Biochemical Pathways and Microbial Metabolism: Syllabus Overview and Study Guide

Biochemical Pathways and Microbial Metabolism

Course Overview

This course provides an in-depth understanding of the role of microbes in the synthesis and degradation of biomolecules, focusing on central metabolic pathways, lipid metabolism, nitrogenous compound metabolism, and hydrocarbon metabolism. It is designed for postgraduate students with introductory knowledge of metabolic pathways.

Unit 1: Central Metabolic Pathways and Regulation

Overview

This unit explores the primary metabolic pathways in microorganisms, their regulation, and the utilization of various sugars and complex polysaccharides. It also covers the synthesis of important cellular components and various fermentation processes.

• Glycolysis: The breakdown of glucose to pyruvate, generating ATP and NADH. Central to energy production in cells.

• Pentose Phosphate Pathway (PPP): Generates NADPH and pentoses; important for biosynthetic reactions.

• Entner-Doudoroff (ED) Pathway: An alternative to glycolysis found in some bacteria, producing pyruvate and glyceraldehyde-3-phosphate.

• Citric Acid Cycle (TCA/Krebs Cycle): Oxidizes acetyl-CoA to CO2, generating NADH, FADH2, and ATP.

• Branched and Reverse TCA Cycles: Variations in the TCA cycle for biosynthetic and energy needs, including the glyoxylate cycle for utilizing two-carbon compounds.

• Utilization of Sugars Other Than Glucose: Pathways for metabolizing alternative sugars and complex polysaccharides.

• Synthesis of Peptidoglycans and Glycoproteins: Essential for cell wall structure and function in bacteria.

• Fermentation Pathways:

  • Ethanol Fermentation: Conversion of pyruvate to ethanol and CO2 (e.g., Saccharomyces cerevisiae).

  • Lactate Fermentation: Production of lactic acid from pyruvate (e.g., Lactobacillus species).

  • Butyrate, Butanol-Acetone, Mixed Acid, 2,3-Butanediol, Propionate, Succinate, Acetate, Methane: Various fermentation end-products depending on microbial species and environmental conditions.

Example: The glyoxylate cycle enables bacteria and plants to convert fatty acids into carbohydrates, bypassing the decarboxylation steps of the TCA cycle.

Unit 2: Lipids Metabolism

Overview

This unit examines the composition, biosynthesis, and degradation of lipids in microorganisms, including the accumulation of lipids and the metabolism of hydrocarbons.

• Lipid Composition of Microorganisms: Includes phospholipids, glycolipids, and storage lipids such as triacylglycerols.

• Biosynthesis and Degradation of Lipids: Pathways for fatty acid synthesis (e.g., fatty acid synthase complex) and β-oxidation for degradation.

• Lipid Accumulation in Yeasts: Some yeasts accumulate lipids as energy reserves, important for industrial applications.

• Hydrocarbon Utilization: Microbes can metabolize hydrocarbons as carbon and energy sources.

• Polyhydroxyalkanoates (PHA) Synthesis and Degradation: PHAs are biodegradable polymers produced by bacteria as carbon storage materials.

• Poly-β-hydroxybutyrate (PHB) Production: A type of PHA with applications in bioplastics.

Example: Cupriavidus necator is a bacterium known for efficient PHB production under nutrient-limited conditions.

Unit 3: Metabolism of Organic Nitrogenous Compounds

Overview

This unit covers the biosynthesis and catabolism of amino acids, polyamines, and nucleic acids in microorganisms, including key metabolic pathways and regulatory mechanisms.

• Biosynthesis of Amino Acids:

  • Oxaloacetate and Pyruvate Families

  • Phosphoglycerate Family

  • α-Oxoglutarate Family

  • Aromatic Amino Acids and L-Histidine Synthesis

• Polyamine Biosynthesis and Regulation: Polyamines (e.g., putrescine, spermidine) are important for cell growth and function.

• Urea Cycle: Pathway for the disposal of excess nitrogen in some microorganisms.

• Catabolism of Amino Acids: Includes transamination, decarboxylation, and oxidative deamination reactions.

• Nucleic Acid Metabolism:

  • Biosynthesis and Catabolism of Purine and Pyrimidine Nucleotides

  • Ribonucleotide Reductase (RNR): Converts ribonucleotides to deoxyribonucleotides for DNA synthesis.

Example: The conversion of glutamate to α-ketoglutarate via oxidative deamination is a key step in amino acid catabolism.

Unit 4: Hydrocarbon Metabolism and Endogenous Metabolism

Overview

This unit focuses on the microbial metabolism of aromatic and aliphatic hydrocarbons, the role of oxygenases in ring cleavage, and the utilization of secondary metabolites for industrial and medical applications.

• Microbial Metabolism of Hydrocarbons: Includes degradation of compounds like camphor and 2,4-D (herbicide) by monooxygenases and dioxygenases.

• Ring Cleavage Mechanisms: Ortho and meta-cleavage pathways for aromatic ring breakdown.

• Reductive Catabolism: Anaerobic degradation of hydrocarbons.

• Secondary Metabolism: Production of vitamins, toxins (e.g., aflatoxin, corynebacterial toxins), hormones (e.g., gibberellic acid), and antibiotics (e.g., penicillin, streptomycin).

• Microbial Growth on C1 Compounds: Utilization of single-carbon compounds (e.g., methane, methanol) as energy sources.

Example: Pseudomonas putida can degrade aromatic hydrocarbons via the ortho-cleavage pathway, making it useful in bioremediation.

Summary Table: Course Units and Key Topics

Unit	Main Topics	Key Processes/Examples
1	Central Metabolic Pathways and Regulation	Glycolysis, PPP, ED pathway, TCA cycle, Fermentation
2	Lipids Metabolism	Lipid biosynthesis/degradation, PHB production
3	Metabolism of Organic Nitrogenous Compounds	Amino acid/nucleotide metabolism, Urea cycle
4	Hydrocarbon and Endogenous Metabolism	Hydrocarbon degradation, Secondary metabolites

Additional info: This syllabus aligns with topics from Ch. 5 (Microbial Metabolism), Ch. 6 (Microbial Nutrition and Growth), and related chapters on microbial biochemistry and physiology.