The bay at the Danish port of Aarhus is pretty enough, with the usual fare of beach-goers, holiday homes and yachts. But the bay’s most spectacular residents live in the mud beneath its water. Back in 2010, Lars Peter Nielsen found that this mud courses with electric currents that extend over centimetres. Nielsen suspected that the currents were carried by bacteria that behaved like electric grids. Two years on, it seems he was right. But what he found goes well beyond what even he had imagined.
Nielsen’s student Christian Pfeffer has discovered that the electric mud is teeming with a new type of bacteria, which align themselves into living electrical cables. Each cell is just a millionth of a metre long, but together, they can stretch for centimetres. They even look a bit like the cables in our electronics—long and thin, with an internal bundle of conducting fibres surrounded by an insulating sheath.
Nielsen thinks that each cable can be considered as a single individual, composed of many cells. “To me, it’s obvious that they are multicellular bacteria,” he says. “This was a real surprise. It wasn’t among any of our hypotheses. These distances are a couple of centimetres long—we didn’t imagine there would be one organism spanning the whole gap.”
The bacteria are members of a family called Desulfobulbaceae, but their genes are less than 92 percent identical to any of the group’s known members. “They’re so different that they should probably be considered a new genus,” says Nielsen. They’re only found in oxygen-starved mud, but where they exist, there’s a lot of them. On average, Pfeffer found 40 million cells in a cubic centimetre of sediment, enough to make around 117 metres of living cable.
Your skin is teeming with bacteria. There are billions of them, living on the dry parched landscapes of your forearms, and the wet, humid forests of your nose. On your feet alone, every square centimetre has around half a million bacteria. These microbes are more than just passengers, hitching a ride on your bodies. They also affect how you smell.
Skin bacteria are our own natural perfumers. They convert chemicals on our skin into those that can easily rise into the air, and different species produce different scents. Without these microbes, we wouldn’t be able to smell each other’s sweat at all. But we’re not the only ones who can sniff these bacterial chemicals. Mosquitoes can too. Niels Verhulst from Wageningen University and Research Centre has just found that the bacteria on our skin can affect our odds of being bitten by a malarial mosquito.
On April 20, 2010, a bubble of methane raced up the drill column of the Deepwater Horizon oil rig, bursting through the seals and barriers in its way. By the time it exploded on the platform’s surface, it had grown to 164 times its original size. The rig, severed by the explosion, caught fire and sank two days later, allowing oil and gas to spew into the Gulf of Mexico for 83 long days.
This chaotic methane bubble was just a vanguard. With the well unsealed, substantial amounts of the gas were released into the gulf. This plume of dissolved methane should have lurked in the water for years, hanging around like a massive planetary fart. But by August, it had disappeared. On three separate trips through the gulf, John Kessler from Texas A&M University couldn’t find any traces of the gas above background levels. He thinks he knows why – the methane was eaten by bacteria.
Note: Serious concerns have been raised about the conclusions of this study. I’ve written a summary of the backlash in a separate post.
Arsenic isn’t exactly something you want to eat. It has a deserved reputation as a powerful poison. It has been used as a murder weapon and it contaminates the drinking water of millions of people. It’s about as antagonistic to life as a chemical can get. But in California’s Mono Lake, Felisa Wolfe-Simon has discovered bacteria that not only shrug off arsenic’s toxic effects, but positively thrive on it. They can even incorporate the poisonous element into their proteins and DNA, using it in place of phosphorus.
Out of the hundred-plus elements in existence, life is mostly made up of just six: carbon, hydrogen, oxygen, nitrogen, sulphur and phosphorus. This elite clique is meant to be irreplaceable. But the Mono Lake bacteria may have broken their dependence on one of the group – phosphorus – by swapping it for arsenic. If that’s right, they would be the only known living things to do this.
Imagine taking a course of antibiotics and suddenly finding that your sexual preferences have changed. Individuals who you once found attractive no longer have that special allure. That may sound far-fetched, but some fruit flies at Tel Aviv University have just gone through that very experience. They’re part of some fascinating experiments by Gil Sharon, who has shown that the bacteria inside the flies’ guts can actually shape their sexual choices.
The guts of all kinds of animals, from flies to humans, are laden with bacteria and other microscopic passengers. This ‘microbiome’ acts as a hidden organ. It includes trillions of genes that outnumber those of their hosts by hundreds of times. They affect our health, influencing the risk of obesity and chronic diseases. They affect our digestion, by breaking down chemicals in our food that we wouldn’t normally be able to process. And, at least in flies, they can alter sexual preferences, perhaps even contributing to the rise of new species.
The natural world is full of great partnerships. Bacteria give animals the guts to digest all manner of otherwise inedible foods. Algae allow corals to harness the power of the sun and construct mighty reefs. Ants cooperate to become mighty superorganisms. But the greatest partnership of all is far more ancient. It’s so old that we can only infer that it took place by looking for signals of history, embedded into the genomes of modern species. The details of how and when it happened are still the source of fierce debate but this was undoubtedly the most important merger in the history of life on Earth: a partnership between two simple cells that would underlie the rise of every living animal, plant, fungus and alga.
Humans are capable of great charity, taking hits to their bank accounts and bodies to benefit their peers. But such acts of altruism aren’t limited to us; they can be found in the simple colonies of bacteria too.
Bacteria are famed for their ability to adapt to our toughest antibiotics. But resistance doesn’t spring up evenly across an entire colony. A new study suggests that a small cadre of hero bacteria are responsible for saving their peers. By shouldering the burden of resistance at a personal cost, these charitable cells ensure that the entire colony survives.
If you’re trapped in a building, it’s probably not the best time to start setting fire to things. But this is exactly what some bacteria do when they find themselves in a human; they cause diseases that are potentially fatal but not contagious. Without an escape, they risk going down with their host. This seems like a ludicrous strategy but we’re looking at it from the wrong perspective – our own. In truth, humans often have nothing to do with the diseases that plague us; we’re just collateral damage in an invisible war.
Like all living things, bacteria have to defend themselves against predators like amoebas. Some species do so using resistance genes that turn them from passive victims into aggressive fighters. And by coincidence, these same adaptations make them more virulent (good at causing disease) in human bodies. We’re just caught in the crossfire.
Animals must wage a never-ending war against parasites, constantly evolving new ways of resisting these threats. Resistance comes in many forms, including genes that allow their owners to shrug off infections. But one species of fly has developed a far more radical solution – it has formed a partnership with a bacterium that lives in its body and defends it against a parasitic worm. So successful is this microscopic bodyguard that it’s spreading like wildfire across America’s besieged flies.
The fly Drosophila neotestacea is plagued by a nematode worm called Howardula. Around a quarter of adults are infected and they don’t fare well. The worm produces thousands of young in the body of its hapless host, and the little worms make their way into the outside world via the fly’s ovaries. Not only does this severely slash the fly’s lifespan, it also always sterilises her. But according to John Jaenike from the University of Rochester, the fly is fighting back.