Water as the Basis of Vital Activity
The aqueous environment forms the overwhelming majority of the bacterial cell. Water inside the microorganism can exist in a free or bound state. The mechanical function of water is to maintain the necessary intracellular pressure (turgor), while its chemical function is to facilitate hydrolysis reactions.
When moisture is lost, metabolic processes freeze, and the cell stops multiplying. This property is widely used in practice: lyophilization (vacuum drying of a pre-frozen culture) allows strains to be preserved for a long time, as the microbe does not die but merely enters a dormant state.
Dry Residue: Proteins and Carbohydrates
The remaining 10% of the mass is formed by the microorganism's dry residue. Its composition is distributed extremely unevenly among macromolecules:
| Component | Share of Dry Residue |
|---|---|
| Proteins | 52% |
| Carbohydrates | 17% |
| RNA | 16% |
| Lipids | 9% |
| DNA | 3% |
| Minerals | 3% |
Proteins are the dominant component. They catalyze biochemical transformations (enzymatic role) and build vital cell elements: the cytoplasmic membrane, cell wall, capsules, spores, and flagella. Bacterial proteins contain unique compounds absent in human tissues, such as diaminopimelic acid and D-amino acid isomers.
Carbohydrates are represented by the full spectrum of sugars (from mono- to polysaccharides) and readily form complex bonds with lipids and proteins. They participate in cell wall construction, are stored as reserve starch and glycogen, and determine the antigenic specificity of the bacterium.
Lipids and Nucleic Acids
Lipids are concentrated in the cell wall of Gram-negative microbes and in the cytoplasmic membrane (CPM). They serve as a reserve energy source and form somatic antigens, including endotoxins (lipopolysaccharides). Long-chain acids ($C_{14}$–$C_{18}$) predominate in fat structures. Acid-fast bacteria are distinguished by a high content of waxes and mycolic acid, while Mycoplasma species are the only prokaryotes whose CPM contains sterols.
Nucleic acids are responsible for genetic information and protein synthesis:
- RNA is present in messenger, transfer, and ribosomal forms. Free nucleotides not only build polymer chains but also make up coenzymes.
- DNA consists of two antiparallel strands ($5'\rightarrow3'$ and $3'\rightarrow5'$ directions). The helix is held together by hydrogen bonds based on the principle of complementarity (adenine is complementary to thymine, guanine to cytosine). A DNA monomer consists of deoxyribose, a phosphate group, and a nitrogenous base.
Minerals and Ions
Analysis of bacterial ash reveals macroelements (nitrogen, sulfur, phosphorus, calcium, potassium, magnesium, iron) and microelements (copper, zinc, barium, cobalt).
Key organogens perform basic metabolic tasks:
- Nitrogen (N): essential for the synthesis of proteins and nucleotides.
- Sulfur (S): forms sulfhydryl groups that stabilize the spatial structure of proteins.
- Phosphorus (P): part of nucleic acid structure and ensures energy metabolism (ATP).
Metal ions act as enzyme activators (magnesium, manganese, iron) and ribosome stabilizers (potassium, magnesium). To capture and transport iron from the external environment, bacteria possess specific transport molecules called siderophores.