Study Notes for BIOL211 - Microbial Metabolism

BIOL211 – Fundamentals of Microbiology

Introduction

  • Instructor: Dr/Professor Mercado

  • Term: Fall 2025

  • Interactive Learning Tool: Join Poll Everywhere with username sdsumicrobes and sign in with SDSU email.

Chapter 8: Microbial Metabolism

  • Date: October 8th, 2025

Learning Objectives

  • Define metabolism and its relevance to all living organisms.

  • Define an enzyme and understand their role in metabolic reactions.

  • Distinguish between exergonic and endergonic reactions.

  • Identify the inputs and products of cellular respiration.

  • Distinguish between anaerobic and aerobic organisms.

  • Characterize the growth kinetics of microbes, focusing on specific phases of growth.

Metabolism: Exergonic and Endergonic Reactions

  • Energy Requirement: All living organisms require energy to function.

  • Definition: Metabolism is the generation and use of energy.

  • Energy Flow: Metabolism involves the release and use of energy.

Cellular Energy Conversion

  • Energy Conversion:

    • Cells convert the energy contained in biological molecules into adenosine triphosphate (ATP).

    • ATP Significance: ATP functions as the cell's energy currency.

  • Phosphate Role: Phosphate groups in ATP store energy; when phosphate is removed, energy is released (reaction: ext{ATP}
    ightarrow ext{ADP} + ext{P}_i).

  • ATP Demand: Cells require a substantial amount of ATP to carry out metabolic functions.

Redox Reactions and Electron Carriers

  • Energy and Electrons: The energy in molecules is closely linked to their electrons.

  • Oxidation and Reduction:

    • Molecules that lose electrons undergo oxidation.

    • Molecules that gain electrons undergo reduction.

  • Biological Relevance: Redox reactions are pivotal as biological molecules are broken down to release energy.

  • Electron Carriers:

    • NAD+ (oxidized)/NADH (reduced)

    • FAD+ (oxidized)/FADH2 (reduced)

Cellular Respiration Overview

  • General Reaction: ext{Glucose} + 6 ext{ O}2 ightarrow 6 ext{ CO}2 + 6 ext{ H}_2 ext{O}

    1. Mass Transformation: Conversion of Glucose and O2 to CO2 and H2O.

    2. Energy Transformation: Conversion of chemical bonds of glucose to the bonds of ATP.

  • Energy Source: ATP is derived from cellular respiration, converting energy from food into ATP.

  • Aerobic Respiration: This process occurs in the presence of oxygen.

Stages of Cellular Respiration

1. Glycolysis

  • Process: Breakdown of glucose into pyruvate.

  • Location: Occurs in the cytoplasm of cells.

  • Inputs: Glucose and ATP.

  • Outputs: Pyruvate, ATP, and NADH.

2. Citric Acid Cycle (Krebs Cycle)

  • Process Overview: Completes the oxidation of pyruvate, releasing CO2, NADH, FADH2, and ATP.

  • Location:

    • Eukaryotes: Mitochondrial matrix

    • Prokaryotes: Cytoplasm

  • Inputs: Acetyl-CoA.

  • Outputs: NADH, FADH2, ATP, and CO2.

3. Electron Transport Chain (Oxidative Phosphorylation)

  • Final Stage: Oxidation of NADH and FADH2, yielding most of the ATP.

  • Location:

    • Eukaryotes: Mitochondrial membrane

    • Prokaryotes: Plasma membrane

  • Inputs: All NADH and FADH2.

  • Outputs: Primarily ATP.

4. ATP Generation via Chemiosmosis

  • Mechanism: Protons (H+) move across the membrane creating a concentration gradient.

  • Function: This gradient forces protons into ATP synthase, converting ADP to ATP, a process termed oxidative phosphorylation.

Types of Cellular Respiration

Aerobic vs. Anaerobic

  • Aerobic Respiration: Relies on oxygen as the final electron acceptor.

