Plant-Microorganism Interactions Lichen consisting of two organisms: a fungus and an alga: Algae or cyanobacteria grow phototrophically and provide nutrient for the fungus, which offers a firm anchor and inorganic nutrient for the alga algae.Plant-Microorganism Interactions Lichen consisting of two organisms: a fungus and an alga: Algae or cyanobacteria grow phototrophically and provide nutrient for the fungus, which offers a firm anchor and inorganic nutrient for the algae