The following points highlight photoautotrophs and chemoautotrophs types of microorganisms that are based upon the source of electron.
Type # 1. Photoautotrophs:
Photoautotrophs include the photosynthetic bacteria, algae and green plants. These organisms fix carbon utilizing the energy of solar radiations through a process called photosynthesis.
They are also called the primary producers of simple procedures because such organisms are capable of self production of organic material from simple inorganic sources (sunlight for energy and carbon dioxide for carbon). Photoautotrophs form the first trophic (food) level in any food chain. These organisms have a very simple food requirements and can grow on very simple defined media (where chemical composition is known).
Photoautotrophs are the organisms which require solar radiations for their energy but depend upon readymade carbon source in the form of organic compounds. These include green non-sulfur bacteria and purple non-sulfur bacteria.
Type # 2. Chemoautotrophs:
Chemoautotrophs utilize the energy present in chemical compounds and carbon in the form of carbon dioxide. These include organisms like Beggiatoa (utilizing hydrogen sulfide as energy source), Nitrosomonas (utilizing ammonia as energy source), Thiobacillus (utilizing iron), Nitrobacter (utilizing nitrites) etc.
These organisms also have simpler nutritional requirements and can be grown on defined media. Generally, same organic compound can act both as a source of energy as well as carbon. These organisms are the chief concern to man because all the parasites or pathogens of man, animals and plants are chemo heterotrophs. Apart from pathogens all the saprophytes are also chemoheterotrophic.