We don’t talk much about microorganisms in everyday life, but they’re so important. They are everywhere, in such abundance that it’s hard to grasp—just like trying to comprehend all the stars and planets in the night sky. Yet they are crucial for life on Earth, i.e., humans, other animals, plants and fungi. Since we aim to describe the interconnections within the ecosystem, with microorganisms at the core, we will provide brief information about this here. Think of us as a gutter connecting downspouts—we guide you in the right direction, but it’s up to you to decide if you want to dive deeper. You can explore more through resources like research papers, books, and other knowledge platforms.
Microorganisms, as the name suggests, are tiny organisms that are invisible to the naked eye and, therefore, often require a microscope to see them. They can be unicellular and multicellular and include bacteria, archaea, some fungi, algae and protozoa. While viruses are often discussed alongside microorganisms, they are not technically considered organisms since they require a host to reproduce. Microorganisms are the oldest and most abundant life forms on Earth. They have co-evolved with other life forms, such as animals, plants, and fungi, and thanks to their ability to adapt to different environments and factors, they have managed to preserve their origins. They are found almost everywhere – from the deep sea to animal intestines and plant root systems. Despite their microscopic size, they play a significant role in the Earth’s ecosystem.
DECOMPOSERS IN NUTRIENT CYCLES
One of the most essential roles of microorganisms is their role in the different nutrient cycles. They are crucial for decomposing organic matter and releasing essential nutrients into the soil. For example, bacteria, protozoa and some fungi break down dead plant and animal material, converting it into carbon, water and nutrients such as nitrogen and phosphorus. These substances are then available for plants to absorb, and the nutrients are passed on to animals, completing the cycle. Bacteria and fungi are also crucial for sequestering and storing carbon in the soil, which is important for improving soil quality for agriculture and also affects and mitigates climate change.
It is primarily those microbes that ensure the circulation of elements in the soil, enabling the formation of soil and humus for plant growth. Soil, which is the uppermost layer of the ground, typically extends to a depth of about 1-2 meters(3-6 feet), while humus refers to the topmost layer. Soils are influenced by the mineral composition of different rock types, water, climate, plants, bacteria, fungi, and animals living in and on the soil surface. In addition to decomposing organic matter, fungi can also break down rocks to release minerals into the soil.
SYMBIOTIC RELATIONSHIPS
Microorganisms also form symbiotic relationships with different organisms. A well-known example is mycorrhizal fungi, which live in symbiosis with plant roots. The fungi help the plants take up water and nutrients, especially phosphorus, while they obtain carbohydrates from the plant. This symbiosis is essential for plant growth and survival.
Other microorganisms live in symbiosis with humans. For example, the gut flora in the intestines includes several bacteria that the body relies on to break down food in the gastrointestinal tract. Some of these bacteria also produce essential vitamins.
NITROGEN FIXATION
Another example of a critical symbiotic relationship is the nitrogen-fixating bacteria Rhizobium, which lives in symbiosis with legumes in their root nodules. They convert nitrogen (N2) from air into ammonium or nitrate, which they supply to the plant and receive back as carbohydrates. This process makes legumes self-sufficient and rich in nitrogen, a crucial function as nitrogen is necessary for plant growth. In contrast, most plants cannot directly utilize nitrogen from the atmosphere. However, legumes like clover are often planted as intercrops to boost soil nitrogen levels, acting as natural fertilizer when the soil is tilled in the following season.
ECOLOGICAL BALANCE
Balance is crucial to the health of the entire ecosystem. Microorganisms play a key role in maintaining this balance by regulating the populations of other organisms. For example, they can act as pathogens and parasites, helping to keep animal and plant populations in check. At the same time, some microorganisms serve as biological controls by outcompeting or preventing the growth of harmful microbes.
CHANGES AND ADAPTATION
Microorganisms are highly adaptable to environmental changes, which makes them valuable bioindicators of ecosystem health. They can respond quickly to changes in pH, temperature or nutrient content, which can affect the whole ecosystem. In addition, their activity can contribute to long-term changes in soil composition by affecting soil pH or nutrient content, with consequences for all those living in and off the soil. For example, pH determines how well plants take up nutrients, as acidic soil makes uptake more difficult.
HUMAN IMPACT
Finally, human activities, such as agriculture and industry, affect the composition and functioning of microorganisms in ecosystems. For example, overuse of antibiotics can lead to resistant strains of bacteria, while pollution can alter microbial communities and their functions.
Understanding the role of microorganisms could play a key role in efforts to protect and maintain the health and functioning of ecosystems.
Microorganisms are the unsung heroes of ecosystem stability and function. They quietly support life cycles, boost plant growth, and maintain ecological balance through their diverse and complex roles. Though their work often goes unnoticed, life on Earth would be impossible without them—a powerful reminder that the unseen is no less real.
Sources
The Royal Horticultural Society.org.uk – No Dig Gardening 
Livsmedelsverket – Beneficial microorganisms
Lunds universitet – Signalling between plants and microorganisms
Goodreads.com – Marcus Rosenlund (2022) – Det stora lilla livet
ScienceDirect – Microorganism
Stockholms universitet – Microorganisms are the solution to capture carbon in soil
November2024, TÄNKOM | Revised January 2025, RETHINK
