A spoonful of soil, a drop of seawater and the human intestine look unrelated. At the microscopic level, however, all three contain busy communities that help larger ecosystems work.
“Microbe” is a convenient umbrella term, not a single branch of life. It includes bacteria and archaea, many fungi and protists, microscopic algae and viruses—the last of which depend on host cells to reproduce. Their roles are just as varied.
The planet’s recyclers
When an organism dies, bacteria and fungi help break complex material into simpler compounds. That decomposition returns nutrients to soil and water instead of leaving them locked in dead tissue. Other microbes transform nitrogen, sulfur and carbon through chemical reactions that plants and animals cannot perform on their own.
Some bacteria and archaea convert atmospheric nitrogen into forms that can enter food webs. In the ocean, cyanobacteria and microscopic algae use photosynthesis. They support marine food webs and contribute a substantial share of global oxygen production, although the oxygen we breathe reflects a long-term balance of production and consumption.
Partners, competitors and pathogens
Plants interact with microbes around their roots. Some relationships improve nutrient access; others cause disease. Animals also carry microbial communities. In humans, gut microbes help process components of food, produce certain compounds and interact with the immune system.
That does not mean every microbiome claim is proven. A microbial pattern associated with a disease may be a cause, a consequence or both. Researchers use controlled studies to separate correlation from mechanism.
Pathogens are a small but important part of the picture. Vaccination, sanitation, antibiotics and food-safety practices protect people from harmful microbes. Antibiotics work against bacteria, not viruses, and unnecessary use can select for resistant strains.
Modern DNA sequencing has revealed organisms that are difficult to grow in a laboratory. The discovery has made one point unavoidable: visible life depends on an enormous, mostly unseen network of chemical work.
Microbes are not universally helpful or harmful. They are organisms and biological agents occupying particular niches. Together, they keep nutrients moving, shape the atmosphere and oceans, and live in close partnership—and sometimes conflict—with plants and animals.
Sources
- NIH/NIEHS, Microbiome: https://www.niehs.nih.gov/health/topics/science/microbiome
- NOAA Ocean Service, What Is a Microbe?: https://oceanservice.noaa.gov/facts/microbes.html