Opsin three domains of life: Archaea, Bacteria, and Eukaryota. In Eukaryota, type I opsins are found mainly in unicellular organisms such as green algae, and in fungi. In most complex multicellular eukaryotes, type I opsins have been replaced with other light-sensitive molecules such as cryptochrome and phytochrome in plants, and type II opsins in Metazoa (animals). Microbial opsins are often known by the rhodopsin form of the molecule, i.e., rhodopsin (in the broad sense) = opsin + chromophore. Among the many kinds of microbial opsins are the proton pumps bacteriorhodopsin (BR) and xanthorhodopsin (xR), the chloride pump halorhodopsin (HR) the photosensors
Exogenous bacteria of this concept is "bacterial flora," which consists of exogenous bacteria ingested and endogenously colonized during the early stages of life. Bacteria that are part of normal internal ecosystems, also known as bacterial flora, are called "Endogenous Bacteria". A significant amount of prominent diseases are induced by "exogenous bacteria" such as "gonorrhea", "meningitis", "tetanus", and "syphilis." Pathogenic exogenous bacteria can enter a host via cutaneous transmission, inhalation, and consumption. Only a minority of bacteria species cause disease in humans; and many species colonize in the human body to create an ecosystem known as bacterial flora. Bacterial flora is endogenous bacteria,