Microbial Structure, Metabolism, and Growth: Study Guide

Chapter 2.7 (from Unit 1): Bacterial Cell Inclusions

Overview of Bacterial Cell Inclusions

Bacterial cells contain various inclusions that serve as storage sites for nutrients and other important molecules. These inclusions play a role in the survival and adaptation of bacteria to changing environments.

• Definition: Cell inclusions are reserve deposits found in prokaryotic and eukaryotic cells, often storing nutrients or building blocks.

• Types: Common inclusions include polyphosphate granules, sulfur granules, magnetosomes, and gas vesicles.

• Functions: Storage of energy (e.g., glycogen), phosphate, sulfur, or gas for buoyancy.

• Example: Magnetosomes help bacteria orient along magnetic fields.

Chapter 2.8 – 2.11: Endospores and Motility

Endospores: Structure and Function

Endospores are highly resistant, dormant structures formed by certain bacteria to survive extreme conditions.

• Structure: Composed of a tough outer coat, cortex, and core containing DNA and essential enzymes.

• Function: Enable bacteria to withstand heat, desiccation, chemicals, and radiation.

• Formation: Sporulation is the process of endospore formation, while germination is the return to vegetative growth.

• Resistance: Endospores are resistant due to low water content, dipicolinic acid, and protective proteins.

• Example: Bacillus and Clostridium species form endospores.

Bacterial Motility

Bacteria move using various structures and mechanisms to find optimal environments.

• Flagella: Long, whip-like appendages that rotate to propel bacteria.

• Types of Motility: Swimming (flagella), twitching (pili), gliding (surface movement without flagella).

• Chemotaxis: Movement toward (attractant) or away from (repellent) chemical stimuli.

• Example: Escherichia coli uses peritrichous flagella for motility.

Chapter 5.3–5.4 (Energetics)

Microbial Growth Requirements

Microorganisms require specific nutrients and environmental conditions for growth.

• Major Nutritional Types: Based on energy and carbon sources: phototrophs (light), chemotrophs (chemicals), autotrophs (CO2), heterotrophs (organic carbon).

• Essential Elements: Carbon, nitrogen, sulfur, phosphorus, trace elements, and growth factors.

Metabolism: Catabolism and Anabolism

Metabolism encompasses all chemical reactions in a cell, divided into catabolism (breakdown) and anabolism (biosynthesis).

• Catabolism: Degradative reactions that release energy.

• Anabolism: Biosynthetic reactions that require energy input.

• Energy Coupling: Energy from catabolism is used to drive anabolic reactions.

Free Energy and Redox Reactions

Microbial metabolism relies on energy changes during chemical reactions, especially redox (oxidation-reduction) reactions.

• Free Energy Change ($\Delta G$): Indicates whether a reaction is spontaneous ($\Delta G < 0$) or requires energy input ($\Delta G > 0$).

• Standard Free Energy Change ($\Delta G^\circ'$): Free energy change under standard conditions.

• Redox Reactions: Involve electron transfer; oxidation is loss of electrons, reduction is gain of electrons.

• Redox Potential ($E_0'$): Tendency of a molecule to accept electrons; electrons flow from lower to higher $E_0'$.

• Electron Carriers: NAD+, NADP+ shuttle electrons in metabolism.

ATP in Metabolism

ATP (adenosine triphosphate) is the primary energy currency in cells.

• ATP Synthesis: Produced by substrate-level phosphorylation, oxidative phosphorylation, and photophosphorylation.

• ATP Hydrolysis: Releases energy to drive cellular processes.

• Example: Glycolysis and the electron transport chain generate ATP.

Chapter 3.6 – 3.10, 14.18 (Catabolism)

Microbial Catabolic Pathways

Microorganisms obtain energy through various catabolic processes, including fermentation, respiration, and anaerobic respiration.

• Fermentation: Anaerobic process yielding ATP and organic end products (e.g., lactic acid, ethanol).

• Aerobic Respiration: Uses oxygen as the final electron acceptor, producing more ATP.

• Anaerobic Respiration: Uses alternative electron acceptors (e.g., nitrate, sulfate).

• Homolactic vs. Heterolactic Fermentation: Homolactic produces only lactic acid; heterolactic produces lactic acid plus other products.

• Mixed Acid and Butanediol Fermentation: Different bacteria produce characteristic end products.

Electron Transport and ATP Synthesis

The electron transport chain (ETC) is a series of membrane-bound carriers that transfer electrons and generate a proton gradient for ATP synthesis.

• Location: Bacterial ETC is in the cytoplasmic membrane.

• Function: Transfers electrons from NADH/FADH2 to terminal electron acceptor, pumping protons to create a proton motive force (PMF).

• ATP Synthase: Enzyme complex that uses PMF to synthesize ATP from ADP and inorganic phosphate.

• Equation: $\text{ADP} + \text{P}_i + \text{H}^+_{\text{outside}} \rightarrow \text{ATP} + \text{H}_2\text{O} + \text{H}^+_{\text{inside}}$

Chapter 4.3 – 4.7, 4.11 – 4.16 (Growth)

Bacterial Growth and Reproduction

Bacteria reproduce primarily by binary fission, leading to exponential population growth under optimal conditions.

• Binary Fission: A single cell divides into two identical daughter cells.

• Growth Curve: Four phases: lag, log (exponential), stationary, and death.

• Measurement Methods: Direct (microscopic count, plate count) and indirect (turbidity, dry weight).

• Advantages/Disadvantages: Plate counts are accurate but time-consuming; turbidity is rapid but less precise.

Microbial Growth Patterns

• Colony Morphology: Shape, size, color, and texture of colonies can help identify microorganisms.

• Environmental Effects: Temperature, pH, osmolarity, and oxygen availability affect growth.

• Biofilms: Communities of microorganisms attached to surfaces, protected by extracellular matrix.

Diseases (Selected Topics)

Overview of Infectious Diseases

Microorganisms can cause diseases in humans and other organisms. Understanding their transmission and symptoms is crucial for prevention and treatment.

• Causes: Bacteria, viruses, fungi, and parasites.

• Pathogen Identification: Based on Gram reaction, DNA/RNA type, and shape.

• Transmission Routes: Direct contact, airborne, vector-borne, etc.

• Symptoms: Vary by disease; may include fever, rash, cough, etc.

Summary Table: Key Metabolic Pathways

Pathway	Oxygen Required?	ATP Yield (per glucose)	End Products
Glycolysis	No	2	Pyruvate, ATP, NADH
Aerobic Respiration	Yes	~38	CO2, H2O, ATP
Anaerobic Respiration	No	Varies (<38)	CO2, reduced inorganic compounds, ATP
Fermentation	No	2	Lactic acid, ethanol, CO2, other organics

Additional info: The above notes are based on a course outline/syllabus for a college-level microbiology course, summarizing key learning objectives and topics for exam preparation. For further study, refer to the recommended textbook chapters and online resources provided in the syllabus.