Rhodopseudomonas palustris

Rhodopseudomonas palustris is a rod-shaped gram-negative purple non-sulfur bacterium, notable for its ability to switch between four different modes of metabolism. R. palustris is found extensively in nature and has been isolated from swine waste lagoons, earthworm droppings, marine coastal sediments and pond water. Although purple non-sulfur bacteria are normally photoheterotrophic, R. palustris can flexibly switch among any of the four modes of metabolism that support life: photoautotrophic, photoheterotrophic, chemoautotrophic and chemoheterotrophic. R. palustris is usually found as a wad of slimy masses and cultures appear from pale brown to peach-colored. Etymologically, rhodum is a Greek noun meaning rose, pseudes is the Greek adjective for false and monas refers to a unit in Greek. Therefore, Rhodopseudomonas, which implies a unit of false rose, describes the appearance of the bacteria. Palustris is Latin for marshy, and indicates the common habitat of the bacterium. R. palustris can grow with or without oxygen, or it can use light, inorganic or organic compounds for energy. It can also acquire carbon from either carbon dioxide fixation or green plant-derived compounds. Finally, R. palustris is also capable of fixing nitrogen for growth. This metabolic versatility has raised interest in the research community, and it makes this bacterium suitable for potential use in biotechnological applications. Efforts are currently being made to understand how this organism adjusts its metabolism in response to environmental changes. The complete genome of the strain Rhodopseudomonas palustris CGA009 was sequenced in 2004 (see list of sequenced bacterial genomes) to get more information about how the bacterium senses environmental changes and regulates its metabolic pathways. It was found that R. palustris can deftly acquire and process various components from its environment, as necessitated by fluctuations in the levels of carbon, nitrogen, oxygen and light. R. palustris has genes that encode for proteins that make up light-harvesting complexes and photosynthetic reaction centres. LH complexes and photosynthetic reaction centers are typically found in photosynthetic organisms like green plants. Moreover, R. palustris can modulate photosynthesis according to the amount of light available, like other purple bacteria. For instance, in low-light circumstances, it responds by increasing the level of these LH complexes that allow light absorption. However, the wavelengths of the light absorbed by R. palustris differ from those absorbed by other phototrophs. R. palustris also has genes that encode for the protein ruBisCO, an enzyme that is necessary for carbon dioxide fixation in plants and other photosynthetic organisms. The genome of CGA009 also reveals the existence of proteins involved in nitrogen fixation (see diazotroph).