What is the Difference Between Mutualism and Protocooperation

The key difference between mutualism and protocooperation is that mutualism is an obligatory microbial interaction where mutualist and host are metabolically dependent on each other, whereas protocooperation is a non-obligatory microbial interaction where mutualist and host are not metabolically dependent on each other.

Microorganisms can physically associate with other microorganisms in a variety of ways. These microbial interactions are very important for their survival. In these interactions, one organism can be present on the surface of another as an ectobiont, or one organism can be present within another organism as an endobiont. Microbial interactions can be positive such as mutualism, protocooperation, and commensalism or negative such as parasitism, predation and competition. Mutualism and protocooperation are two positive microbial interactions.

CONTENTS

1. Overview and Key Difference
2. What is Mutualism 
3. What is Protocooperation
4. Similarities – Mutualism and Protocooperation
5. Mutualism vs Protocooperation in Tabular Form
6. Summary

What is Mutualism?

Mutualism is an obligatory microbial interaction where the mutualist and host are metabolically dependent on each other. It is defined as a relationship where each organism in the interaction gets benefits from the association. Mutualism is a very specific relationship. Therefore, one member of the association cannot be replaced by another species. This specific microbial relationship requires close physical contact between interacting organisms. Moreover, mutualism is such a relationship that allows organisms to exist in habitats that cannot be occupied by either species alone. The organisms in mutualism act as a single organism.

Lichens are an excellent example of mutualism. They are an association of specific fungi with algae or cyanobacteria. Lichens are composite organisms.  In a lichen, the fungal partner is called a mycobiont. Fungi provide protection for algae or cyanobacteria. The algal or cyanobacterial partner is termed phycobiont. The phycobionts are usually photoautotrophs. Therefore, fungi get their organic carbon directly from algal or cyanobacterial partners. Furthermore, protozoans and termites also have a mutualistic interaction. Protozoans normally live in the gut of termite and feed on carbohydrates it acquires from the host termite. The protozoan is metabolized food into acetic acid. Termite utilizes this acetic acid.

What is Protocooperation?

Protocooperation is a non-obligatory microbial interaction where the mutualist and host are not metabolically dependent on each other. It is defined as a relationship where organisms in the association are mutually benefited from each other but do not depend on each other. It is not at all necessary for protocooperation to occur. Even growth and survival are possible in the absence of interaction. Therefore, organisms in protocooperation purely interact with each other for the gain that they receive from the relationship.

Lactobacillus delbrueckii ssp bulgaricus and streptococcus thermophilus have protocooperation. They are starter bacteria commonly used in yogurt cultures. Streptococcus thermophilus produces pyruvic acid, formic acid, folic acid, ornithine, long chain fatty acids, and CO₂ that stimulates the growth of Lactobacillus bulgaricus. On the other hand, Lactobacillus bulgaricus produces peptides, free amino acids, and putrescine through proteolysis, which stimulate the growth of Streptococcus thermophilus. Furthermore, the association of desulfovibrio and chromatium bacteria, the interaction between N₂ fixing bacteria and cellulolytic bacteria (cellulomonas) are also recognized as protocooperation.

What are the Similarities Between Mutualism and Protocooperation?

• Mutualism and protocooperation are two positive microbial interactions.
• They are both ecological interactions.
• In both microbial interactions, each organism in the interaction gets benefits from the association.
• Both interactions are very important for the ecosystem.

What is the Difference Between Mutualism and Protocooperation?

Mutualism is an obligatory microbial interaction where mutualist and host are metabolically dependent on each other, while protocooperation is a non-obligatory microbial interaction where mutualist and host are not metabolically dependent on each other. So, this is the key difference between mutualism and protocooperation. Furthermore, in mutualism, the cooperating species depend on each other for survival, whereas in protocooperation, the cooperating species do not depend on each other for survival.

The following infographic lists the differences between mutualism and protocooperation in tabular form for side by side comparison.

Summary – Mutualism vs Protocooperation

Microorganisms can interact with each other for various reasons. Mutualism and protocooperation are two positive microbial interactions. Mutualism is an obligatory microbial interaction where mutualist and host are metabolically dependent on each other. Protocooperation is a non-obligatory microbial interaction where mutualist and host are not metabolically dependent on each other. Thus, this is the key difference between mutualism and protocooperation.

Reference:

1. Karki, Gaurab. “Microbial Interaction and Types (Mutualism, Syntropism, Proto-Cooperation, Commensalism, Antagonism, Parasitism, Predation, Competition).” Online Biology Notes, 18 Dec. 2018.
2. Doty, Lewis. “Cattle Rumen Role – MICROORGANISM INTERACTIONS.” Ecology Center, 4 June 2021.

Image Courtesy:

1. “Flavoparmelia caperata – lichen – Caperatflechte” By Norbert Nagel, Mörfelden-Walldorf, Germany – Own work (CC BY-SA 3.0) via Commons Wikimedia

2. “Lactobacillus bulgaricus” By Gengiskanhg assumed – No machine-readable source provided. Own work assumed (based on copyright claims). (CC BY-SA 3.0) via Commons Wikimedia