A decomposer is an organism that breaks down complex organic matter from dead or decaying organisms to obtain energy.
It may sound unpleasant, but decomposers do nature’s dirty work. They eliminate dead or dying organisms, and while doing so, they release nutrients into the soil.
In other words, decomposers play a very crucial role in our ecosystem by recycling nutrients to keep other organisms alive.
Usually, when animals die, scavengers like hyenas or vultures consume larger portions of the body. However, they do not completely break down dead animals. Decomposers reduce dead animals (as well as plants and feces) into chemicals such as carbon and nitrogen. These chemicals gradually become part of the soil, and then those nutrients are consumed by living plants and animals that eat them.
The three major types of decomposers are:
- Fungi: release chemicals externally to break down organic matter that would otherwise not be recycled. They break down dead animals and plants into simpler substances.
- Bacteria: are microscopic organisms that live on dead materials and break them down into nutrients. The nutrients eventually get added back to the soil and water, so other living organisms can use them to grow and reproduce.
- Protozoa: are single-celled microscopic animals that feed on other microorganisms or organic tissues and debris. As predators, they prey upon microfungi, bacterial, and unicellular algae.
While no two organisms decompose in the same manner, they all undergo similar sequential phases of decomposition. To better explain this process, we have featured some of the best examples of decomposers that live in different ecosystems.
The fruiting body of mushrooms
Mushrooms are heterotrophs, which means they break down dead or decaying organic matter to make their own food.
Most people are familiar with the fruity body of the mushroom. It’s just a small part of a much larger underground network of tiny root-like structures called hyphae. The large underground network is known as mycelium.
Hyphae extend into the soil, breaking down and extracting nutrients from biomass. This makes it easier for plants to access these nutrients.
While most mushrooms expand overnight, some grow at slow rates and add tissue to their fruiting bodies by inserting hyphae.
Saprobes/wood decomposers | Image credit: Wikimedia
Saprobes are the most common type of fungi that feed on dead or decaying leaves, litter, wood, and other organic matter. They secrete enzymes to break down these complex matter into simpler substances.
More specifically, saprobes break down matter into its composites:
- Lipids are broken down into fatty acids and glycerol
- Proteins are broken down into their amino acid composites
- Cellulose is broken down into glucose
- Starch is broken down into disaccharides
Other organisms use these vital nutrients to grow and reproduce.
Many saprobes are too small to see with the naked eye, while some produce stalked mushrooms that grow on wood and soil.
7. Grass Bacillus
Transmission electron microscopic image of Grass Bacillus
Grass Bacillus are rod-shaped anaerobic bacteria widely found in water and soil. They can form a hard, protective endospore, which enables them to tolerate harsh environmental conditions.
Grass Bacillus primarily contains two enzymes:
- Catalase KatA and MrgA: facilitates the decomposition of hydrogen peroxide to water and oxygen
- Superoxide dismutase: catalyzes the breakdown of superoxide into oxygen and hydrogen peroxide
Some strains of Bacillus bacteria are harmful to plants, humans, and other organisms. B. cereus, for example, often causes spoilage of canned food and food poisoning for a short duration. It is also used to produce medically useful antibiotics.
6. Pseudomonas fluorescens
Pseudomonas fluorescens visualized under white light
Pseudomonas fluorescens is a rod-shaped bacterium that requires oxygen to grow, but certain strains can use nitrate instead of oxygen during cellular respiration. They grow best at temperatures between 25 and 30°C.
Pseudomonas fluorescens produces heat-stable enzymes, such as lipases and proteases. These enzymes spoil milk by breaking down casein (the main protein in the milk) and causing bitterness.
These bacteria are commonly found in soil and water bodies. While they break down dead organic matter, they are also capable of compromising the human immune system, creating rare disease conditions.
This type of bacteria has also been found to be useful in treating eye, ear, and skin disorders. It is also used in the production of various medical creams, ointments, and sprays.
Molds on a Petri dish
Type: Microscopic fungus
There are thousands of species of molds that live on plant and animal matter. Some live in aquatic environments, but most of them require moist conditions for growth.
Molds secrete hydrolytic enzymes to break down complex biopolymers (like cellulose and starch) into simpler substances. Some molds synthesize siderophores and mycotoxins along with lytic enzymes, inhibiting the growth of competing microorganisms.
Molds can multiply by generating microscopic spores (similar to the seeds created by plants). Since these spores are very small, they can easily float through the air and travel greater distances. Some molds can also grow on stored food, making it uneatable or toxic.
