Fundamentals of Microbiology

4.1.3 Mutualism

An obligatory association that provides some reciprocal benefit to both partners . For example: Lichens-an association between a fungus (ascomycetes) and an alga (green algae) or cyanobacterium, Fungal partner (mycobiont) obtains nutrients from alga by hyphal projections that penetrate the algal cell wall as well as oxygen for respiration. Algal partner (phycobiont) is protected from excess light intensity and is provided with water, minerals, and a firm substratum in which it can grow protected from environmental stress.

Endosymbiotic chemolithotrophic bacteria provide the main energy source in the community through the oxidation of hydrogen sulfide. The endosymbiotic bacteria are maintained in specialized cells (trophosome) of the tube worm. The tube worm binds hydrogen sulfide to hemoglobin and transports it to the bacteria; the bacteria use the energy from hydrogen sulfide oxidation to synthesize reduced organic material that is supplied to the tube worm.