Planet Earth

Chasing the Limits of Life with 'The Extremo Files'

By Jeffrey MarlowSep 3, 2015 12:20 PM

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Seafloor chimneys at hydrothermal vents host a zoo of unique life forms. (Image: NSF / NOAA / WHOI)

When most people think about biology, they think big: dolphins or elephants, rain forests or wide open prairies. These animals and their habitats are, after all, the best studied and most visible signs of life; but really, it’s a microbial world and we’re just living in it. Microorganisms underlie many of the most fascinating and potentially transformative questions in modern science, from the next round of medical breakthroughs to the architecture of global elemental cycles and the search for life beyond Earth.

Multi-celled creatures may have cornered the market on morphological complexity, with their scales, hooves, wings, talons, and tendrils, but microbes are the biochemical savants. In the service of building proton gradients and harnessing them for an energetic windfall, Bacteria and Archaea have developed an arsenal of metabolic inventiveness. They can handle sub-zero temperatures, breathe solid iron, and survive an interplanetary journey. They’ve colonized nearly every possible corner of the planet, including deep coalbeds beneath the seafloor, animal gut tracts, uranium mines, and parched desert soils. These organisms are often colloquially termed “extremophiles,” given their affinity for anthropogenically-determined “extreme” conditions. And we’re just beginning the long, exciting journey to probe the limits of metabolic possibility, with jaw-dropping biochemical feats making the scientific headlines nearly every week. We simply don’t know what these single-celled life forms may be capable of.

The Power of Microbes

Microbes are individually diminutive but collectively prodigious. Their remarkable pervasiveness – a single pinch of your average soil can have billions of cells – means that a single organism’s biochemical transformations are multiplied by many orders of magnitude. What results is a microbially dominated planet. Greenhouse gases like methane are strongly controlled by microbial communities, and only microbes can access N[[Export Error -- Unsupported HTML: <sub>2</sub>.]] – the otherwise inert gas that forms nearly 80% of our atmosphere – and turn it into nitrogen-based molecules that are absolute requirements for all life.

Understanding how the roiling communities of individual cells interact with each other and shape their surroundings – a local geochemical system or an animal host, for example – are foundational questions of microbial ecology. As analytical tools improve and additional habitats are explored, mind-bending hints at the weird, alluring power of microbial systems are emerging. Some parasites can turn host genes on and off, exerting a sort of “mind control”; the community of microbes in your gut can influence everything from your weight to your behavior; metal-breathing cells that can be harnessed to generate a small electrical current in “microbial fuel cells.

Custom Creations

While some microbiologists are hoping to understand natural microbial capabilities, others are starting to tinker with their inner workings. This is the new field of synthetic biology, a shotgun marriage of engineering and microbiology in which cells are designed or directed to bespoke needs. Synthetic DNA, more affordable than ever, can be pieced together to develop new genetic circuits. In order to build a better enzyme, researchers can nudge microbes down a directed evolutionary path, prompting an accelerated move toward optimality. Gene editing techniques like CRISPR-Cas, the relatively simple way to remove, alter, or amplify nearly any gene of choice, are game-changers, leaving bioethicists and regulators playing catch-up. These powerful tools are diffusing through labs around the world, and while the primary efficacy is largely promising, side effects and system-wide repercussions need to be examined in the coming years.

An artist's rendering of the ocean beneath Europa's icy crust. (Image: NASA/ Britney Schmidt/Dead Pixel VFX/Univ. of Texas at Austin)

Life Beyond Earth?

Finally, the reductive examination of extremophiles on Earth is driving the search for life elsewhere in the universe. Understanding exactly how biology works – in parallel with the geological and geochemical exploration of new worlds – can show us what to look for as astrobiological missions go forth into the Solar System and telescopes gaze into the atmospheres of exoplanets. The discovery of life beyond Earth would be one of the most important de-centering discoveries in human history, analogous to the findings of Copernicus or Darwin, and microbes may well be the key.

The wide range of microbial frontiers is formidable. Connected by a common biochemical lexicon and a set of traits that confer vitality, microbes are remarkably diverse. The Extremo Files will navigate these byzantine networks, tracking cutting edge microbiological research as we build a better understanding of what exactly biology is, what it can do, how it shapes our world, and what these smallest organisms may have to tell us about our place in the universe. I'll also be profiling some of the exciting expeditions and exploratory adventures that are broadening our knowledge of the natural world.

Biology is poised at a fascinating place: the coinciding exploration of new natural systems and engineering of known organisms will no doubt make for some exciting findings in the coming years, exposing the limits and potential of life.

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