Nutrition and Bacterial Metabolism - Chapter III

Chapter III: Nutrition and Bacterial Metabolism

• This chapter covers nutrition and bacterial metabolism.
• It is a 2nd-year Natural Sciences topic.

Part 1: Bacterial Nutrition

• Discusses the nutritional needs of bacterial cells.
• Diagrams and chemical formulas are presented illustrating the bacterial cell and needed components.

Nutritional Requirements

• Nutrients are essential chemical compounds for bacteria.
• These components are used for energy production, metabolic processes, growth, and reproduction.
• Nutrients act as essential constituents of cellular material, supporting enzyme and transport systems, and providing components for usable biological energy.

Definition of Nutrients

• Nutrients are essential chemical compounds for energy, metabolism, growth, and reproduction in bacteria.
• They act as constituents of cellular materials.
• Support enzyme and transport system activities.
• Provide components for biologically usable energy.

Chemical Composition of a Bacterial Cell

• Bacterial cells are composed of water (80-90%) and dry matter (10%).
• Dry matter consists of proteins (52%), polysaccharides (17%), lipids (9%), RNA (16%), and DNA (3%).

Types of Nutrients

• Macronutrients, Micronutrients, and Growth Factors

a) Macronutrients

• Required in large amounts for bacterial growth and metabolism.
• Include carbon (C), nitrogen (N), oxygen (O), hydrogen (H), phosphorus (P), and sulfur (S).

1- Carbon (C)

• Most abundant constituent element in bacteria (50% of dry cell weight).
• Essential for synthesizing cellular materials (carbohydrates, lipids, proteins, nucleic acids).
• Serves as a main energy source for bacterial growth and metabolism.
• Bacteria can obtain carbon from inorganic (CO₂) or organic sources, depending on their type.
  • Autotrophs use inorganic carbon.
  • Heterotrophs use organic carbon.

2- Nitrogen (N)

• Makes up 14% of dry cell weight.
• Needed for synthesizing amino acids (proteins), nucleotides (DNA, RNA), and other nitrogen-containing compounds.
• Found in inorganic forms (e.g., ammonium, nitrate) and organic forms (e.g., amino acids, peptides).
• Nitrogen-fixing bacteria obtain nitrogen from the atmosphere (N₂).

3- Phosphorus (P)

• A key component of nucleic acids (DNA, RNA), ATP (energy currency), and phospholipids in cell membranes.
• Bacteria absorb phosphorus as phosphate ions (PO₄³⁻) from their surroundings.

4- Sulfur (S)

• Necessary for synthesizing certain amino acids (e.g., cysteine, methionine), vitamins (e.g., biotin, thiamine), and growth factors (e.g., coenzyme A).
• Bacteria obtain sulfur from sulfate (SO₄²⁻) or organic sulfur compounds.

5- Oxygen (O) and Hydrogen (H)

• Oxygen is needed for aerobic respiration in many bacteria as the final electron acceptor in the electron transport chain.
• However, some bacteria are anaerobic and don't need oxygen.
• Hydrogen is involved in maintaining cellular pH balance and is a part of water and organic molecules.

b) Micronutrients

• Required in smaller amounts for bacterial growth.
• Include trace elements like calcium (Ca²⁺), magnesium (Mg²⁺), potassium (K⁺), iron (Fe²⁺), magnesium (Mg), and zinc (Zn).

1- Calcium (Ca²⁺)

• Plays a role in cell wall stability.
• A cofactor for certain enzymes (e.g., proteases).
• Implicated in gene expression, chemotaxis, sporulation, and biofilm formation.

2- Magnesium (Mg²⁺)

• Essential for stabilizing nucleic acids, ribosomes, and cell membranes.
• A cofactor for many enzymes (including ATPases and DNA polymerases).
• A component of bacterial chlorophyll pigments.

3- Potassium (K⁺)

• Acts as a cofactor for many enzymes.
• Involved in regulating pH within the cell.

4- Iron (Fe)

• Crucial cofactor for many enzymes participating in metabolic pathways (electron transport, DNA synthesis, and cellular respiration).

5- Zinc (Zn)

• Vital cofactor for numerous enzymes, essential for DNA replication (DNA polymerase) and protein synthesis (ribosomal enzymes).

6- Manganese (Mn)

• A cofactor for enzymes involved in oxidative stress defense.
• Essential for amino acid and carbohydrate production.

7- Other micronutrients

• Molybdenum (Mo): component of molybdoenzymes involved in nitrogen fixation (e.g., nitrate reductase).
• Copper (Cu): plays a role in respiration, iron acquisition, and oxidative stress defense.
• Cobalt (Co): needed by some bacteria for B12 (cobalamin) biosynthesis.
• Selenium (Se): part of selenoproteins, involved in redox reactions, and protecting bacteria against oxidative stress.

Roles of Micronutrients in Bacterial Cells

• Integral to bacterial survival and function in several ways:
• Enzyme activation and function (cofactors).
• Electron transfer and respiration (e.g., electron transport chains, ATP generation).
• DNA and RNA synthesis, metabolism, and energy production.
• Oxidative stress protection (antioxidant enzymes).

c) Growth Factors

• Organic compounds some bacteria can't synthesize and must obtain from the environment.
• Needed in small quantities.
• Include vitamins (e.g., B vitamins, vitamin K), amino acids, proteins, and nucleic acid-like compounds (purines, pyrimidines).
• "Fastidious bacteria" require many growth factors.

II. Energy Requirements

• Phototrophic bacteria use light as an energy source (photosynthesis).

  • Different types: Cyanobacteria, Green Sulfur Bacteria, Purple Sulfur Bacteria.

• Chemotrophic bacteria obtain energy from chemical compounds.

  • Chemoorganotrophs use organic compounds (sugars, amino acids).
  • Lithotrophs use inorganic compounds (hydrogen gas, sulfur, iron).

III. Nutritional Types of Bacteria

• Photoautotrophs: use light for energy and CO₂ as a carbon source.
• Photoheterotrophs: use light for energy and organic compounds as a carbon source.
• Chemoautotrophs: obtain energy by oxidizing inorganic compounds, with CO₂ as the carbon source.
• Chemoheterotrophs: obtain energy and carbon from organic compounds.