8 Tiny Organisms Earth Can't Live Without

By Stephanie Rogers

Our planet is home to about 5 trillion trillion bacteria, a number that seems too huge to contemplate. That may sound scary to people who think of bacteria as nasty little bugs that just want to make us sick, but the fact is, tiny organisms like bacteria, fungi and protists are absolutely essential both to the health of our bodies and to that of the entire planet. Unseen and under-appreciated, these organisms play a huge role in marine food chains, the growth of forests, climate change and our own digestive systems.

Lactobacilli in our digestive systems
We've got ten times more bacterial cells in our bodies than cells of our own. In fact, fully 10% of our dried body weight is made up of bacteria, and most of that isn't the harmful sort that causes infection, illness and tooth decay. Scientists are only just beginning to explore what they're now calling the "human biome," and they haven't yet identified most of the bacteria that our bodies host. But we do know that over 500 species of bacteria take up residence in our intestines alone, and these microorganisms may just be the most important ones in our bodies. It's hard to narrow down just which species of gut bacteria is the most important, but there's one that stands out for its sheer bad-bacteria-fighting power: Lactobacillus acidophilus. This acid-resistant bacterium colonizes the lining of the small intestine, and also covers the lining of the vagina, cervix and urethra. Producing lactic acid, L. acidophilus helps our bodies fight virulent strains of E. coli, Staphylococcus aureas, Salmonella, Candida albicans, Listeria and other types of bacteria that we really don't want getting comfortable in our bodies. This is exactly why you should be eating foods that contain live probiotics, like yogurt.

Marine bacteria that produce oxygen
Likely the most abundant photosynthetic organism on earth, Prochlorococcus is a genus of tiny marine cyanobacteria with an especially high concentration of chlorophyll. In fact, though you've probably never heard of it before, this microorganism may be the most plentiful species on earth, with 100,000 cells found within a single milliliter of sea water. Amazingly, these microscopic bacteria account for an estimated 20% of the oxygen in the Earth's atmosphere, so they provide a lot of the air we breathe. Prochlorococcus are also among the beneficial marine microbes involved in oceanic nitrogen cycles, fixing nitrogen in the water so that the entire food chain can flourish.

Mycorrhizal fungi help feed plants
Nearly every plant growing on this earth is host to parasites called Mycorrhizal fungi. Forming an extensive network of pseudo-roots attached to the plant's actual roots, these fungi can increase the plant's water and nutrient uptake between 10 and 1,000 times. Plant roots can't always take up certain minerals own their own, especially in alkaline soil, but the fungi can access the minerals and make them available to the plants.These fungi can also help protect plants that are rooted in soils with high concentrations of toxic metals, probably because the metals bind with the fungi instead of being taken up by the roots of the plants.

Bacteria that create rain and snow
Microbiologists recently made a very surprising find: living microorganisms that get blown into the sky, including bacteria, fungi, diatoms and algae, can be used by clouds as precipitation starters. One researcher at Montana State University discovered that bacteria was highly concentrated in the innermost core of hail stones, learning that the bacteria allowed the ice to form at warmer temperatures than normal. This discovery will likely spur more research into just how big of a role microbes play in weather cycles.

Protists at the bottom of the food chain
Mostly unicellular, protists have evolutionary histories that stretch back at least two billion years. While some protists aren't seen as beneficial - like the genus Plasmodium, which causes malaria - these microscopic organisms are a critical part of marine food chains. For example, diatoms, a type of protist, serve as the main base of the food chain in both fresh water and ocean habitats, supplying calories to larger protists which are then eaten by small animals, and so on.

Moss bacteria that help forests grow
Ancient trees aren't just beautiful examples of the natural world. They're also hosts to species of moss that contain crucial bacterial which are twice as effective at "fixing" nitrogen as the species that live in the soil. Highlighting the importance of maintaining old-growth trees, especially those in coastal temperate rainforests, a study on these cyanobacteria found that they take nitrogen from the atmosphere and make it available to plants in a highly efficient way that few other organisms can match. That means that old growth trees covered in moss can actually help the forests around them grow.

Bacteria and fungi that break down organic matter
Decomposition is a complex process involving hundreds if not thousands of different organisms, like earthworms, millipedes and maggots. But behind the scenes, it's really the bacteria and fungi that do most of the work turning dead organic matter, from wood to human bodies, into nourishing soil. Consuming the dead organic matter for energy, bacteria help to recycle nutrients like nitrogen and carbon back into the life cycle.

Microbes that help regulate climate
Aside from seeding clouds with precipitation, microbes play another role in weather and climate: storing and producing even more carbon dioxide than all of the earth's trees and plants. Microbes help the world's soils store more than 2.5 trillion tons of carbon, while photosynthetic bacteria in the oceans pump 55 billions of carbon dioxide into the atmosphere every year - eight times the amount we humans produce through fossil fuel burning and deforestation. But as the Arctic tundra starts to melt as a result of climate change, microbes have been able to flourish in a previously inhospitable region, breaking down organic matter and releasing even more carbon dioxide. Scientists are still studying just how this will affect the pace of climate change.

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Photo: Colin-47