Diversity of Metabolism in Procaryotes

Eli Komalawati 10406028

Bakteriologi BM-3204

Introduction

The unicellular eucaryotes (protista) exhibit a fair amount of structural diversity, but the procaryotes (bacteria and archaea) lack this distinction.

There are a few basic morphologies, the possibilities of motility and resting cells (spores), and a major differential stain (the Gram stain) that differentiates procaryotes microscopically.

Biochemical or metabolic diversity, especially as it relates to energy-generating metabolism and biosynthesis of secondary metabolites.

The diversity of procaryotes is expressed by their great variation in modes of energy generation and metabolism, and this feature allows procaryotes to flourish in all habitats suitable for life on earth.

Energy-Generating Metabolism Metabolism :- catabolism : energy-generating- anabolism : energy-consuming

Catabolic reactions produce

energy as ATP, which can be

utilized in anabolic reactions

to build cell material from

nutrients in the environment.

Figure 1. The relationship between catabolism and anabolism

ATPATP - adenosine triphosphate : the universal currency of energy exchange in biological systems.

Figure 2. The structure of ATP

NAD NAD (Nicotinamide Adenine Dinucleotide) : coenzyme commonly involved in energy-producing metabolism

Figure 3. The Structure of NAD

Coenzyme A

Coenzyme A is involved in a type of ATP-generating reaction seen in some fermentative bacteria and in all respiratory organisms.

Figure 4. (a) The Structure of Coenzyme A. CoA-SH is a derivative of ADP. The molecule shown here attached to ADP is pantothenic acid, which carries a terminal thiol (-S) group. (b) the oxidation of the keto acid, pyruvic acid, to acetyl~SCoA.

ATP Synthesis in Procaryotes

Cells fundamentally can produce ATP in two ways : 1.substrate level phosphorylation : ATP is made

during the conversion of an organic molecule from one form to another

2.electron transport phosphorylation : drive electrons through an electron transport system (ETS) in the membrane, establish a proton motive force (pmf), and use the pmf to synthesize ATP

Substrate Level Phosphorylation

Figure 5. Three examples of substrate level phosphorylation. (a) and (b) are the two substrate level phosphorylations that occur during the Embden Meyerhof pathway, but they occur in all other fermentation pathways which have an Embden-Meyerhof component. (c) is a substrate level phosphorylation found in Clostridium and Bifidobacterium. These are two anaerobic (fermentative) bacteria who learned how to make one more ATP from glycolysis beyond the formation of pyruvate.

Electron Transport Phosphorylation

Figure 6. The plasma membrane of Escherichia coli.

Heterotrophic Types of Metabolism

Heterotrophy is the use of an organic compound as a source of carbon and energy.

Heterotrophic bacteria are the masters of decomposition and biodegradation in the environment.

Heterotrophic metabolism is driven mainly by two metabolic processes : fermentations and respirations.

1. Fermentation : metabolism in which energy is derived from the partial oxidation of an organic compound using organic intermediates as electron donors and electron acceptors. All ATP is produced by substrate level phosphorylation.

Figure 7. Model fermentation

In procaryotes there exist three major pathways of glycolysis (the dissimilation of sugars):

- Embden-Meyerhof pathway, which is also used by most eucaryotes, including yeast (Saccharomyces);

- Phosphoketolase or heterolactic pathway related to the hexose-pentose shunt;

- Entner-Doudoroff pathway

The Embden-Meyerhof Pathway

Figure 8. The Embden Meyerhof pathway for glucose dissimilation.

Figure 9. (a) The Embden Meyerhof pathway of lactic acid fermentation in lactic acid bacteria (Lactobacillus) and (b) the Embden Meyerhof pathway of alcohol fermentation in yeast (Saccharomyces).

Bacterial fermentations are distinguished by their end products into the following groups :No. Groups End Product Bacteria

1. Homolactic Fermentation

Lactic acid homolactic acid bacteria (Lactobacillus, Lactococcus and most streptococci)

2. Mixed Acid Fermentations

A mixture of lactic acid, acetic acid, formic acid, succinate and ethanol, gases (CO2 and H2)

Enterobacteriaceae

2a. Butanediol Fermentation

Mixed acids and gases, 2,3 butanediol, acetoin

Enterobacteriaceae

3. Butyric acid fermentations

Butyric acid, acetic acid, CO2 and H2

clostridia

3a. Butanol-acetone fermentation

Butanol and acetone Clostridium acetobutylicum

4. Propionic acid fermentation

Propionate, acetic acid, CO2 and propionic acid

propionic acid bacteria which include corynebacteria, Propionibacterium and Bifidobacterium

The Heterolactic (Phosphoketolase) Pathway

Figure 10. The heterolactic (phosphoketolase) pathway of fermentation. The overall reaction in the fermentation of glucose is Glucose -------> Lactic acid + ethanol + CO2 + 1 ATP (net).

The Entner-Doudoroff Pathway

Figure 11. The Entner-Doudoroff Pathway of Fermentation. The overall reaction is Glucose -------> 2 ethanol + 2 CO2 + 1 ATP (net).

2. Respiration : result in the complete oxidation of the substrate by an outside electron acceptor.

Besides pathway of glycolysis, four essential metabolic components are needed :

1. The tricarboxylic acid (TCA) cycle (Kreb's cycle): used for the complete oxidation of the substrate. The end product is CO2.

2. A membrane and an associated electron transport system (ETS).

3. An outside electron acceptor. For aerobic respiration the electron acceptor is O2. But in anaerobic respiration, the final electron acceptors may be SO4 or S or NO3 or NO2 or fumarate.

4. A transmembranous ATPase enzyme (ATP synthetase). This enzyme utilizes the proton motive force established on the membrane to synthesize ATP in the process of electron transport phosphorylation.

Figure 12. Model of aerobic respiration.  

Lithotrophic Types of Metabolism Lithotrophy is the use of an inorganic compound

as a source of energy.

physiological group energy source oxidized end product

organism

hydrogen bacteria H2 H2O Alcaligenes, Pseudomonas

methanogens H2 H2O Methanobacterium

carboxydobacteria CO CO2 Rhodospirillum, Azotobacter

nitrifying bacteria* NH3 NO2 Nitrosomonas

nitrifying bacteria* NO2 NO3 Nitrobacter

sulfur oxidizers H2S or S SO4 Thiobacillus, Sulfolobus

iron bacteria Fe ++ Fe+++ Gallionella, Thiobacillus

* The overall process of nitrification, conversion of NH3 to NO3, requires a consortium of microorganisms.

Table 2. Physiological groups of lithotrophs

Phototrophic Metabolism Phototrophy is the use of light as a source of

energy for growth, more specifically the conversion of light energy into chemical energy in the form of ATP.

Procaryotes that can convert light energy into chemical energy include the photosynthetic cyanobacteria, the purple and green bacteria and the "halobacteria" (actually archaea).

Autotrophic CO2 fixation Use CO2 as a source of carbon for growth by using

RUBP carboxylase and the Calvin cycle for CO2 fixation.

Figure 22. The Calvin cycle and its relationship to the synthesis of cell materials.

Biosynthesis

Figure 25. The main pathways of biosynthesis in procaryotic cells

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