GENERAL MICROBIOLOGY - T.P. Pyrog - 2004

4. CHEMICAL COMPOSITION OF THE BACTERIAL CELL

4.4. PHYSICOCHEMICAL PROPERTIES OF THE BACTERIAL CELL

The combination of physicochemical properties depends on the species Characteristics of Bacteria, their age, and cultivation conditions.

Brownian motion. Characteristic of non-motile bacteria smaller than 4 µm. This phenomenon can be suppressed by adding electrolytes or colloids to nutrient media.

Refractive index. Determined by placing bacteria into solutions with various refractive indices. Under Cell/15.html">Microscopy, bacteria become invisible when the refractive index of The Cell matches that of the medium. For example, Vibrio cholerae becomes invisible in phenol with a refractive index of 1.55.

Density of the microbial cell. It depends on age, bacterial species, and medium composition. Staphylococcus aureus has a density of 1.118, and Escherichia coli — 1.094.

Viscosity of the microbial cell. On average, it exceeds the viscosity of Water by 800 times (comparable to the viscosity of glycerol). To determine intracellular viscosity, a metal plate is inserted into the Cytoplasm using a micromanipulator. The intensity of its movement indicates the magnitude of viscosity. The intensity of an electromagnetic field causing the movement of an identical plate in water serves as a control.

Elasticity is the ability of a cell to restore its shape after temporary deformations.

Electrical surface charge of bacteria. In an electric field, bacteria move toward the cathode (cataphoresis) or the anode (anaphoresis), or cease movement at certain pH values (isoelectric point). Most bacteria carry a negative charge.

Redox potential (Eh). Expressed in volts (V). Aerobic microorganisms grow in media with an Eh of +0.2...0.4 V (at neutral pH). They easily alter Eh due to a well-developed redox enzyme system (cytochrome oxidase, catalase, etc.). Anaerobic bacteria cannot grow if the medium's Eh exceeds 0.2 V.

Structure/106.html">Hydrophobicity and hydrophilicity. Determined by the presence of corresponding chemical groups in surface structures: hydrophilic — OH, NH₂, SO₃, COOH, NH₃, — C = 0; hydrophobic — CH₃, C₆H₅, and others. Most bacteria are hydrophilic, whereas acid-fast bacilli are hydrophobic.

Nonspecific agglutination (clumping). When growing bacteria in liquid nutrient media, either a uniform turbidity of the medium is observed, or a sediment forms with a more or less transparent supernatant above it. In the latter case, bacterial agglutination occurs. It depends on A number of factors: the degree of Hydration of polar ionizing and non-ionizing groups, The amount of salts and ions adsorbed on the cell surface, and the electrical charge.

Ion adsorption. The intensity of ion penetration into the cell is determined by their position in the cationic and anionic series:

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This means that the solubility of salts of a specific cation decreases due to the action of another salt whose cation is located to the right. Thus, permeability to lithium salts decreases in the presence of magnesium, barium, and calcium salts. In the anionic series, permeability is greater the further to the left the ion is positioned. For instance, permeability to the chloride anion is lower than to bromide.

Osmotic pressure. Due to the presence of A large number of free electrolytes in the cell, the internal pressure is high. Some bacteria (halophilic) are able to withstand high internal pressure and are referred to as osmophilic.

Luminescent bacteria. All light-emitting organisms share the same nature of luminescence — their Bioluminescence represents a chemical reaction catalyzed by a specific enzyme. Bioluminescence is The oxidation of the substrate luciferin in the presence of the enzyme luciferase. This generates a large amount of energy that transitions the intermediate product into an excited state.