Chemotactic heterotrophic microorganisms use organic matter as carbon source and chemical energy generated by oxidation of organic matter as energy source. Therefore, organic compounds are both the carbon source and the energy source of these bacteria. Most known microorganisms belong to this category. Chemotactic heterotrophic microorganisms can be divided into parasitic and saprophytic types. Parasitism refers to the phenomenon that one organism lives in or on the surface of another organism, thus absorbing the nutrition of the host cell to maintain life. Saprophytic organisms refer to a way of life to maintain their normal life by decomposing dead organisms or other organic substances.

According to the different electron acceptors in redox reaction, heterotrophic microorganisms can be divided into fermentation and respiration, and respiration can be divided into aerobic respiration and anaerobic respiration. I. Four main ways of dehydrogenation of substrate (matrix)

Taking glucose as a typical substrate

1, EMP route (glycolytic pathway)

When it is aerobic, it is connected with TCA and completely oxidizes pyruvate into carbon dioxide and water.

During hypoxia, pyruvate is further metabolized into related products.

2.HMP pathway (hexose-phosphate pathway)

Produce a large number of NADPH2 and a variety of important intermediate metabolites.

3.ED pathway 2- keto -3- deoxy -6- phosphogluconic acid cleavage pathway KDPG

For some microorganisms lacking complete EMP, this is an alternative way, and bacterial alcohol fermentation is carried out through ed.

4.TCA cycle (tricarboxylic acid cycle)

Eukaryotes are in mitochondria and prokaryotes are in cytoplasm.

TCA plays an important pivotal role in metabolism.

Second, hydrogen transfer and hydrogen acceptance

Accord to different classifications of hydrogen transport, especially that final hydrogen acceptor

1, fermentation (intramolecular respiration)

Under anaerobic conditions, the reducing force produced by substrate dehydrogenation is directly transferred to an intermediate metabolite, and there is no respiratory chain, which is an inefficient productivity reaction.

In this process, organic matter is the oxidation matrix, the ultimate hydrogen acceptor and the product of incomplete oxidation. Therefore, organic matter is still accumulating and productivity is very low.

In the fermentation process, the only way to synthesize ATP is the phosphorylation of substrate. High-energy compounds: 1, 3- diphosphoglyceric acid, acetyl phosphate, carbamoyl phosphate, PEP, acyl coenzyme A.

2. Aerobic breathing (breathing)

After the substrate is dehydrogenated, hydrogen is transported through a complete respiratory chain (electron transfer chain), and molecular oxygen, as the final hydrogen acceptor, generates water and releases energy.

In the process of electron transfer, ATP is produced by coupling with oxidative phosphorylation, which is called oxidative phosphorylation.

1) Composition and sequence of respiratory chain:

2) Comparison of respiratory chains between eukaryotes and prokaryotes:

Position, composition

3. Anaerobic Breathing (Anaerobic Breathing)

Biooxidation with inorganic oxides as the ultimate hydrogen acceptor instead of molecular oxygen.

Oxidative phosphorylation synthesizes ATP, but part of the energy is transferred to the final receptor, and the productivity is not much.

According to the final hydrogen acceptor, it can be divided into many types.

1) nitrate reduction (denitrification)

The process of gradually reducing nitrate to molecular nitrogen. Soil nitrogen loss and fertility reduction. It belongs to alienated nitrate reduction.

2) Sulfate Reduction (Alienation)

Lactic acid is usually used as the substrate for accumulating acetic acid, and SO42- is the ultimate hydrogen acceptor. Vibrio desulfurization.

3) Biogas fermentation

Methanogenic bacteria take carbon dioxide as the ultimate hydrogen acceptor. Such as methanobacteria.