Types and products of bacterial metabolism

Metabolism we understand the transformation of substances and energies, it consists of anabolism and catabolism. Anabolism is a set of reactions by which the organism synthesizes more complex substances from simpler substances, energy is consumed (endergonic reactions). Catabolism is a set of reactions in which simpler substances arise from more complex substances and energy is released in the form of chemical, mechanical, electrical, osmotic, light or thermal work (exergonic reactions).

In a healthy adult organism, these events are in balance. The general energy carriers between catabolism and anabolism are macroergic compounds, the most important is ATP (adenosine-5´-triphosphate), other chemical energy transporters include 1,3-bisphosphoglycerate, creatine phosphate, phosphoenolpyruvate and others.

Types of metabolism
All microorganisms can be divided into:
 * depending on what energy they use on
 * phototrophic (use light energy);
 * chemotrophic (use the energy of chemical bonds);
 * according to the source of reduction equivalents at
 * lithotrophic (reducing equivalents derived from inorganic compounds);
 * organotrophic (reducing equivalents derived from organic compounds);
 * by carbon source to
 * heterotrophic (carbon derived from organic compounds);
 * autotrophic (carbon derived from carbon dioxide);
 * mixotrophic (they acquire carbon heterotrophically and autotrophically).

Photolithoutautotrophic bacteria
They obtain energy from light, reducing equivalents from inorganic compounds, the carbon source is CO2. Among these bacteria are Cyanobacteria, which guarantee oxygen photosynthesis, H2O is a donor of reducing equivalents, resulting in O2 as a by-product and a major product glucose. This also includes the bacteria responsible for anoxygenic photosynthesis – Chlorobiaceae, Chromatiaceae (H2S is a donor of reducing equivalents), Chloroflexus (H2 is a donor of reducing equivalents).

Photo Organ Heterotrophic bacteria
They obtain energy from light, reducing equivalents and carbon from organic compounds. Some species may use CO2, they are mixotrophic. As an example I will mention: Rhodobacter, Rhodopseudomonas, Rhodospirillum, Rhodomicrobium, Rhodocyclus, Heliobacterium.

Chemolithoutotrophic bacteria
They obtain energy and reducing equivalents by oxidizing inorganic compounds and carbon from CO2. This group includes, for example:sulfur (Beggiatoa), nitrifying (nitrosomonas, nitrobacter, which have an irreplaceable role in the N2 cycle), iron bacteria (Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans).

Chemoheterotrophic bacteria
They obtain energy and reducing equivalents by oxidizing inorganic compounds and carbon from organic compounds. Examples: some bacteria of the genus Thiobacillus, Beggiatoa, Nitrobacter.

Chemoorganoheterotrophic bacteria
They extract energy, carbon and reducing equivalents from organic compounds. These bacteria are medically most important. This probably includes all bacteria in medical microbiology textbooks. Chemoorganotrophic bacteria are further classified according to their ability aerobic respiration, anaerobic respiration or fermentation.

Fermentation
preview Right cultivation of Salmonella enterica enteritidis on deoxycholate-citrate agar Fermentation is a process that releases energy from sugars, organic acids, purines or pyrimidines, does not require oxygen, does not use an electron-transport system, produces a small amount of ATP, oxidizes reducing equivalents (necessary for glycolysis) and releases gases (CO2).It is used in industry and in biochemical identification of bacteria. Simplified fermentation model: glucose is converted to pyruvate,he is converted to lactate (some Streptococcus spp., Lactobacillus spp.) or on ethanol and CO2 (yeast) or propionate (Propionibacterium spp). There are usually more end products - ethanol, lactate, succinate, acetate, CO2 and H2 (Salmonella spp., Escherichia spp.).

Aerobic respiration
Set of events - glycolysis, Krebs cycle, respiratory chain, (electron transport system) – leading to electron transport to oxygen, it arises proton gradient. Protons tend to pass through the pump, ATP synthase ,which synthesizes ATP until the gradient resets. Aerobic respiration takes place in prokaryotes on cytoplasmic membranen in eukaryotes in the cytosol mitochondria and on the inner mitochondrial membrane (one of the proofs of the theory ofendosymbiosis).

Anaerobic respiration
preview 150px Pseudomonas aeruginosa - Gram's stainn It uses elektron-transport system, at the end of which the final electron acceptor is not oxygen but another substance. This other substance may be nitrate NO3- (reduced to nitrite NO2- or to gaseous N2 - Paracoccus denitrificans and pseudomonads) or sulphate SO42- (reduced to hydrogen sulphide HS-, Desulfovibrio spp.), CO2 (reduced to methane CH4, Methanothrix thermophila) or fumarate (reduced to succinate, Bacteroides spp.). Other acceptors can be ions selenium, iron, arsenic etc. This type of respiration generates less ATP than aerobic respiration because only part of the Krebs cycle is used.

Lipid and protein catabolism
For completeness, it should be mentioned that bacteria have lipases, which it cleaves fats on fatty acids and glycerol. Glycerol enters as glyceraldehyde-3-phosphate into glycolysis and is subject to fatty acids beta-oxidation, in which it splits acetylcoenzym A,which enters the Krebs cycle. Glycerol and fatty acids can enter the fat anabolism. Proteases and peptidases serve to catabolize protein. They arise from them aminoacids, which undergo mainly deamination or transamination, whose carbon skeletons enter the Krebs cycle or anabolic reactions.

Anabolism
ATP obtained by catabolic processes is consumed during movement, drive membrane pumps and especially during anabolism. Bacteria synthesizepolysacharid, peptidoglykan, lipids (e.g. phospholipid, cholesterol), amino acids, proteins, purines, pyrimidines, RNA and DNA and more.

Bacterial-bacterial, bacterial-host metabolism interactions
It should be noted that there is no interaction between catabolism and anabolism neither in the bacterial cell nor between the bacteria nor between the bacteria and the host. Bacteria live in a kind of dynamic equilibrium, compete for substrates (increase the expression of an enzyme that utilizes a given substrate), or cooperate. This balance, for example in the intestine, can be disturbed antibiotic or a food ingredient that favors certain bacteria.
 * Example of a bacterium-bacteria interaction: primary fermenters produce H2 as a by-product, which suppresses NAD + regeneration from NADH + H +. Without NAD +, glycolysis would not occur. The H2 level is maintained thanks to bacteria that use H2 - eg methanogenic, ethanogenic.
 * Example of bacterial-bacterial-host metabolism interaction: Clostridia in amino acid processing produce NH3, which is utilized by Bacteroides spp. - hydrolyze oligosaccharide ends glykoprotein thereby releasing more peptid for Clostridia. Both Bacteroides and Clostridia synthesize the short chains of fatty acids they receive enterocyte for a host that provides CO2 for Bacteroides during its metabolism.

related articles

 * Bacteria
 * Metabolism