【英语学习】【Study English】03.05.2021
Earth's original inhabitants -- and their role in combating climate change.
Steven Allison
Microbes are everywhere. They live in the air, the ocean, the soil and on our bodies, lots of them. But before you reach for the hand sanitizer, take a look at these beautiful bacterial mats in Yellowstone's Grand Prismatic Spring. They’re absolutely amazing because they’ve somehow figured out how to grow happily at near boiling temperatures. Ever since life on Earth began, probably in a place like this, microbes have kept planetary chemical cycles in balance. Today, humans are altering that balance and changing the climate by emitting greenhouse gases into the atmosphere. But microbes might be able to help us with our climate problem. After all, microbes are Earth's original and most adaptable inhabitants.
Now, I know that not everyone is so enamored with microbes. My biology students tell me that they usually think of "pathogen" when they hear the word "microbe" and I know we're in the middle of a global viral pandemic. But you should keep in mind that far less than one percent of microbial diversity is actually pathogenic to humans. In fact, most of the microbes we encounter are beneficial. There are trillions of bacteria, fungi and viruses living in and on us right now, more of them than human cells in the body. They help us digest our food, protect us from disease and maybe even choose our mates. Microbiologists call this assemblage of tiny interlopers the human microbiome.
We now know that there are microbiomes in basically every environment. In the same way that they help our human bodies stay healthy, microbiomes in water, soil and air are critical for planetary health. For example, cyanobacteria in the ocean carry out photosynthesis and provide a large fraction of the planet's breathable oxygen. Even though they're tiny, their green color can be seen from outer space with satellites. They may be harder to see, but microbiomes in the soil are just as important as the human or ocean microbiome.
I think about soil as a skin for the planet that provides nutrients to sustain crops and other plants. As an ecologist and climate scientist, I've been studying the microbes that live in soil for 20 years now. Just like we've seen with the human microbiome, cutting-edge techniques in molecular biology, especially DNA sequencing, show that soil microbiomes are extremely diverse in their genes and life cycles. Scientists are starting to figure out how we can harness the diversity of these often invisible organisms to solve global problems like climate change and food insecurity.
Take agricultural crops, for example. With climate change causing more frequent heat waves and droughts, crop plants may become stressed, reducing yields and threatening food security. But microbes can help. There are symbiotic fungi called mycorrhiza that grow out from plant roots and into the soil where they collect water and nutrients. Then the plant and its symbiotic fungus make a trade. The fungus sends water and nutrients into the plant roots and the plant pays back the fungus with sugars from photosynthesis. To reduce stress on plants from climate change, farmers can inoculate the soil with these beneficial fungi. Land managers are also starting to use the same approach to help native plants recolonize degraded soil during habitat restoration. So the next time you support an environmental cause, maybe through a nonprofit donation or volunteer work, remember, soil microbes need conservation too.
The planet also relies on soil microbiomes for other essential services. Have you ever thought about what happens to living things like these leaves, mosses and mushrooms when they die? I'm not talking about an existential crisis. I'm talking about microbial decomposition. Think about it like a type of biological recycling practiced by very diligent microbes. They take dead bodies and turn them into useful nutrients. Without this essential service, life on Earth would grind to a halt because dead stuff would pile up, depriving the next generation of life forms of the raw materials needed for growth.
Hundreds of researchers funded by the US Department of Energy are even trying to figure out how to co-opt microbial decomposition to produce sustainable biofuels from wood, grasses and other plant materials. Fuels derived from plants and microbes are part of the climate solution because they don't rely on fossil carbon sources like coal and oil. At the same time, ecologists like me are very concerned about how climate change might affect microbial recycling in the environment. A warming climate might speed up the process and release more greenhouse gases into the atmosphere. A drier climate might slow down the microbes and leave plants starved for essential nutrients.
Fortunately, there is reason for hope. Microbes are super adaptable because they can evolve very quickly. For example, you may have heard of pathogenic bacteria like staph evolving antibiotic resistance. Of course, that's bad for us. But the same evolutionary process could also help microbes adapt to climate change, which is good. After all, microbes evolved long ago to survive extreme conditions like the hot springs of Yellowstone. Just like our human cells, each microbial cell contains a genome. And just like our genomes, microbial genomes contain genes or DNA sequences with instructions for growth and survival.
My colleagues and I have identified genes that allow bacteria and fungi to survive drought and decompose dead plant material. We're currently doing experiments to see how fast these genes evolve and what kinds of genetic changes make bacteria and fungi more resistant to drought. Some of our prior research shows that microbes have the potential to deal with climate change. Microbiomes and the services they provide could cope not just by evolving, but also by shifting around the dominant species of microbes.
Microbiomes are so diverse that even if some of the species die out with climate change, others might survive and take their place, allowing nature's recycling to continue.
To test this idea, my colleagues and I designed special cages to contain microbiomes from different habitats in Southern California. We sampled microbiomes from places ranging from forested mountaintops to hot deserts. Each cage contained a microbiome from one of these places along with sterilized dead grass for the microbes to use as a food source. We then put the cages back into the different habitats so that the microbiomes experienced pretty dramatic changes in climate. We expected that the microbes from the cooler places would die out when we moved them to the warm places like the hot desert, and that they would lose their ability to consume and recycle the nutrients in the dead grass material.
But when we looked at the results, I was really shocked. The microbiomes were almost unfazed by this massive climate difference. There were some changes in the dominant species, but mountaintop microbes decomposed dead grass just as well as desert microbiomes in the hot, dry climate. This result tells us the microbiomes have the ability to evolve and shift to deal with really dramatic climate changes.
Another way that soil microbiomes can be part of the climate change solution is by building healthy soil. Many soil bacteria and fungi ooze out sticky chemicals to glue themselves onto soil surfaces. The glue and the microbes form these biofilms that hold soil particles together. This helps the soil resist erosion and hold more water that's available for plants.
Microbes and their biofilms also play a big role in soil carbon sequestration. Many forms of carbon from plants, like sugars, don't last long in the soil because they're food for many organisms, including the microbes. But microbodies and biofilms are made up of complex chemicals. For example, many microbes build cell walls for protection, so the wall material has to be resistant to biochemical attack. When the microbes die, their corpses, especially those cell walls, can stick around for a really long time, maybe even thousands of years. In this way, soil acts a lot like a bank vault for carbon. More carbon in the bank means healthier soil and less greenhouse gas buildup in the atmosphere. Microbes are sort of like the Federal Reserve. They can take cash off the street in the form of these plant sugars and lock it away in a chemical vault for long-term storage.
With the science of climate change becoming more and more obvious every day, we need to figure out how to adapt, for sure. Some scary outcomes, like emerging microbial diseases, are definitely something we need to plan for. But microbes can be a part of the climate solution if we figure out how to leverage all that microbiome diversity.
To be honest, though, making sense out of complex microbiomes is still a big scientific challenge. Their complexity is both a blessing and a curse. We're only beginning to understand all the strange and wonderful microbial lifestyles that have been evolving since the origins of life on Earth. This digital artwork called "Microbes Reimagined" does a great job of capturing that sense of mystery. But one thing we do know for sure is that microbes are not just pathogens. Our lives literally depend on them. So next time you take a breath outside, imagine all those oxygen-spewing cyanobacteria floating around in the ocean, and when the time comes and you draw in that last and final breath, take comfort in knowing that soil microbes will be there to turn your body into useful nutrients.
Even as we enjoy these benefits of microbiomes, climate change remains a potentially existential threat to our well-being. But dangerous climate change is not inevitable, at least not yet. With the right cutting-edge research, diverse microbiomes could become a big part of the solution to our climate problem.
Source: TED
