There are so many ways we can die. There’s the rule of three: three minutes without air, three days without water, three weeks without food. We’ll die of hyperthermia after 10 minutes in 60-degree-Celsius heat, and of hypothermia when our body temperature drops to 21 degrees. At an altitude of 4500 metres we’ll pass out, and if somehow we get to 8000 metres, we’ll die. Too much UV radiation damages our DNA, too little and we can’t produce vitamin D. Result? That’s right. We die.
Fortunately, when we want to holiday, there are plenty of places where food and drink are abundant, the sun shines just enough, the air is rich and clean, and it’s 25 degrees all day long. We think we’ve got this survival thing nailed.
But it turns out bacteria do it much better.
Our planet has plenty of spots that don’t tick our boxes. Don’t even think about taking a dip in one of those colourful pools at Yellowstone National Park, or spelunking in a hydrothermal vent. The ocean floor is a truly terrible place, with crushing pressures and zero sunlight. And Antarctica is not a penguin paradise. It’s one of Earth’s most hostile environments. A few hundred metres from the water’s edge it’s a barren desert. The sun disappears for months at a time and it’s so cold that your eyeballs freeze in their sockets. Then the sun shines all the time, blasting blistering levels of UV radiation through the ozone hole.
Yet to an amazing number of microbes, all these inhospitable environments are home sweet home. Nothing, it seems, is too nasty for these tiny freeloaders. Here’s a sampling of some of their more outrageous accomplishments, curated by Monash’s expert in microbial extremism, Dr Chris Greening.
In a paper published in the journal Nature [on December 7], my team, along with colleagues at the University of New South Wales, discovered that the supposedly sterile dirt on the Antarctic continent was teeming with microbial life. How do they manage without any food and water? We analysed the microbial DNA and found species of bacteria that can scavenge nutrition out of thin air. More precisely, they were able to harvest hydrogen, carbon monoxide and carbon dioxide from the air and turn it into biomass.
The bottom of the ocean is no place for a holiday. It’s freezing cold and dark, and the water column above exerts a pressure of up to 6000 pounds per square inch. But that doesn’t stop bacteria. Along the mid-ocean ridge, shifting tectonic plates allow seawater to filter into the Earth’s crust. As the water heats up to 400 degrees, it dissolves minerals in the crust, and then this chemical cocktail is spewed back up into the ocean in the form of a hydrothermal vent. A surprisingly rich ecosystem thrives in these super-hot, high-pressure, mineral-rich environments, including thousands, even tens of thousands of species of bacteria that use these superheated mineral plumes rich with sulphur and hydrogen as fuel. The biomass produced can then go on to feed entire underwater ecosystems.
The Spirochaete family of bacteria includes some really shady members, including species that cause syphilis and Lyme disease. We’re currently studying some other members who have a predilection for toxic sites such as oil-contaminated groundwater aquifers and trichloroethylene spills. We’re finding that they work hand-in-hand with another unrelated bacterial species, taking the hydrogen produced by these buddies and using it to transform naphthalene, a toxic aromatic (think mothballs) hydrocarbon that’s a byproduct of coal mining, into biomass.
A beach is an excellent choice for a human holiday, but only on the surface. Microbes like to hang out there, too, but lacking legs, they’re constantly being buried in the sand when the tide comes in. And, as you know if you’ve been buried on a beach, there’s very little air under the surface. These environments are dominated by microscopic algae, which normally fuel themselves differently than bacteria. My team spends a lot of time doing research on Elwood beach, and we’ve helped show that these fellows can also get along just fine without any oxygen or sunlight, using – you guessed it – hydrogen to survive, in a process called “dark fermentation”. This is important because these microbes are largely responsible for turning atmospheric carbon into dissolved carbon in the ocean.
You’re probably surprised that humans are considered a toxic environment. But think about it. Very little oxygen, stomach acid, digestive enzymes, killer T-cells and bacteriophages just waiting to tear you limb from limb. But we’re home to a whopping two kilos of microbes – and those are just the good guys. Our research has shown that more than 70 per cent of the microbes in the human gut use hydrogen to fuel themselves in this anaerobic environment. Just like the algae buried on the beach, many of these bacteria use fermentation to survive.
Some bacteria in the thermal pools in New Zealand’s Taupo Volcanic Zone like it hot. Some like it acidic. Some like it alkaline. But they all like it stinky, because they fuel themselves using gases such as methane and hydrogen sulphide. Methane is an extremely potent greenhouse gas, so these methane-gobbling microbes are doing us a huge favour by preventing a lot of it from getting into the atmosphere. When we analysed samples from the pools, and from acidic volcanic soils, we found that many of them also used hydrogen as a fuel source, and that this metabolic flexibility helped them thrive. Animals that eat lots of different things are omnivores; microbes that do that are called mixotrophs. And just like in Antarctica, some of these microbes can also sustain themselves by scavenging gases from the air.
Microbes, with their ability to inhabit every nook and cranny on the planet, are an inspiration. The more we find out about their survival superpowers, the more we question our assumptions about what constitutes life. And that’s only a rabbit hole or two away from our assumptions about what conditions would be necessary for extraterrestrial life.
Back on our own planet, we can use this understanding of microbial survival in extreme environments to solve serious problems. We can harness them to help clean up toxic waste, degrade plastic, scavenge carbon dioxide and methane out of the atmosphere, and rebalance our gut flora to reduce inflammation. Maybe someday we can get them to balance budgets and design congestion-free transportation networks.
We’re lucky they’re survivors, because they may just make it possible for us to survive as well.