Physiology of bacteria

2021-08-27 05:20 PM

Most bacteria, if provided with all of these factors, are able to synthesize the structural substances of the cell. But some bacteria lose the ability to synthesize some compounds

Physiology of bacteria

Like other organisms, bacteria also feed, flower, and grow.


The growth of bacteria requires a culture medium that contains a complete set of nutrients, including those necessary for energy and those that are used as raw materials for the synthesis of new cellular materials. Regarding synthetic materials, bacteria require mineral salts such as PO43-, K+, Mg2+ in significant amounts, some ions (trace elements) only need at a very low concentration such as Fe2+, Zn2+, Mo2+, Ca2+, these ions are often found in water and in impure mineral salts. The source of C is provided by food for energy. The N source is usually a protein or an ammonium salt.

Most bacteria, if provided with all of these factors, are able to synthesize the structural substances of the cell. But some bacteria lose the ability to synthesize some compounds and require them to be supplied in culture. Those are development factors; they are divided into two types, one that needs to be supplied in small amounts and serves as a catalyst as part of an enzyme such as vitamin B, the other that needs to be supplied in large amounts and used as a raw material cellular structure such as amino acids, purines, and pyrimidines.

In addition, the physical conditions such as pH temperature, oxygen pressure, which affect the growth of the balance, are adjusted appropriately.

The transferability

Includes all chemical reactions that occur in living cells. Through these reactions, energy is extracted from the environment and used for biosynthesis and growth. In metabolism, the most important is biological oxidation.

Biological oxidation

Oxidation is defined as the removal of electrons from a substrate accompanied by the removal of a hydrogen ion i.e. the removal of a hydrogen atom. Therefore, oxidation is referred to as the transport of hydrogen atoms. The oxidized substrate is called the hydrogen donor and the reduced product is called the hydrogen acceptor. Most organic compounds lose hydrogen ions by electron removal. An electron cannot be in a free state in solution and cannot be removed from a substrate without a suitable acceptor. Electron transport is at the core of oxidation and reduction.

Depending on the nature of the final hydrogen acceptor, biological oxidation is divided into three forms: aerobic respiration, anaerobic respiration, and fermentation. The final hydrogen acceptor is molecular oxygen (O2) in aerobic respiration, an inorganic compound (nitrate, sulfate, carbonate) in anaerobic respiration, an organic compound in fermentation.

Regarding oxygen demand, people are divided into:

Obligate aerobic bacteria such as tuberculosis and some spore-forming bacilli are oxygen hungry because of their lack of fermentation capacity.

Obligatory anaerobes like Clostridia, Propionibacterium, only grow in the absence of oxygen.

Arbitrary bacteria such as yeast, intestinal bacteria. These bacteria can live without oxygen but convert to respiratory metabolism in the presence of oxygen.

Aerobic respiration

The final hydrogen acceptor is molecular oxygen. Common substrates are sugars but can also be fatty acids, amino acids. Electrons are transferred from the hydrogen donor to the hydrogen acceptor in several steps. Electrons taken from the hydrogen donor can first transfer to a first coenzyme A, A, thereby being reduced to AH2. Another enzyme catalyzes the electron transfer from AH2 to a second coenzyme B. AH2 is thus oxidized back to A and B becomes BH. This process can continue through many steps that make up the electronic respiratory chain from hydrogen donor to oxygen

Illustration of an electronic chain

Image. Illustration of an electronic chain

The end result is the formation of an oxidation product, a reduction product, and energy. Energy is generated or stored in pre-energized wires or radiated as heat.

Anaerobic respiration

The substrate can be an organic compound, but it can also be an inorganic substance. The electron acceptor here is not air oxygen but nitrate, sulfate, carbonate...


The substrate is an organic compound, but the electron nucleus is also an organic compound. Here, in a conventional electron chain, only NAD is the intermediate electron carrier. 

Electron transfer in fermentation

Image. Electron transfer in fermentation

Compared with respiration, fermentation is much less efficient, providing 19 times less ATP for 1 mole of glucose metabolism. A bacterium grown with a limited amount of glucose showed a greater growth performance (bacterial dry weight/metabolite weight) under aerobic conditions than under anaerobic conditions.

Bacterial growth

Cells multiply during development. In unicellular bacteria, growth increases the number of bacteria in an inoculum. Bacteria multiply by fission. A generation is defined as a cell doubling. Generation time is the amount of time it takes to double the number of cells. Generation time varies depending on bacteria, 20 minutes in E.coli, 20-24 hours in tuberculosis.

Exponential growth

Since the two daughter cells can grow at the same rate as the parent cell, the number of cells in the intestine of the inoculum increases with time by an exponential 20, 21, 22, 23.....that is exponential growth.

The growth rate of the inoculum at a given time is proportional to the number of cells present at that time. This relationship can be expressed in the form of the following equation:

dN/dT  =  kN

Analyzing the above equation, we have:

N = N0 and kt

where N0 is the number of cells at time 0 and N is the number of cells at any time t thereafter. In equation (2), k is the development constant:

Solving the equation in terms of k we have:

k = (Ln N - Ln N0)/t

 Convert to decimal logarithms

k = 2,302 (log N - log N0) / (t2  -    t1)

Thus k represents the rate at which the natural logarithm of the number of cells increases with time and can be determined graphically.

The rate at which the natural logarithm of the cell number increases with time

Image. The rate at which the natural logarithm of the cell number increases with time.

The development path

Inoculate a liquid medium with bacteria from a previously grown inoculum that has grown to saturation, determine the number of cells in 1 ml, respectively, and plot the logarithm of the cell concentration over time. development show.

The line consists of 4 phases:

The development path

Image. The development path

A: Latent phase B: exponential phase C: stationary phase D: dead phase.

Latent Phase: This indicates the stage at which the cell begins to adapt to a new environment. Enzymes and metabolites are formed and accumulated until a concentration is reached where growth can be resumed.

Exponential phase: In this phase the growth rate is constant. All the cashew bacteria multiply at a constant rate and the average cell size is also constant.

This phenomenon is continued until one of the following two events occurs. One or more feedstuffs in the medium are deficient or toxic metabolites accumulate. For aerobic bacteria the first food that becomes limited is oxygen. At the cell concentration around 107/ml in the case of aerobic bacteria, the bacterial rate decreases if oxygen is not added to the medium by stirring or pumping air. When the cell concentration reached 4-5 x 10 9/ml the rate of diffusion of oxygen could not be satisfied even in an aerated environment and growth gradually slowed down.

Stop phase: at this stage, the shortage of food and accumulation of toxic products cause the cell count to stop completely. The bacteria reproduce less and less and the growth in mass also decreases, some cells die but are compensated by the formation of some new cells.

Dead phase: Begins after a period of time in the dormant phase, this time varies with bacterial species and culture conditions. More and more bacteria die. Normally after cell death, some cells continue to live on food released from lysed cells.

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