Autotrophic metabolism energy producer

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* Nitrifying Bacteria

* Methylotrophic

* Phototrophs

* Components of the photosynthetic apparatus

* Rates of photosynthesis

They get their energy from light (phototrophs), oxidation of inorganic compounds (chemolithoautotrophic) or oxidation of methyl groups attached to different carbon atoms (methylotrophic).


In chemolithotrophs, the electron donor is an inorganic molecule reduced. This ability to gain energy by oxidative phosphorylation from inorganic electron donors has only evolved in some groups of prokaryotes. The chemolithotrophs can be classified into groups according to type of physiological inorganic donor “breathe”

The chemolithotrophs “typical” respirators are generally aerobic, ie, the final electron acceptor is molecular oxygen. There are several types depending on the type of inorganic electron donor oxidized:

* Hydrogen-oxidizing bacteria (oxidize H2 to H2O)

* Ferrroso iron oxidizing bacteria (pass Fe2 + to ferric, Fe3 +)

* Reduced sulfur oxidizing bacteria: sulfide (S2-) and elemental sulfur (S0). The total oxidation of the reduced sulfur leads to the production of sulfuric acid (SO4H2)

* Nitrifying bacteria, with two different subtypes:

* The ammonia-oxidizing (nitrous calls, breathing convert NH3 to NO2-)

* The nitrite-oxidizing (called Nitric breathing convert NO2-to NO3-)

Recently discovered a new type of chemolithotrophs, which docked in anaerobic oxidation of ammonia to nitrite reduction, and water to produce molecular nitrogen (NH4 + + NO2-to N2 + 2 H2O). This process has been termed the anaerobic ammonia oxidation (anammox in the acronym, which easily can be translated as Oxanamide in Spanish abbreviation, unfortunately little used).

Anammox bacteria (as Brocadia anammoxidans) are members of the phylum of Planctomicetos, a fascinating group of walled eubacteria protein (without peptidoglycan), and cytoplasm compartmentalized through special membranes. Gender Brocadia has an organelle surrounded by this special type of membrane, called anamoxisoma where this reaction occurs anammox. The discovery of this process has involved a review of our traditional ideas about the nitrogen cycle in nature (it was thought that the ammonia was stable under anaerobic conditions), and may have practical consequences in the field of environmental protection as it industrial processes have been designed to eliminate anoxic ammonia and amines from waste water.

The mechanism of ATP generation in chemolithotrophs chemoorganotrophic is similar to respirators: the electrons extracted from exogenous donor (in this case inorganic) pass an electron transport chain to a final acceptor (usually oxygen in typical CHEMOLITHOTROPHY and which is nitrite in the anammox), generating a proton-motive force that turns into ATP by ATP synthase.

But with the exception of H2, the other inorganic electron donors have a reduction potential E0 ‘lower than that of NADH, so that the inorganic oxidation of these donors can only generate energy but not directly reducing power. Reducing power used for reverse transport of electrons: Part of the electrochemical gradient created during respiration is used to make electrons travel through the electron transport chain (or part thereof) in reverse order to reduce NAD +.


The H2 is a product of microbial metabolism. Is a taxonomic group varied, is divided into:

1.A aerobic bacteria oxidizing hydrogen: hydrogen bacteria, the final acceptor is O2. Are typical chemolithoautotrophic. Used as flux to the Calvin cycle

2H2 + O2 2H2O a

1.B Anaerobic bacteria: the final acceptor is another different compound to oxygen.Overall:

* The hydrogen bacteria are: Pseudomonas, Paracoccus, Alcaligenes, etc.

* Many are chemolithoautotrophic optional. Can also grow using organic compounds as chemoorganotroph.

* All bacteria have a key enzyme that is membrane-bound Hydrogenase, cleaves the H2 and gave a chain e-transport of electrons. Establishing the gradient of H + to form ATP. Are associated with the plasma membrane and components of the electron transport chain.

Some microorganisms possess soluble hydrogenase transfers electrons directly obtained coenzymes and reducing power, eg, Alcaligenes eutrophus. NADH or NADPH can occur by other enzymes which are the transhydrogenase:


No need to reverse the flow of e-. Give better cell yields and rapid growth. Do not spend to create the NADH ATP.

When grown autotrophic use the Calvin cycle:

There are bacteria that can grow mixotrophic: use the H2 as a source of e-and use an organic compound as carbon source.

Nitrifying bacteria

Nitrifying bacteria (BN) or perform the oxidation of ammonia to nitrite (NH3 to NO2-) as G. Nitrosomonas; or oxidation of nitrite to nitrate (NO2-to NO3-) as G. Nitrobacter.

Ammonia-oxidizing bacteria and nitrite.


Nitrification: The process widely distributed in nature and involves the sequential action of these two types of bacteria.

