An organotroph is an organism that obtains hydrogen or electrons from organic substrates. This term is used in microbiology to classify and describe organisms based on how they obtain electrons for their respiration processes. Some organotrophs such as animals and many bacteria, are also heterotrophs. Organotrophs can be either anaerobic or aerobic.
Organisms that are not phototrophic capture energy from other sources, specifically by transforming thermodynamically unstable molecules into more stable species. Such organisms are known generically as chemotrophs. They can be divided into various groups, depending upon the types of food molecules (energy sources) they use: these include organotrophs, which use carbon-containing molecules (you yourself are an organotroph) and lithotrophs or rock eaters, which use various inorganic molecules. In the case of organisms that can “eat” H2, the electrons that result are delivered, along with accompanying H+ ions, to CO2 to form methane (CH4) following the reaction:
CO2 + 4H2 ⇌ CH4 + 2H2O.
Such organisms are referred to as methanogens (methane-producers)181. In the modern world methanogens (typically archaea) are found in environments with low levels of O2, such as your gut. In many cases reactions of this type can occur only in the absence of O2. In fact O2 is so reactive, that it can be thought of as a poison, particularly for organisms that cannot actively “detoxify” it. When we think about the origins and subsequent evolution of life, we have to consider how organisms that originally arose in the absence of molecular O2 adapted as significant levels of O2 began to appear in their environment. It is commonly assumed that modern strict obligate anaerobes might still have features common to the earliest organisms.
The amount of energy that an organism can capture is determined by the energy of the electrons that the electron acceptor(s) they employ can accept. If only electrons with high amounts of energy can be captured, which is often the case, then inevitably large amounts of energy are left behind. On the other hand, the lower the amount of energy that an electron acceptor can accept, the more energy can be extracted and captured from the original “food” molecules and the less energy is left behind. Molecular oxygen is unique in its ability to accept low energy electrons. For example, consider an organotroph that eats carbohydrates (molecules of the general composition [C6H10O5]n), a class of molecules that includes sugars, starches, and wood, a process known as glycolysis, from the Greek words meaning sweet (glyco) and splitting (lysis). In the absence of O2, that is under anaerobic conditions, the end product of the breakdown of a carbohydrate leaves ~94% of the theoretical amount of energy present in the original carbohydrate molecule remaining in molecules that cannot be broken down further, at least by most organisms. These are molecules such as ethanol (C2H6O). However, when O2 is present, carbohydrates can be broken down more completely into CO2 and H2O, a process known as respriration. In such O2 using (aerobic) organisms, the energy released by the formation of CO2 and H2O is stored in energetic electrons and used to generate a membrane-associated H+ based electrochemical gradient that in turn drives ATP synthesis, through a membrane-based ATP synthase. In an environment that contains molecular oxygen, organisms that can use O2 as an electron acceptor have a distinct advantage; instead of secreting energy rich molecules, like ethanol, they release the energy poor (stable) molecules CO2 and H2O.
No matter how cells (and organisms) capture energy, to maintain themselves and to grow, they must make a wide array of various complex molecules. Understanding how these molecules are synthesized lies within the purview of biochemistry. That said, in each case, thermodynamically unstable molecules (like lipids, proteins, and nucleic acids) are built through series of coupled reactions that rely on energy capture from light or the break down of food molecules.
As nouns the difference between heterotroph and organotroph
is that heterotroph is (ecology) an organism which requires an external supply of energy in the form of food as it cannot synthesize its own while organotroph is (biology) an organism that obtains its energy from organic compounds.
Organic compounds that are used as electron donor are called Organotrophs . An organotroph organism obtains hydrogen or electrons from organic substrates. This term is mostly used in microbiology to classify and describe organisms based on how they obtain electrons for their respiration processes. Some organotrophs such as animals and many bacteria, are also heterotrophs. Organotrophs can be either anaerobic or aerobic.
Electron Donors and Acceptors
- Organisms that use organic molecules as an energy source are called organotrophs.
- Organotrophs (animals, fungi, protists) and phototrophs (plants and algae) constitute the vast majority of all familiar life forms.
- Because of their volume of distribution, lithotrophs may actually out number organotrophs and phototrophs in our biosphere.
- Just as there are a number of different electron donors (organic matter in organotrophs, inorganic matter in lithotrophs), there are a number of different electron acceptors, both organic and inorganic.
Electron Donors and Acceptors in Anaerobic Respiration
- Sulfate reduction requires the use of electron donors, such as the carbon compounds lactate and pyruvate (organotrophic reducers), or hydrogen gas (lithotrophic reducers).
Sulfate and Sulfur Reduction
- Many sulfate reducers are organotrophic, using carbon compounds, such as lactate and pyruvate (among many others) as electron donors, while others are lithotrophic, and use hydrogen gas (H2) as an electron donor.
Types of Catabolism
- Organic molecules are used as a source of energy by organotrophs, while lithotrophs use inorganic substrates and phototrophs capture sunlight as chemical energy.
Nongenetic Categories for Medicine and Ecology
- Chemoorganoheterotrophs (or organotrophs) exploit reduced-carbon compounds as energy sources, such as carbohydrates, fats, and proteins from plants and animals.