Metabolic diversity and individual adaptability
The international technical term for this lemma is Primary nutritional groups in German: metabolic diversity and individual adaptability .
The energy metabolism of animals and plants shows fundamental differences. Plants carry out photosynthesis , while animals get their energy from food , which is "burned" in the respiratory chain . This difference is based on very different metabolic pathways . Even greater differences become apparent when one looks at all living things, not just eukaryotes (which include animals and plants), but also prokaryotes ( bacteria and archaetes ). There are metabolic types that enable organisms to grow even in biotopes where plant and animal life is not possible.
| Redox reaction | E ' 0 (V) |
|---|---|
| CO + H 2 O → CO 2 + 2H + + 2 e - | −0.54 |
| H 2 → 2H + + 2 e - | −0.41 |
| Ferredoxin reduced → Ferredoxin oxidized + e - | −0.4 |
| NADPH + H + → NADP + + 2 e - + 2 H + | −0.32 |
| H 2 S → S + 2H + + 2 e - | −0.25 |
| S + 4 H 2 O → SO 4 2− + 8 H + + 8 e - | −0.23 |
| NO 2 - + H 2 O → NO 3 - + 2 H + + 2 e - | +0.42 |
| NH 4 + + 2 H 2 O → NO 2 - + 8 H + + 6 e - | +0.44 |
| Fe 2+ → Fe 3+ + e - | +0.78 |
| 2 H 2 O → O 2 + 4 H + + 4 e - | +0.86 |
| Tabular overview of the metabolic types of microorganisms | |||||
|---|---|---|---|---|---|
| function | Alternatives | Designation of the metabolic type | |||
|
Energy source for
Regeneration of ATP |
light | photo- | -trophe aerobes / anaerobes (with / without O 2 as e - acceptor ) |
||
| Redox reaction | chemo- | ||||
| electrical current | electrical | ||||
| Electron donor for biosynthesis | inorganic substances | litho- | |||
| organic compounds | organo- | ||||
| Source of carbon for biosynthesis | CO 2 | automobile- | |||
| organic compounds | hetero- | ||||
Overview
The characterization of a metabolic type results from the combination of the above terms. Example: Organisms have a chemo-litho-autotrophic metabolism that obtain ATP through chemical reactions and get along with inorganic electron donors and CO 2 during their biosynthesis . Humans have a chemo-organo-heterotrophic , short heterotrophic metabolism.
Profound metabolic differences are also responsible for whether an organism needs atmospheric oxygen (O 2 ) to survive or whether it is inhibited or killed by it.
- Aerobic organisms require oxygen for breathing ( respiratory chain ).
- Anaerobes live in biotopes without oxygen. Many of them can onlygrow in thestrict absence of O 2 and are obligately anaerobic . Such organisms also have unique metabolic pathways ( anaerobic respiration ).
Disambiguation
There are organisms that have various metabolic pathways available and, for example, can grow phototrophically in light, otherwise chemotrophically.
Such growth is called mixotrophic when organisms can use dichotomous metabolic pathways (photo / chemo, litho / organo, auto / hetero) at the same time .
Energy metabolism
All known living things need a source of energy to regenerate adenosine triphosphate (ATP) from ADP . The ATP then provides the energy for building biomass.
- Chemotrophic organisms use the chemical energy of a wide variety of substances to regenerate ATP. The chemotrophic forms of metabolism include aerobic respiration , fermentation and anaerobic respiration . Examples: animals , fungi , intestinal bacteria .
-
Phototrophic organisms obtain energy primarily through photosynthesis from light with the help of pigments , but can also use chemical energy, e.g. B. from the body's own storage materials. Examples are plants and cyanobacteria , but also a variety of phototrophic microorganisms that can often also grow anaerobically.
- A special case are radiotrophic fungi, which are chemotrophic in principle. You can also gain energy from ionizing radiation . This form of energy generation has so far only been described for a few mushrooms with the pigment melamine . The metabolic pathway is unclear.
Litho- and organotrophic, auto- and heterotrophic metabolism
-
Organotrophic organisms obtain the electron donors for the regeneration of NADPH from organic compounds. In so far as they mostly also get the carbon for biosynthesis from it, they have a heterotrophic metabolism. Since the two usually coincide, heterotroph is synonymous with the uncommon terms organotrophic and organoheterotrophic .
- There are photoheterotrophic microorganisms that get their energy from a special type of photosynthesis .
- As a rule, heterotrophic organisms get their energy from biochemical reactions, so they are also chemotrophic. In this respect, the term chemoorganoheterotroph is not common.
- Have a lithotrophic metabolism
- phototrophic organisms that regenerate NADPH from inorganic substances with the help of light. Cyanobacteria and the plant chloroplasts derived from them , which can phototrophically obtain NADPH from water ( hydrotrophy ), occupy a prominent position . Since they can convert their CO 2 into organic carbon during photosynthesis ( carbon dioxide assimilation through the Calvin cycle ), they are photo-litho- autotrophic .
- Many chemolithotrophic organisms are also autotrophic and can assimilate CO 2 ( chemolithoautotrophy ). Their carbon biosynthesis is sometimes referred to as chemosynthesis , based on photosynthesis . Many chemolithotrophic organisms use the Calvin cycle for CO 2 assimilation , while others use completely different metabolic pathways.
