When most people hear the words “bacteria”, “virus”, or “microbe”, their mind turns to thoughts and images of mold growing on oranges, outbreaks of influenza, and infected humans turning into zombies. However, there is so much more to microbes than just the story line of the next blockbuster movie. They were the foundation for all life that followed them and they are also the reason we are still here.
Microbes are essential for our continued survival on Earth. They were the first lifeforms on the planet, appearing roughly 3.8 billion years ago and they are responsible for the oxygen that has allowed aerobic life to expand into all corners of the globe.
Beginning about 2 billion years ago, microbes such as cyanobacteria and Prochlorococcus, developed the ability to use photosynthesis for energy production and began to release oxygen as a byproduct. Since aerobic metabolism is much more efficient at producing ATP needed for cellular energy than anaerobic metabolism it allowed for an explosion of aerobic multi-cellular organisms to arise. The increase in atmospheric oxygen allowed larger and more complex life forms to evolve which led to creation of eukaryotic organisms such as humans.
Image 1. Cyanobacteria – one of the microbes responsible for the Great Oxidation event of the atmosphere about 2 billion years ago.
Imaged retrieved from https://pmc.ncbi.nlm.nih.gov/articles/PMC8960603/.
While trees and other plants are important contributors to sustaining atmospheric oxygen, they only contribute a small portion. Oceanic organisms, such as cyanobacteria, algae, and other microbes, such as Prochlorococcus, are the major sources of oxygen production. Recent research has suggested that Prochlorococcus may actual produce more oxygen than cyanobacteria and may be responsible for most of today’s atmospheric oxygen.
Image 2. Prochlorococcus – a marine organism responsible for producing a large portion of atmospheric oxygen.
Image retrieved from https://pmc.ncbi.nlm.nih.gov/articles/PMC8960603/
Microbes play other important roles in sustaining life on our planet too. They are an integral part of biogeochemical cycles and act as catalysts for the transformation and exchange of nutrients and elements. Some microbes help to break down organic matter, such as dead plants and animals, back into simple elemental nutrients, such as carbon, that can then be used by living plants, animals, and other microbes to sustain life. Microbes can also help to sequester carbon in the soil preventing it from being released as carbon dioxide into the atmosphere and allowing it to be used by plants in the future. Other microbes have formed symbiotic and/or mutualistic relationships with plants providing them with needed nutrients in exchange for other resources. For example, Rhizobium, a nitrogen-fixing bacteria, changes atmospheric nitrogen into ammonia which can be used immediately by the plant while mycorrhizal fungi help improve the uptake of phosphorus from the soil by a plant’s roots.
Image 3. Microbial contribution to the soil carbon cycle.
Image retrieved from https://www.annualreviews.org/content/journals/10.1146/annurev-environ-012320-082720.
Plants aren’t the only species that require microbes to survive. Microbes are also essential for human survival. Humans evolved around microbes and they became an integral part of our day to day existence. Microbes can be found in our intestinal tract, in our mouths, on our skin, and everywhere in between. Their relationship with us can be mutualistic, commensalistic, or pathogenic depending on the type of microorganism and where on our bodies it finds itself. Microbes found in the gut help to shape our adaptive and innate immune systems. Research has shown that people who have had exposure to a wide array of microorganisms tend to have less allergies than those whose exposure was limited. Gut microbes also play an important role in helping to digest food and in synthesizing important nutrients such as vitamins and short-chain fatty acids. Microbes on the skin and in the respiratory tract help to maintain homeostasis by competing against pathogenic microorganisms. Some microbes also help to balance the pH of the skin and assist with wound healing by stimulating cellular repair processes.
Image 4. Microbes found in different areas of the human body.
Image retrieved from https://www.nature.com/articles/s41392-022-00974-4.
Microbes are necessary for producing many of the different foods and drinks that we use on a daily basis. For example, Enterococci are used to help ripen cheese while different species of Saccharomyces are used to make bread and in the fermentation processes of beer and wine. Other microbes can be used to create substitutes to traditional meat and dairy food sources which can help reduce the impact that food production has on the environment. They can also be used to help preserve food through the use of vinegar which is made using microbes.
Image 5. The role microbes play in food production.
Image retrieved from https://www.nature.com/articles/s41467-023-37891-1.
Microbes have also been used in medicine to prevent and treat disease. Some pathogenic microbes, such as Mycobacterium and Listeria, are useful as vaccine vectors as they cause the immune system to react quicker than other types of vectors. Antibiotics made from one microorganism may be used to help treat an infection caused by another microorganism. Penicillin, which is derived from a fungus, is used to treat certain bacterial infections. Since the 1940s species of Streptomyces have been used as chemotherapeutic agents to treat different types of cancer and leukemia. Perhaps the most exciting and promising use of microbes is the development of the Class 2 Type II CRISPR‐Cas9 system from Streptococcus pyogenes which can be used to edit the genetic code. As research into this technology continues it may eventually be used as a treatment option to help those with severe diseases caused by genetic mutations.
Image 6. Fungal mold growing on media. Penicillin, one of the first antibiotics, is from a fungus.
Image credit: Shutterstock.
Microbes are key components to our continued survival here on Earth. They are essential for oxygen production, biogeochemical cycles, food production and preservation, and human health. We have only scratched the surface of the importance that microbes have in our lives. Future advances in science and technology will continue to unlock the secrets of microbes and use them to improve our planet and our lives.