Yeast on grapes
Although we use yeast for baking and making beverages, in nature, yeast acts as a great decomposer. It plays a crucial role in the decomposition of plant materials, actively participating as a producer of hydrolytic enzymes.
There are more than 1,500 known species of yeast. Most of them occur on the skins of tree bark, rotting wood, leaf litter, and fruits and berries, such as apples, peaches, and grapes. Some are found in association with insects and soil.
Yeast can survive in the absence and presence of oxygen. In the lack of oxygen, they undergo fermentation and transform carbohydrates (sugar source) into carbon dioxide and alcohol. In the presence of oxygen, they undergo aerobic respiration and transform carbohydrates into carbon dioxide and water. Furthermore, they grow best in a neutral and slightly acidic pH environment.
What are they: Single-celled organisms that feed primarily on bacteria, soluble organic matter, other protozoa, and sometimes fungi
Protozoans inhabit a wide range of habitats, both terrestrial and aquatic. Most are free-living, while some carry out a life cycle within a host. During the feeding and growth part of their life cycle, protozoans are called trophozoites.
They feed on small particulate food sources, like bacteria, and are responsible for regulating the population of bacteria.
When protozoans are in the form of trophozoites, they eat bacteria that have higher concentrations of nitrogen. They release this excess nitrogen in the form of ammonium. Other organisms rapidly take up most of the ammonium, and some is utilized by plant matter.
This is how protozoa play a crucial role in mineralizing nutrients, making them available for use by plants and soil organisms.
Psychrophiles are cold-tolerant bacteria that have the ability to grow and reproduce at low temperatures ranging between -20 °C and 15°C. They are commonly found in deep ocean water and polar regions.
They play a significant role in the biodegradation process as various autochthonous microorganisms have been found to possess the ability to degrade aliphatic and aromatic hydrocarbons at freezing temperatures.
Some studies show that the psychrophilic bacteria isolated from soil can decompose urea. Because of their unique biological characteristics, psychrophiles can be exploited in biotechnological industries such as enzyme production, pharmaceutical, and bioremediation.
Aerobic mesophilic bacteria | Image credit: ResearchGate
Mesophiles are tiny organisms that grow in a moderate environment. Unlike thermophiles, which can live at temperatures as high as 80°C, mesophiles grow best at temperatures between 20°C and 45°C.
Different types of microorganisms predominate in different composting phases. For example, initial decomposition is carried by mesophiles, which quickly degrade the soluble matter. The heat produced during this degradation process rapidly increases the temperature of the compost.
As temperature increases above 40°C, the mesophilic organisms become less effective and are gradually replaced by other microorganisms like thermophiles.
Mesophiles commonly occur in dairy products like yogurt and cheese. Sometimes, they are included during the fermentation of beer and winemaking. And since these organisms thrive at normal human body temperature (37°C), most of the human pathogens are mesophiles.
Frequently Asked Questions
What is the difference between a decomposer and a detritivore?
The terms detritivore and decomposer are often used interchangeably, but they are very different from each other. While decomposers directly absorb nutrients through external biological or chemical processes, detritivores ingest and digest dead organic materials internally.
|Absorbs nutrients from dead or decaying matter through external chemical and biological processes||Feed orally on the dead organic matter to get nutrients and energy|
|Examples include fungi and bacteria||Examples include earthworms and woodlice|
Why are decomposers essential to a healthy food web and ecosystem?
Not everything in the food chain gets eaten. Most animals and plants die long before they become anyone else’s food. That’s where decomposers play their role. They break down deal plants, animals, and waste of other organisms.
More importantly, decomposers make vital nutrients available to the ecosystem’s primary producers, such as plants and algae. They convert complex organic matter into simpler compounds like water and carbon dioxide, and compounds containing calcium, phosphorus, and nitrogen. These compounds are consumed by soil organisms and plants, which are then consumed by ground animals.
You can say that decomposers help in maintaining the flow of energy through an ecosystem.
How humans use decomposers?
For centuries, humans have found ways for decomposers to work in our favor. Yeast, for example, is extensively used for baking bread and bakery products. Bacteria are used in the fermentation of cheese, yogurt, and sour cream.
Researchers have also found a way to utilize certain decomposers in wastewater treatment plants, harness bacteria for bioremediation, and clean up environmental damage such as chemical spills caused by people.