WHAT IS TROPHIC MUTUALISM? (WITH EXAMPLES) - BIOLOGY - 2025

The trophic mutualism or sintrofismo is an interaction between organisms of different species in which both cooperate for obtaining or degradation of nutrients and mineral ions. The interaction represents the exchange of nutrients between species.

Generally, the members of the relationship are an autotrophic and a heterotrophic organism. There are cases of both compulsory and optional mutualism.

Source: Adrian Pingstone (Arpingstone), from Wikimedia Commons

The most studied cases in nature of trophic mutualism are the interactions between nitrogen-fixing bacteria and legume plants, mycorrhizae, lichens, digestive symbionts, among others.

What is trophic mutualism?

Mutualism: relationship +, +

The organisms of a community - different species that coexist in the same time and space - are not in isolation from each other. Species interact in different ways, usually in a network of intricate patterns.

Biologists have named each of these interactions, depending on how the members of the interaction are affected. In this context, mutualism is defined as a relationship where species associate and both obtain benefits.

Types of mutualism

There is a wide diversity of mutualisms in nature. Trophic mutualism occurs when the interacting species cooperate to obtain food.

It is also known as "syntrophism", a term from the Greek roots syn which means mutual and trophe which means nutrition. In English, this interaction is known under the name of resource-resource interactions.

In addition to trophic mutualism, there are cleaning mutualisms, where species exchange cleaning services for protection or food; defensive mutualism, where the species protect themselves against possible predators, and dispersal mutualism, as in the case of animals that disperse plant seeds.

Another classification system divides mutualism into compulsory and optional. In the first case, the two organisms live very close and it is not possible for them to live without the presence of their partner.

In contrast, facultative mutualism occurs when the two members of the interaction can live without the other, under certain conditions. In nature, the two types of mutualism, compulsory and facultative, have been evidenced within the category of trophic mutualism.

Mutualism is the same as symbiosis?

The term mutualism is often used as a synonym for symbiosis. However, other relationships are also symbiotic, such as commensalism and parasitism.

A symbiosis, strictly speaking, is a close interaction between different species over a long time.

Examples of trophic mutualism

Nitrogen-fixing bacteria and legume plants

Some microorganisms have the ability to fix atmospheric nitrogen through symbiotic associations with legume plants. The main genera include Rhizobium, Azorhizobium, Allorhizobium, among others.

The relationship takes place thanks to the formation of a nodule in the root of the plant, the region where nitrogen fixation takes place.

The plant secretes a series of substances known as flavonoids. These promote the synthesis of other compounds in the bacteria that favor the association between it and root hairs.

Mycorrhizae

Mycorrhizae are associations between a fungus and the roots of a plant. Here, the plant provides the fungus with energy, in the form of carbohydrates, and it responds with protection.

The fungus increases the surface of the roots of the plant for the absorption of water, nitrogenous compounds, phosphorus, and other inorganic compounds.

With the intake of these nutrients, the plant remains healthy and allows it to grow efficiently. In the same way, the fungus is also responsible for protecting the plant from possible infections that may enter through the root.

The symbiosis of the endomycorrhiza type increases the performance of the plant against different negative factors, such as attack by pathogens, drought, extreme salinity, the presence of toxic heavy metals or other pollutants, etc.

Lichens

This term describes the association between a fungus (an ascomycete) and an alga or a cyanobacteria (blue-green algae).

The fungus surrounds the cells of its algae companion, within the fungal tissues that are unique to the association. The penetration into the cells of the alga is carried out by means of a hypha known as a haustorium.

In this association, the fungus obtains nutrients from the algae. The algae is the photosynthetic component of the association and they have the ability to produce nutrients.

The fungus offers the algae humid conditions for its development and protection against excess radiation and other disturbances, both biotic and abiotic.

When one of the members corresponds to a blue green algae, the fungus also benefits from the nitrogen fixation of its partner.

The association increases the survival of both members, however, the relationship is not necessary for the growth and reproduction of the organisms that compose them, especially in the case of algae. In fact, many symbiotic algae species can live independently.

Lichens are extremely diverse, and we find them in different sizes and colors. They are classified as foliose, crustacean and fructic lichens.

Leaf cutter ants and mushrooms

Some leafcutter ants are known to harvest certain types of fungi. The purpose of this relationship is to consume the fruiting bodies that are produced by the fungi.

The ants take plant matter, such as leaves or flower petals, cut them into pieces and there they plant portions of the mycelium. The ants build a kind of garden, where they later consume the fruits of their labor.

Symbionts in ruminants

The staple food of ruminants, grass, contains high amounts of cellulose, a molecule that consumers are not able to digest.

The presence of microorganisms (bacteria, fungi and protozoa) in the digestive system of these mammals allows the digestion of cellulose, since they convert it into a variety of organic acids. Acids can be used by ruminants as a source of energy.

There is no way that ruminants can consume grass and digest it efficiently without the presence of the aforementioned organisms.

References

1. Parga, ME, & Romero, RC (2013). Ecology: impact of current environmental problems on health and the environment. Ecoe Editions.
2. Patil, U., Kulkarni, JS, & Chincholkar, SB (2008). Foundations in Microbiology. Nirali Prakashan, Pune.
3. Poole, P., Ramachandran, V., & Terpolilli, J. (2018). Rhizobia: from saprophytes to endosymbionts. Nature Reviews Microbiology, 16 (5), 291.
4. Sadava, D., & Purves, WH (2009). Life: The Science of Biology. Panamerican Medical Ed.
5. Singh, DP, Singh, HB, & Prabha, R. (Eds.). (2017). Plant-Microbe Interactions in Agro-Ecological Perspectives: Volume 2: Microbial Interactions and Agro-Ecological Impacts. Springer.
6. Somasegaran, P., & Hoben, HJ (2012). Handbook for rhizobia: methods in legume-Rhizobium technology. Springer Science & Business Media.
7. Wang, Q., Liu, J., & Zhu, H. (2018). Genetic and Molecular Mechanisms Underlying Symbiotic Specificity in Legume-Rhizobium Interactions. Frontiers in plant science, 9, 313.