Mutualism:

Mutualism is the way of two or different microbial interactions biologically where every microbe benefits from the relationship. Both are mutually dependent on each other; host is metabolically dependant. When the interaction takes place within the species it is referred to as co-operation. For instance the microbial interaction between cows and bacteria is mutualism. Cow is benefitted from the bacteria by the production of cellulase. This cellulase helps in digestion by supplying proper nutrients.

Types of mutual relationship: Three type of mutual relationship are as below.

• Resource- resource relationship
• Service- relation relationship
• Service- service relationship

Mutualism Instance:

The classic instance of mutual relationship is protozoan and termite interaction. Protozoa is having flagellum which lives in the termite guts and wood roaches. Host flagellate will appear when carbohydrate is in diet. They are utilized as cellulose resource and host ingest the carbohydrate resource. Protozoa digest wood roaches utilize this carbohydrate source cellulose and form metabolic products like acetate and similar products. The interaction is possible as host is not capable of producing cellulase enzyme (the enzyme helps in hydrolysis of cellulose). It is for this reason protozoa is mutually dependent on the termite.

Lichens:

Best instance of mutualism is lichens, where there is mutual interaction between fungi namely ascomycetes referred as mycobiont and genera of algae like blue algae and bacteria like cyanobacteria referred as phycobiont. Phycobiont depends on light, CO₂ and other nutrients. The lichen characteristic structure is mutually dependent and it is not characterized as symbiont.