Figure 1. Top: A Hubble Deep Field image with thousands of distant galaxies. Source: NASA/ESA. Bottom: A microscopic field of view from the swamp moss microbiome. Photo credit: Scott Chimileski
You may be elated by the recent presidential election in the United States. You may be devastated. No matter what, it’s a major change and at times like this, physicists share spectacular images of the cosmos as a way of comforting our worries. The Deep Fields of NASA’s Hubble Space Telescope reveal thousands of galaxies that are invisible to the naked eye but nevertheless exist in every patch of the night sky. These scientists challenge us to consider Earth and everything that happens here as infinitesimally small. We all live together on a tiny speck of rock—one of billions of planets in the universe. It is a powerful argument for unity, communicated by the astronomer Carl Sagan in the 1994 book, Pale Blue Dot.
I will offer a different approach as a microbiologist. I will compare Hubble Deep Field images to images captured through a microscope. Because the biodiversity of the microbial ecosystems that surround us each day can trigger the same invigorating perspective of nature.
Take the example of a humble patch of swamp moss. Examining the moss, we first find a thin film of water mixed with a bit of dirt on each and every minute leaf. Then, looking at this water with a light microscope, we discover thousands of bizarre microscopic animals, bacteria and other microbes scattered among bright quartz particles. This is the swamp moss microbiome. It could be right outside in the backyard, yet it is like any Deep Field of the universe—far beyond the province of human politics.
Our most advanced modern day optics cannot resolve details of stars and planets within distant galaxies in Hubble Deep Field images. We see that the galaxies were there and we see what they looked like, but not much more. There could be alien life hidden in these very images, entire worlds lost in a single pixel.
Microscopic fields of view of the swamp moss microbiome are like Hubble Deep Fields of the cosmos. Although unlike those faint galaxies, when we use light microscopy to look at moss leaves, we know that alien life is right there before our eyes. Yes; alien life... on Earth… in the most familiar places. It is alien not because it comes from elsewhere, but because so much of it is beyond our ability to isolate and culture in the laboratory. Newly discovered groups of bacterial and archaeal phyla have effectively doubled the known phylogenetic diversity within the biosphere. And we have never collected or even seen most of these species in the wild. It’s a frontier in biology.
There is more life at smaller size scales. At higher magnification, we start to see relationships among species. It’s a world of delicate structured biofilms and other communities, many of which contain photosynthetic cyanobacteria that autofluorescence red and other naturally pigmented organisms. Let’s designate higher magnification fields of view of communities and individual micrometer-scale organisms as ultra-microscopic fields. They are comparable to the Ultra-Deep Fields of the Hubble Telescope.
The last size scale to consider is one step past the Ultra level. Here we compare to another real NASA term, the Hubble eXtreme-Deep Field. xExtreme-Deep Fields record light from the edge of the universe, from galaxies that existed 450 million years after the Big Bang. Extreme fields within microbiomes push the resolution limits of light microscopes. This is the domain of the smallest biological structures and phenomena: ultra-small bacteria and archaea, transient cell-to-cell interactions, communication molecules, viruses, vesicles, and maybe species that we miss entirely, the so called biological dark matter.
If we lose our bearing while extremely zoomed on the swamp moss microbiome, we will eventually be jolted back, terrified by what appears to be a giant monster crashing through the field of view. What is this creature? It is a tardigrade. It is an eight-legged creature first studied by a German zoologist in the 1700s, who named them kleiner Wasserbär, little water bears.
Tardigrades are animals like any other, only too small for us to see. They lumber across invisible landscapes on moss, lichen, in soil, and in just about every other environment. We’ve all likely eaten a tardigrade or two without knowing it on fresh leafy greens. And they have another neat feature: they are eutelic. This means they develop into adult bodies with a finite number of cells, between 1,000 and 10s of thousands depending on the species.
The tardigrades in the swamp moss microbiome live without laws and authorities as we know them. Although, there is a kind of natural order. There are predators and prey, food webs, physical forces, and ecological cycles governing the actions of these organisms. Tardigrades react to what they might prey upon and to what might prey upon them. Whenever they are hydrated and active, not curled up in a cryptobiotic state to survive environmental stresses, they’re searching for food. Some tardigrade species feed on plant fluids; some eat bacteria; and some are predators that hunt down other microanimals, like rotifers. In turn, tardigrades are preyed upon by nematodes and occasionally, by other predatory tardigrades.
Microscopic fields of view and Hubble Deep Fields both produce breathtaking images of nature. One of these perspectives is not better than the other. They are complementary. It is an awesome feeling to find our place within the cosmos and to find our place here on Earth within the great web of life, as one species within millions, living and extinct. It is a feeling that we are lucky to be alive, lucky to be human, capable of breaking free from the violent food webs of the natural world, from biology red in tooth and claw: the everyday events of micro- and macroscopic jungles across the planet. We steer our destinies as individuals and as societies. And in doing so we have created all the wonderful aspects of culture, from art, to science, to democracy.
Look at the little water bear. She searches through the swamp moss for food. Place yourself in her view of life. She does not care, she does not have the capacity to care, about politics or any of the events that worry us. Think, how far removed we are, up here five feet tall, from all of these unseen ecosystems. How many layers of life are there—how many alien microbes here on Earth?
- What is a Tardigrade?