In the case of bacteria that use the oxidation of NH3 to NO2-:

* It is produced by an intermediate step in the NH3 passes hydroxylamine (nH2O), the enzyme involved is a monooxygenase which produces the oxidation of NH3. In the second step the nH2O is oxidized to NO2-by-hydroxylamine oxidoreductase.

* The first is a constitutive enzyme linked to the cell membrane, the second acts at the periplasm.

* E-needed to reduce the NH3 derived from the direct transfer of hydroxylamine-oxidoreductase to cytochrome c for the e-transport chain to oxygen generating a proton motive force to generate ATP.

In bacteria that perform the oxidation of NO2-to NO3-:

Is performed by an enzyme nitrooxidasa, in this case the e-cytochromes are incorporated on the chain is very short and the performance of ATP generation is not very high. Chemolithoautotrophic metabolism is typically live in aerobiosis. Sometimes the NH3 may be oxidized to nitrate anoxia per share, e-acceptor for the formation of H2. Highly exothermic reaction with high energy release.

BN is used in the Calvin cycle to fix CO2, because some organic compounds used in CO2 fixation is energy intensive.

Bacteria responsible for nitrification

THE methanogenic archaea are the only living beings capable of obtaining energy by coupling the oxidation of molecular hydrogen with the use of CO2 as an electron acceptor (acting in such conditions as chemolithotrophs)

CO2 + 4H2 CH4 + 2H2O

In addition, some methanogens are not only CHEMOLITHOTROPHY, but also set the carbon autotrophic, although special routes other than the Calvin cycle.

Ferric iron (FE3 +) can be used in nature as an electron acceptor by certain bacteria chemoorganotroph (Shewanella putrefaciens) and chemolithotrophs (Geobacter metallireducens is CHEMOLITHOTROPHY Optional: You can use as electron donor molecular hydrogen and simple organic compounds).


Methylotrophic when a microorganism is used as carbon and energy source of methane, methanol and other compounds reduced carbon atom under aerobic conditions. This means that the organism can produce their own organic compounds using carbon sources such as small molecules, and can oxidise for metabolic energy.


The phototrophy is the ability to capture light energy. Although the ability to use light as a source to generate ATP (photophosphorylation) depends on a mechanism characteristic in common with oxidative phosphorylation that also produces an electrochemical gradient of protons on either side of a membrane, which in ATP-synthase turn feeds. Strictly speaking, refers to the fotoautotrofia photosynthesis, ie the combination of phototrophy or capture of the light energy (obtained in the “stage light”) to use to fix CO2 (autotrophy) to cellular material (“dark phase” .) Leaving aside the type of electron donor, the general equation for photosynthesis is:

light energy (hn)

H2A + CO2 2 ———————————————- ——> [CH2O] + H2O + 2 A

* In cyanobacteria, algae and green plants, H2A = H2O, as a reducing agent. Therefore, the oxidation is generated O2 (oxygenic photosynthesis)

* In anoxygenic photosynthetic bacteria can be H2A H2, H2S, S2O3-etc. Obviously, they can release oxygen (anoxygenic photosynthesis).

* On the other hand, there are phototrophic prokaryotes that capture light energy, but use organic matter as carbon source, so called photoheterotrophic.

More than half of our planet’s photosynthesis is due to photosynthetic bacteria.

For photosynthesis is necessary certain photosynthetic pigments are mainly chlorophylls, which absorb quanta, and are tetrapyrrole ring with an atom of Mg2 + in the center. In a ring is a long chain of phytol, which inserts into a membrane molecule of chlorophyll. Can carry different substituents on the ring and get different chlorophylls, Chl a and Chl b absorb between 680-700nm, also absorb at 340, ie there are two peaks in the absorption spectrum of chlorophyll, the peak of 300 nm is in the red while 700 nm in the blue. Emitted in the intermediate region, the green.

There bacteriochlorophylls ranging from a to f, absorbed 870 nm to 1020 nm occupy regions of the spectrum that do not occupy the chlorophylls. A plant and bacteria do not compete for the same wavelength, light occupy different niche so that they can live.

When a chlorophyll lacking Mg2 + are pheophytin.

The growth of a photoautotrophs is characterized by two types of reactions:

Phase .- Light: da ATP and reduced coenzymes with reducing power (e-for the reduction of CO2). With light.

.- Dark phase: the ATP and NADPH formed above processes are used to reduce and fix CO2. No light.

NADPH can be caused by the oxidized form by e-from different external donors.


Photosystems: catalyze the conversion of light energy, captured in excited molecules of chlorophyll or bacteriochlorophyll in a useful form of energy. They consist of complex antenna (light-harvesting pigments) and reaction center (with photoactive chlorophylls or bacteriochlorophylls). Reaction centers are usually located within membranous structures:, chromatophores (membrane invaginations) of anoxygenic purple bacteria or cytoplasmic membrane itself (green anoxygenic bacteria heliobacteria).

