Microbes: Undersized, overlooked organisms that hold the key to understanding life on Earth
Money doesn’t make the world go around. Microbes do.
Be it ever so humbling to our human-centric view, “microbes shaped the biosphere in a way that gave humans a chance to evolve and make a living,” said WHOI microbiologist Andreas Teske.
Billions of years ago, ocean-dwelling bacteria capitalized on a chemical reaction now called photosynthesis and filled Earth’s atmosphere with oxygen, setting the stage for the evolution of terrestrial, multicellular life. Today, unseen, ubiquitous microorganisms still attend to the crucial biochemical reactions that keep the planetary ecosystem in balance. These armies of single-celled catalysts are at the front line, continually making, moving, breaking down, and recycling the essential chemicals of life.
“Just by existing, microbes produce and release chemicals as metabolic byproducts, which change their environment—our environment,” said Katrina Edwards, a WHOI geomicrobiologist, who studies the fundamental but often overlooked roles microorganisms play in shaping the earth.
Some use water to produce the oxygen we breathe and carbon dioxide to produce the food on which the ocean’s animal life depends. Some convert sulfur beneath the seafloor into organic materials, launching the food chain on which deep-sea life depends. Others decompose organic materials on land and sea to be reused in an ongoing cycle. Some microbes even dissolve rock into liquid that returns via rivers to the ocean.
“These are the most important organisms on our planet,” said Michael Atkins, who earned his Ph.D. in biological oceanography at WHOI in June.
The world’s microorganisms come in an amazing variety of forms spread among three distinct domains of life: bacteria, nuclei-containing eukaryotes (which include all fungi, plants, and animals—a large number of which are single-celled), and archaea, recognized as a distinct domain only over the course of the last two decades. Though archaea, like bacteria, are single-celled prokaryotes (microbes without cell nuclei and other organelles), they are “as different from bacteria as bacteria are from trees,” said WHOI marine biologist Carl Wirsen.
Many of these microorganisms can thrive in every conceivable (and a few almost inconceivable) environments—in boiling hot springs, in the sunless, high-pressure depths of the ocean, in Antarctic ice, in desert soil, in acidic waters that would dissolve your skin, or in the stomachs of cows or deep-sea tubeworms.
“No matter how extreme an ecological niche or a particular chemical environment is, you can find some microbes that are adapted to it and taking advantage of it,” said Teske, who last year helped identify the world’s biggest bacterium, which prospers in sulfide- and nitrate-rich, but oxygen-poor sediments off the Namibian coast. “Almost any energy-yielding chemical reaction that exists has been exploited by microorganisms.”
For all these reasons, microorganisms hold the key to understanding the evolution of Earth and life on it.
En masse, they effected the chemical transformations that spawned the planet’s air, soil, and oceans. Today, they are still the worker bees of the planetary hive, on whom the health of the entire ecosystem depends. Will global warming spark wholesale changes in the ocean’s microbial population, or will microorganisms help us by absorbing the excess carbon dioxide humans are putting into the atmosphere? Is excess fertilizer runoff into the ocean disrupting natural food webs? There are telltale signs: Harmful algal blooms—the proliferations of single-celled toxic marine plants that overwhelm coastal areas—have been occurring with increasing frequency and severity around the world, causing health problems and millions of dollars of damage to fisheries, aquaculture, and tourism industries. In other areas, rampant algal growth also has sucked the oxygen out of ocean waters, creating and expanding “dead zones” where other marine life cannot live. On land, Edwards discovered a new species of archaea that dissolves rock into powerful acid. When long-buried rocks are exposed by human mining activities, their acidic runoff can cause devastating and expensive contamination in groundwater, rivers, and the sea.
Until we can comprehend all the diverse life forms out there and how they interact, we can only grope blindly as we try to figure out how to protect ecosystems from the excesses of human activities. On the other hand, oil-eating or toxic waste-degrading bacteria, recently discovered archaea that consume the greenhouse gas methane, or other microbes we have yet to discover could help us remediate environmental problems.
On a microscopic level, microorganisms are the laboratories of life. For billions of years, they have been experimenting with chemical reactions that occasionally prove marvelously efficient and launch life into entirely new directions.
“They invented all the biological structures and metabolic processes of life—many of which were retained by multicellular forms,” Teske said.
Scientists believe, for example, that chloroplasts (the organelles within plant cells that are responsible for photosynthesis) and mitochondria (the organelles in animal cells that convert sugars into energy) were both free-standing microorganisms that were literally incorporated into eukaryotic host cells somewhere along the evolutionary line. Undoubtedly, the architectures and processes that occur within our own human cells were pioneered by microorganisms, so we can also learn a lot about ourselves by studying them.
WHOI scientists increasingly are using emerging techniques spawned by the biotechnology revolution to look for genetic differences in microbes, which are often impossible to distinguish by examining their physiology, and to identify genes that have been retained as life evolved. Atkins this year found a single-celled microorganism living near deep-sea hydrothermal vents that may be the closest to the common ancestor from which all multicellular fungi and animals emerged.
Newly discovered microorganisms also offer the potential to find compounds or enzymes with pharmaceutical or industrial uses. Only a few years ago, in a previously unknown microbe thriving in a hot spring in Yellowstone National Park, scientists found a heat-resistant enzyme. It became instrumental in the polymerase chain reaction (PCR), a widely used technique to replicate DNA rapidly that sparked the modern revolution in biotechnology. Mining industries are economically extracting metals from ores using huge vats of microorganisms with abilities similar to Edwards’s archaea.
“People would be surprised to see how far bacteria have penetrated into everyday life,” Teske said. “Bacterial slimes are widely used in the food-processing industry, for example, because these polysaccharides create the perfect consistency for ice cream. Certainly there are living things out there doing potentially useful things that haven’t been found or invented yet.”
“Out there” also includes places beyond Earth—on other planetary bodies. The search for extraterrestrial life today does not focus “on little green men,” Teske said, “but on microbes.” For they are the ones that have found ways to adapt, survive, and even thrive in a wide range of seemingly harsh conditions.
Out there is “a living minestrone, with the majority of bits small or microscopic,” Sylvia Earle, the world-famous oceanographer and a WHOI Trustee, wrote in The Living Ocean. She was referring to the ocean, but microscopic life also thrives in the rocks on land, beneath the seafloor, and perhaps elsewhere in the universe. We’re just beginning to open our eyes to their realm.
This issue of Currents introduces some interesting microbes, from each domain of life, that were unknown until last year—and the WHOI scientists who discovered them.