Life keeps turning up in the strangest of places. Hardy microbes have been found not only to survive, but to thrive, in the driest deserts of the world, under kilometres of ice near the poles, and around scalding hot, poisonous vents in the deep ocean.

Now Australian scientists have discovered the deepest, and possibly the oldest evidence, of living bacteria ever identified.

Home for these bugs is a subterranean hell hole: a dark, hot, oxygen-free region two kilometres underground where the bacteria feed off oil reserves in sediments up to 145 million years old.

"It’s a hostile and extreme environment," says Professor Kliti Grice, of Curtin University of Technology in Perth, whose study with Australian and German colleagues in three oil producing regions in the Middle East, central Europe and South America was published recently in the journal Nature Geoscience .

Microbes – organisms too small for the eye to see – often get a bad rap. And it is true that they can cause lots of disease, rot our teeth, spoil our food, and might even be making us fat, if recent research showing particular kinds of gut bacteria regulate body weight is confirmed.

But they are also amazing creatures, and we should be grateful to them, says Idan Ben-Barak, a Sydney scientist who sings the praises of bacteria, viruses, fungi and other tiny lifeforms in a book, Small Wonders, How Microbes Rule Our World .

"It’s a simple point, but one that occasionally needs to be hammered in: life on Earth relies completely and utterly on the existence and actions of microbes," says Ben-Barak, who trained as a microbiologist in Israel, and is now working towards a PhD in the history and philosophy of science at the University of Sydney.

More than 2 billion years ago they were the "original solar panels", capturing sunlight and producing the oxygen that kickstarted the evolution of more sophisticated lifeforms. And today they help regulate climate as well as being the beginning and end of the food chain, helping larger creatures survive, and then turning them back into dust when they die.

The book, his first, is a tribute to how varied life on Earth is, including the strange social tricks, warfare strategies, and methods of travel that microbes have developed in their battle to cling to life.

The fastest moving creature in the world, for example, is a microbe that looks like a tiny comma, called Bdellovibrio bacteriovorus . Using rotating tails, known as flagella, it can zoom along at 160 micrometres a second – the equivalent of a human swimming the length of three olympic pools in a second. It likes to feast on a variety of other bacteria, and detects its prey chemically before going in for the kill.

With antibiotics losing their effectiveness this means the fast-moving microbe could have a future as a medicine, killing deadly bacteria, speculates Ben-Barak. "Wouldn’t it be great to know that our medicine takes the form of a rushing, ravenous, ravaging, microscopic killer comma?"

Other microbes have also developed exceedingly clever ways to get around, particularly the dung-loving fungus, Pilobolus crystallinus .

While its spores are maturing, it grows a stalk with a sac at the top and then pumps water into it. When the water pressure is released, the spores can fly to a height of two metres, landing up to 2.5 metres away. "That’s not bad for a centimetre-long cannon," he says in his book.

What’s more, the fungus aims towards the sun, increasing the chances of the spores landing on a sunny bit of grass where a grazing cow might gobble them up, eventually excreting the spores in a fresh new home of dung.

Communication between microbes is surprisingly sophisticated, and they can have altruistic streaks, sacrificing themselves for the greater good. A predatory bacterium, Myxococcus xanthus , is a good example of this, says Ben-Barak. It hunts other microbes in swarms, like a "sci-fi-esque, alien-looking blob".

But when times get tough, and food is short, more than 100,000 of the tiny bugs join forces and build a structure which houses hardy spores. Although this ensures their species’ survival, about three-quarters of the original bacteria die in the process.

Long before humans even knew microbes existed, they put them to good use, to help make wine, beer, bread and yoghurt. Today many medicinal products, such as vaccines and antibiotics are produced using microbes. And one of the most important roles for the tiny creatures in future will be to clean up toxic waste, says Ben-Barak. "Incredibly, for nearly every chemical that human ingenuity has devised, there exist organisms able to deal with it."

The Australian scientist Megh Mallavarapu has discovered some of these super-bugs, including soil bacteria that can destroy some of the worst cancer-causing agents, such as benzene and toluene, as well as an arsenic-eating one that happily dines on deadly pollutants from mines and farming.

His team screened thousands of samples of microbes from arsenic contaminated soil to find the bugs which are harmless to people and the environment, but which can efficiently convert the most toxic form of the heavy metal to a less dangerous substance.

"It was a case of serendipity. There are so many microbes in the soil we might easily have missed it," says Professor Mallavarapu, from the Co-operative Research Centre for Contamination Assessment and Remediation at the University of South Australia.

Hopefully the microbe will one day be put to use cleaning up drinking water for tens of millions of people in Asia as well as sites in Australia and elsewhere that have been polluted by arsenic-based products used in stock dips, timber posts and gold mining, he says.

On the other hand, the problem with the bacteria that Grice and her colleagues found deep underground is that they are degrading the oil. The research, which has identified substances from cell membranes of the bacteria, could provide clues for industry as to why petroleum reserves around the world vary so much in quality.

But the discovery of the tough little bugs could also have wider implications, including the search for life on other planets, says Grice. "These organisms we’re finding in extreme environments may be like the ones you will find on Mars."

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