  • Anaerobic Respiration: Operates without oxygen, utilizing alternative electron acceptors such as nitrate, carbon dioxide, or sulfate.

    • Example: Methanogens are microbes using carbon dioxide to produce methane.

Fermentation

  • Process: If cells rely solely on glycolysis, fermentation occurs to regenerate NAD+ from pyruvate.

  • Byproducts: Production of waste products such as lactate or ethanol.

  • Types:

    • Alcohol Fermentation: Conducted by yeast to produce beverages and baked goods.

    • Lactic Acid Fermentation: Performed by bacteria to produce yogurt.

Autotrophic Characteristics

  • Definition: Autotrophs produce their own energy using inorganic materials.

  • Types:

    • Phototrophs: Convert light energy into ATP.

    • Chemotrophs: Utilize chemical energy for metabolism.

Photosynthesis in Phototrophs

  • Stages:

    1. Light Reactions: Utilize sunlight to generate ATP and reduce NADP+ to NADH, acting as an electron and hydrogen carrier.

    2. Calvin Cycle: ATP and NADPH from light reactions are used to convert CO2 into sugar.

Chemoautotrophs

  • Function: Use CO2 as a carbon source and rely on reduced compounds (e.g., ammonia (NH₃), methane (CH₄), hydrogen sulfide (H₂S)).

  • Significance: They play vital roles in nutrient cycling by utilizing waste products from anaerobic prokaryotes.

Microbial Growth

  • Definition: Increase in microbial population size.

  • Mechanism: Bacteria and archaea grow through binary fission.

    • Process: A single parent cell divides into two new cells, allowing exponential growth under favorable conditions.

  • Exponential Growth: Population doubles with each cell division.

  • Generation Time: Time interval between successive divisions.

Bacterial Growth Curve

  • Phases of Growth:

    1. Lag Phase: Initial adjustment period with no significant growth.

    2. Log Phase: Rapid cell division and growth.

    3. Stationary Phase: Growth rate slows as resources deplete and waste accumulates.

    4. Death Phase: Decline in population as conditions worsen.

Growth Conditions for Bacteria

  • Fastidious Microbes: Have complex nutritional requirements, needing specific media to grow.

  • Non-Fastidious Organisms: Can grow on minimal media containing basic nutrients.

Oxygen Requirements for Bacteria

Bacterial Oxygen Tolerance Types

  • Obligate Aerobes: Require oxygen; catalase-positive.

  • Obligate Anaerobes: Cannot tolerate oxygen; catalase-negative.

  • Facultative Anaerobes: Prefer oxygen but can also grow anaerobically; catalase-positive.

  • Aerotolerant Anaerobes: Tolerate oxygen but do not use it; catalase-positive.

  • Microaerophiles: Need small amounts of oxygen; produce low catalase levels.

Other Growth Conditions Affecting Bacteria

Effects of Temperature

  • Each microbe has a specific growth temperature range, identifying its optimal growth temperature (e.g., human body temperature).

Effects of pH on Bacterial Growth

  • pH Scale: Measures acidity or basicity (H+ ion concentration).

  • Examples:

    • Battery acid: pH 0 (Acidic)

    • Stomach acid: pH 1

    • Lemon juice: pH 2

    • Vinegar: pH 3

    • Tomato juice: pH 4

    • Black coffee: pH 5

    • Saliva: pH 6 (Neutral)

    • Distilled water: pH 7 (Neutral)

    • Seawater: pH 8

    • Borax: pH 9

    • Milk of magnesia: pH 10

    • Ammonia: pH 11

    • Soapy water: pH 12

    • Oven cleaner: pH 13

    • Drain cleaner: pH 14 (Basic)

Effects of Nutritional Requirements

  • Halophiles: Bacteria that thrive in high salt concentrations promote unique growth conditions.

  • Nutrient Availability: Abundance of nutrients (like sugars, vitamins, and trace metals) can substantially impact bacterial species growth.