Microbial Metabolism

Laboratory Culture of Microorganisms

Microorganisms require specific nutrients and conditions for growth, which are provided in laboratory culture media. Understanding the chemistry and nutrition of microbial growth is essential for cultivating and studying microbes.

• Nutrients: Substances that supply monomers or precursors required by cells for growth and metabolism.

• Macronutrients: Nutrients required in large amounts, essential for the synthesis of cellular components.

• Micronutrients: Nutrients required in trace amounts, often serving as cofactors for enzymatic reactions.

Macronutrients

Macronutrients are the primary elements and compounds needed in significant quantities for microbial growth and function.

• Carbon (C): Required by all cells; major element in all classes of macromolecules. Typical bacterial cell is ~50% carbon by dry weight. Heterotrophs use organic carbon, while autotrophs use carbon dioxide (CO2).

• Nitrogen (N): About 13% of a bacterial cell's dry weight. Essential for proteins, nucleic acids, and other cell constituents.

• Phosphorus (P): Required for synthesis of nucleic acids and phospholipids.

• Sulfur (S): Found in sulfur-containing amino acids (cysteine and methionine), vitamins (thiamine, biotin, lipoic acid), and coenzyme A.

• Potassium (K): Required by enzymes for activity.

• Magnesium (Mg): Stabilizes ribosomes, membranes, and nucleic acids; also required for many enzymes.

• Calcium (Ca): Helps stabilize cell walls in microbes; plays a key role in heat stability of endospores.

• Sodium (Na): Required by some microbes, such as marine microorganisms.

Micronutrients

Micronutrients are required in much smaller amounts but are still essential for microbial metabolism.

• Iron (Fe): Key component of cytochromes and FeS proteins involved in electron transport.

• Growth Factors: Organic compounds required in small amounts by certain organisms. Examples include vitamins, amino acids, purines, and pyrimidines.

• Vitamins: Most commonly required growth factors; most function as coenzymes.

Elemental Composition of Microbial Cells

The elemental composition of microbial cells reflects the importance of various nutrients in cellular structure and function. The periodic table can be used to classify elements based on their necessity for microorganisms.

Example: An E. coli cell is composed of approximately 50% carbon, 20% oxygen, 13% nitrogen, 8% hydrogen, 3% phosphorus, 2% sulfur, and 0.5% other elements by dry weight.

Media and Laboratory Culture

Culture media are nutrient solutions used to grow microbes in the laboratory. They are classified by their chemical composition and application.

• Defined Media: Precise chemical composition is known.

• Complex Media: Composed of digests of chemically undefined substances (e.g., yeast and meat extracts).

• Enriched Media: Contain complex media plus additional nutrients for nutritionally demanding organisms.

• Selective Media: Contain compounds that selectively inhibit growth of some microbes but not others.

• Differential Media: Contain an indicator, usually a dye, that detects particular chemical reactions occurring during growth.

Pure Culture Techniques

Obtaining pure cultures is essential for studying the properties of individual microbial species.

• Pure Culture: A culture containing only a single kind of microbe.

• Contaminants: Unwanted organisms in a culture.

• Cells can be grown in liquid or solid culture media. Solid media are prepared by addition of a gelling agent such as agar or gelatin.

• When grown on solid media, cells form isolated masses called colonies.

Additional info: The periodic table shown in the notes categorizes elements based on their essentiality for microorganisms, which is important for understanding microbial nutrition and laboratory media formulation.