Conceptual and historical
Diet, carbon source
Until well into the 20th century, science divided the world of living things into two categories with regard to their diet: animals and plants. First of all, it was clear about their diet:
- Animals (along with various other living beings) are "dependent on body substances or metabolic products of other organisms for their nutrition". This is known as heterotrophy .
- Plants do not get their food from other organisms, so their building metabolism is called autotrophy .
It was later recognized why this is so: Plants are autotrophic because they meet their carbon needs for growth from carbon dioxide, which is also found in the air . They operate carbon assimilation through CO 2 fixation and reduction . Autotrophy is an ability that heterotrophic organisms lack.
energy
Plants need light for their growth, so nothing "material". The question has therefore long been what role light plays in (plant-based) nutrition. Nevertheless, the name was used
- Phototrophy , "nutrition" by light.
At this level of knowledge, the terms autotrophy and phototrophy could still be used synonymously, and some biology textbooks still do that today. In fact, however, heterotrophy denotes the carbon source, while phototrophy denotes the energy source. When it became clear that phototrophy is about energy that is obtained from light in phototrophic organisms, another term was coined:
- Chemotrophy . Chemotrophic organisms cannot use light as an energy source; they only gain their energy from the chemical conversion of substances that they absorb from their environment. Phototrophy is an ability that chemotrophic organisms lack.
The apparently sensible division of living things into phototrophic and heterotrophic organisms was shaken by the microbiologist and plant physiologist Sergei Nikolajewitsch Winogradski (1856-1951). He discovered bacteria that grow in the dark in media that contain only inorganic compounds. These strange creatures are neither phototrophic nor heterotrophic. They do not tolerate light, but are clearly autotrophic and not heterotrophic and they assimilate CO 2 as the only carbon source. Many of these organisms cannot grow on nutrient media with organic substances because they inhibit their growth. They need very specific inorganic substances, from whose chemical conversion they can generate energy. Examples: ammonia plus oxygen (among others Nitrosomonas ), hydrogen plus sulfate (among others Desulfovibrio ).
- The energy metabolism of these organisms that feed on "lithotrophic" (literally translated: "eating stones") is what Winogradsy called "inorganic oxidation". In the meantime, the "nourishment" of the organisms that gain their energy from a chemical reaction and at the same time build their body material through the assimilation of CO 2 is called chemo-autotrophy .
At this time the term lithotrophy was coined . But at that time it was not yet clear that these organisms use the inorganic "nutrients" not only for energy production. The inorganic reducing agents they use for another metabolic path, the fundamental importance of which was only recognized later.
Electron donor
Autotrophic creatures not only need an energy source and a carbon source, because the assimilation of CO 2 as a carbon source also requires a reducing agent, namely NADPH, in order to convert the CO 2 into cell material. NADPH is consumed (oxidation to NADP + ) and autotrophic organisms need not only energy but also an electron donor for its regeneration . Plants use water for this, which is oxidized to O 2 . In prokaryotes there are also photosynthetic organisms that do not use water but other inorganic substances as electron donors, for example hydrogen sulfide or nitrite, or some organic substances.
Winogradsky's organisms that assimilate CO 2 in the dark use the electron donor to regenerate NADPH, which they also use for the redox reaction from which they gain energy.
According to the electron donor used for NADP regeneration, one subdivides into
- Lithotrophy : a metabolism in which inorganic substances are used as electron donors for NADPH regeneration. For this, lithotrophic organisms mostly need energy (except in the case of H 2 ).
- Organotrophy : a metabolism in which organic matter is used for NADP regeneration. Organotrophs are not able to use inorganic electron donors, so they lack the ability to lithotrophy.
Conceptual clarifications
- Lithotrophy does not mean that such organisms get their energy from the reaction of inorganic compounds. Plants are also lithotrophic.
- Organotrophic organisms do not differ in which organic compounds they use to generate energy, but in how they regenerate NADPH. There are phototrophic bacteria that use organic electron donors for NADPH regeneration.
- Phototrophy does not mean that such organisms are autotrophic. There are organisms that use light to generate energy, but cannot assimilate CO 2 .
- Chemotrophic organisms differ in which chemical compounds they use to generate energy. Whether they are lithotrophic or autotrophic has nothing to do with their energy production .
Individual evidence
- ↑ General Microbiology 2014
- ↑ G. Gottschalk: Bacterial Metabolism. 2nd Edition. Springer, New York 1986, p. 288.
- ↑ Shuning Wang, Haiyan Huang, Jörg Kahnt, Rudolf K. Thauer: A Reversible Electron-Bifurcating Ferredoxin- and NAD-Dependent [FeFe] -Hydrogenase (HydABC) in Moorella . In: Journal of Bacteriology . 195, No. 6, 2013, pp. 1267-1275. doi : 10.1128 / JB.02158-12 .
- ↑ Dadachova E, Bryan RA, Huang X, Moadel T, Schweitzer AD, Aisen P, Nosanchuk JD, Casadevall A: Ionizing Radiation Changes the Electronic Properties of Melanin and Enhances the Growth of Melanized Fungi . In: PLoS ONE 2 (2007): e457 doi : 10.1371 / journal.pone.0000457 pdf