunk, made of titanium about 0.3 inches (0.8 centimeters) thick. Inside are some of the most precious parts of Juno — its brain (command and data-handling box), its power and distribution unit, and 20 other key electronics components, according to a NASA press kit. With instruments inside, the vault has a mass of about 500 lbs. (200 kilograms).

2. Juno only has about as much hard-drive space as your laptop

The spacecraft's main computer has about as much memory as a laptop with a solid-state drive. The computer features 256 megabytes of flash memory — to preserve data even in the event of a power interruption — and 128 megabytes of dynamic random-access memory (DRAM). DRAM is useful in situations where low cost and high capacity are required at the same time, NASA officials have said.

Why not give Juno more memory? The spacecraft uses the BAE Systems RAD750 single-board computer, which is designed for high-radiation environments. This computer has been used many times in space, including for NASA missions such as the Van Allen probes (which fly through Earth's radiation belts), the Mars Reconnaissance Orbiter and the Mars rover Curiosity.

Juno: Inside NASA's mission to Jupiter

https://youtu.be/Z1jkNC8IR1Y

3. Juno is the most distant solar-powered spacecraft ever

Juno has gone farther into deep space than any other solar-powered probe. The spacecraft set the record in January, when it was about 493 million miles (793 million kilometers) from the sun, surpassing the distance of the European Space Agency's Rosetta spacecraft during the latter's journey to Comet 67P/Churyumov-Gerasimenko.

Most spacecraft that venture so far from the sun need to use nuclear power to keep going. But Juno is able to generate enough power, thanks to its three huge solar panels, each of which is 30 feet (9 meters) long. These arrays will generate about 500 watts of power at Jupiter, mission team members have said.

4. Juno will spin while doing science

Juno spins to stay stable, a strategy that borrows from the design of NASA's old Pioneer probes. Two Pioneer spacecraft (Pioneers 10 and 11) sailed by Jupiter in 1973 and are still cruising out into the solar system, albeit silently; NASA lost contact with Pioneer 10 in 2003 and Pioneer 11 in 1995.

Juno's spin rate has varied quite a bit during its journey so far. When its main engine fires, Juno spins up to 5 revolutions per minute (RPM). During cruise periods, this rate dips to 1 RPM.

When doing science operations, however, Juno will spin at 2 RPM. At this rate, Juno's field of view will move across Jupiter 400 times during one journey from pole to pole. The spacecraft will not use a "scan platform" to point its instruments because of the spinning design, and also because the instruments don't need to point in different directions at the same time.

Juno mission: British rocket engine ready for Jupiter task | Short News

https://youtu.be/N7KluwTxUV8

5. Juno will take nearly three months to reach its final orbit

After Juno inserts itself into Jupiter's orbit, the probe will spend 107 days in what is called a "capture orbit." Scientists chose to take this long way around instead of inserting Juno directly into its final, 14-day orbit, because the direct route would have required a lot of fuel.

The capture orbit not only saves fuel, but it also gives mission scientists a chance to check out their instruments and begin science observations from afar. According to NASA, the team will begin using all the instruments to collect data about 50 hours after Juno is inserted into Jupiter's orbit.

6. Juno has an unusual final orbit

The best way to map any world is to move a spacecraft repeatedly over the poles. Then the entire world can spin beneath the probe, allowing it to map every part of the surface. But at Jupiter, there's a rub — high levels of potentially damaging radiation close to the planet.

As a way to minimize its radiation exposure, Juno will fly in a very elongated orbit. At the south end of its orbit, Juno will be at its closest approach to Jupiter: just 3,100 miles (5,000 kilometers). But as it leaves the south polar region, Juno will fly way out beyond the moon Callisto's orbit, which lies about 1.2 million miles (1.9 million km) from Jupiter.

This highly elliptical orbit will also keep Juno's solar panels in sunlight, NASA officials have said.

NASA's Juno Mission: Everything You Could Want to Know

https://youtu.be/_fI0IrwTMbg

7. Juno will die a dramatic death

In the past few decades, scientists have learned that life is incredibly hardy and persistent. Earth microbes thrive in boiling-hot, deep-sea vents at the bottom of the ocean, and some can even survive exposure to the harsh environment of space.

It's therefore possible that some Earth organisms may still be alive aboard Juno. Scientists and NASA officials don't want to take the chance that such microbes could contaminate Jupiter's ocean-harboring moon Europa — one of the solar system's best bets to host alien life — or other Jovian satellites such as Ganymede or Callisto.

So at the end of its mission, Juno will perform a 5.5-day maneuver that will crash it into Jupiter's atmosphere intentionally. The mission is scheduled to end in February 2018, but it may be extended slightly.

Follow Elizabeth Howell @howellspace, or Space.com @Spacedotcom. We're also on Facebook and Google+. Original article on Space.com.