Electron transport chain, these chains are located in membranes closely linked to the reaction center, creating a proton-motive force.

A) Chlorophylls and bacteriochlorophylls. These cyclic tetrapyrroles chelated Mg2 +, and having long chain alcohol (phytol) may form part of both the antenna pigments and reaction centers.

* Chlorophylls not participating in the reaction center function as part of the antenna system, and can reach about 300 in each of these systems.

* The reaction center chlorophylls are much less abundant than the antenna complex. Typically there are 4 molecules, of which two are associated with proteins, so that in this state act as “traps” for light quanta. As we shall see, these special chlorophyll after arousal, are oxidized, so called photoactive chlorophylls. The light makes these chlorophylls from ground state to its excited state, which has an E0 ‘negative, so that then can transfer electrons (oxidize) easily.

B) Carotenoids. Are part of the antenna complex. Its functions are:

* Protection against potentially harmful effects resulting from interactions between light and oxygen;

* As antenna pigments, light-harvesting (though less efficient than others).

C) In cyanobacteria, there is also a set of phycobiliproteins, organized in supramolecular complexes called phycobilisomes, arranged on the surface of thylakoids. Major phycobiliproteins are phycocyanin, phycoerythrin and allophycocyanin, and form the antenna complex in cyanobacteria.

D) pheophytin and bacteriopheophytin. Are similar to the respective (bacterio) chlorophyll s, except that there are chelated with Mg + +. Act as electron acceptors immediate lost each (bacterio) chlorophyll reaction center.

E) Other components. In the same reaction center are the first components of the cte photosynthetic: Special quinones complexed with Fe Moreover, the cte photosynthetic types contain molecules similar to those already studied in cte Respiratory quinones, cytochromes and nonheme ferroproteinas.


Oxygenic photosynthesis: the generation of ATP and reducing power takes place in two different photochemical reaction called photosystem I (PSI) and photosystem II (PSII), which contain chlorophyll and are located in the thylakoid membranes. The two photosystems operate in a joint in cyanobacteria, algae and plants. i) When light is absorbed by chlorophyll molecules present in the PSI, these light-activated chlorophyll molecules allowing them to rust. The electrons removed from the PSI chlorophyll molecules are accepted by the reduced NADP to NADPH 2.

All this leaves the PSI chlorophyll molecules temporarily deficient in electrons, which gives them a positive charge. ii) Similarly, the light absorbed by chlorophyll molecules present in the PSII causes an electron is removed from each molecule. These electrons pass through an electron transport system until they reach the PSI which are accepted by the chlorophyll molecules deficient in electrons is reduced. This electron transport system is similar to that described in oxidative phosphorylation, using the energy released for the synthesis of ATP.

The difference is that the primary electron donor is the chlorophyll in PSII and the terminal electron acceptor is the chlorophyll of PSI (NADH2 and O2, respectively, in oxidative phosphorylation). iii) At this point the chlorophyll of PSII is deficient in electrons. However, this chlorophyll is a strong oxidizing agent to get the electrons needed to reduce the molecules of H2O. This oxidation generates oxygen gas H2O. Cyanobacteria, algae and plants are organisms that produce oxygen by oxygenic photosynthesis, being responsible for the majority of the production oxygen in the atmosphere. The early Earth’s atmosphere contained no oxygen until it cyanobacteria developed between 1000 and 3000 million years.

The development of aerobic organisms was only possible after they accumulated in the atmosphere significant amounts of O2 (generated by oxygenic photosynthesis of cyanobacteria).

Anoxygenic photosynthesis: The anoxygenic phototrophs convert light energy into chemical energy necessary for growth, however, and unlike plants, algae and cyanobacteria in this process of transformation of energy does not produce oxygen and therefore it called anoxygenic photosynthesis. Another difference is that anoxygenic phototrophs contain a type of clrofila, bacteriochlorophyll, chlorophyll than plants. These bacteria also contain carotenoid pigments responsible for the absorption of light energy and subsequent transfer to bacteriochlorophyll.

The color of these pigments are what give the name of these bacteria: bacteria, red and green bacteria. In cyanobacteria these light-harvesting pigments are phycobilins, hence its name: blue bacteria (cyanobacteria).

In bacteria, red and green bacteria there is only one photosystem, so that the energy absorbed from light is used to transport an electron from chlorophyll to the electron transport chain that finally gives the electron to the same chlorophyll. In this electron transport chain generates the energy needed to synthesize ATP. However, electron transport is cyclic (the primary electron donor and terminal electron acceptor is the same chlorophyll) and therefore there was no reduction of NADP to NADPH.

This reduction was accomplished by reverse transport of electrons by electrons donated by the hydrogen gas (H2) or hydrogen sulfide (H2S). In any event never occurs O2.


Juan Francisco Zuniga Huayamis