ALSO referred to as blue-green algae despite the fact of being distinct from algae.Many lichen partners include one photobiont and one MYCOBIONT which is not universal and there are lichens with more than one photobiont partner. The species of Ascomycetes or Basidiomycetes are the most common fungi in lichens. The common algal partners are either the green algae Chlorophyta or Cyanophyceae family of blue-green bacteria.Mostly, lichens grow slowly. The one in which the phycobiont is a blue-green bacterium that has the ability to convert nitrogen gas into AMMONIA. Some can reach the age of many centuries, mainly the ones living in stressful environments such as the arctic tundra or alpine. Protozoa is an informal term for a group of single-celled eukaryotes, either free-living or PARASITIC, that feed on organic matter such as other microorganisms or organic tissues and debris.A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism.Viruses infect all types of life forms, from ANIMALS and plants to microorganisms, including bacteria and archaea.Bacteria are a type of biological cell.They constitute a large domain of prokaryotic microorganisms.Bacteria were among the first life forms to appear on Earth, and are present in most of its habitats.