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Photoautotrophs are organisms that can utilize light energy from sunlight and elements (such as carbon) from inorganic compounds to produce organic materials needed to sustain their own metabolism (i.e. autotrophy).
Photoautotrophs are capable of synthesizing their own food from inorganic substances using light as an energy source. Green plants and photosynthetic bacteria are photoautotrophs. Photoautotrophic organisms are sometimes referred to as holophytic .
Photoautotrophs evolved from heterotrophic bacteria by developing photosynthesis. The earliest photosynthetic bacteria used hydrogen sulphide . Due to the scarcity of hydrogen sulphide, some photosynthetic bacteria evolved to use water in photosynthesis, leading to cyanobacteria .
These include photoautotrophs (which use sunlight) and lithoautotrophs (which use inorganic oxidation). Heterotrophs, such as animals and fungi, are not capable of carbon fixation but are able to grow by consuming the carbon fixed by autotrophs or other heterotrophs. Seven natural autotrophic carbon fixation pathways are currently known.
Organotrophs use organic compounds as electron/hydrogen donors. Lithotrophs use inorganic compounds as electron/hydrogen donors.. The electrons or hydrogen atoms from reducing equivalents (electron donors) are needed by both phototrophs and chemotrophs in reduction-oxidation reactions that transfer energy in the anabolic processes of ATP synthesis (in heterotrophs) or biosynthesis (in autotrophs).
Aerobic anoxygenic phototrophic bacteria are divided into two genera. There are two marine (Erythrobacter and Roseobacter) and six freshwater (Acidiphilium, Erythromicrobium, Blastomonas (synonym: Erythromonas), Porphyrobacter, Roseococcus, and Sandaracinobacter) genera of these bacteria. [3]
Green sulfur bacteria are photoautotrophs: they not only get energy from light, they can grow using carbon dioxide as their sole source of carbon. They fix carbon dioxide using the reverse tricarboxylic acid cycle (rTCA) cycle [ 9 ] where energy is consumed to reduce carbon dioxide, rather than oxidize as seen in the forward TCA cycle , [ 9 ...
Photoheterotrophs generate ATP using light, in one of two ways: [6] [7] they use a bacteriochlorophyll-based reaction center, or they use a bacteriorhodopsin.The chlorophyll-based mechanism is similar to that used in photosynthesis, where light excites the molecules in a reaction center and causes a flow of electrons through an electron transport chain (ETS).