Microbial Metabolism

Overview of Metabolism

Metabolism encompasses all chemical reactions occurring within a microorganism. These reactions are organized into metabolic pathways, where enzymes catalyze stepwise conversions from substrates to final products.

• Catabolism: The breakdown of molecules to release energy (exergonic reactions).

• Anabolism: The synthesis of complex molecules (e.g., DNA, proteins) requiring energy input (endergonic reactions).

• ATP (Adenosine Triphosphate): The primary energy currency of the cell, generated mainly through catabolic pathways and consumed during anabolic processes.

• Energy Coupling: The process by which energy released from ATP hydrolysis drives endergonic cellular work.

• Phosphorylation: The transfer of a phosphate group from ATP to a target molecule, often altering protein activity or conformation.

Redox Reactions and Electron Carriers

Redox (reduction-oxidation) reactions involve the transfer of electrons between molecules:

• Oxidation: Loss of electrons (LEO: Lose Electrons = Oxidation).

• Reduction: Gain of electrons (GER: Gain Electrons = Reduction).

• Electron Carriers: NADH and FADH2 shuttle electrons during catabolism; NADPH is primarily used in biosynthetic (anabolic) reactions.

Enzymes and Regulation

• Enzymes: Biological catalysts that lower activation energy, increasing reaction rates. Their activity is influenced by temperature, pH, and substrate concentration.

• Inhibition: Competitive inhibitors bind the active site; noncompetitive inhibitors bind elsewhere, altering enzyme function.

• Feedback Regulation: Negative feedback occurs when the final product inhibits an early pathway step; positive feedback stimulates the pathway.

Aerobic Respiration

Aerobic respiration is a highly efficient process for ATP production, involving several stages:

• Glycolysis

• Pyruvate oxidation

• Krebs cycle (Citric Acid Cycle)

• Electron Transport Chain (ETC) and Chemiosmosis (where most ATP is generated)

Microbial Nutrition and Growth

Microbial Nutritional Types

Microbes are classified based on their energy, electron, and carbon sources:

• Energy Source: Phototrophs (light) vs. Chemotrophs (chemical compounds)

• Electron Source: Lithotrophs (inorganic) vs. Organotrophs (organic)

• Carbon Source: Autotrophs (CO2 fixation) vs. Heterotrophs (organic carbon)

Oxygen Requirements

• Obligate Aerobes: Require oxygen (grow at the top of test tube).

• Facultative Anaerobes: Grow with or without oxygen (denser at top).

• Microaerophiles: Require low oxygen (thin band below surface).

• Obligate Anaerobes: Cannot tolerate oxygen (grow at bottom).

• Aerotolerant Anaerobes: Tolerate but do not use oxygen (even growth).

Reactive Oxygen Species (ROS) and Defenses

• ROS: Superoxide (O2-), hydrogen peroxide (H2O2).

• Defenses: Superoxide dismutase (SOD), catalase, and peroxidase detoxify ROS.

Other Growth Factors

• Growth Factors: Essential nutrients microbes cannot synthesize (fastidious organisms require many).

• Temperature Groups: Psychrophiles (cold), psychrotrophs, mesophiles (moderate), thermophiles (hot), hyperthermophiles (very hot).

• Salt Tolerance: Nonhalotolerant, halotolerant, halophiles, extreme halophiles.

Culturing Microorganisms

• Media Types: Agar (solid), broth (liquid).

• Aseptic Technique: Prevents contamination.

• Pure Culture: Derived from a single colony.

• Inoculum: Material used to start a culture.

• Media Classification: Chemically defined, complex, selective (e.g., MacConkey), differential (e.g., blood agar), enrichment, reducing (for anaerobes).

Microbial Growth Curve

• Phases: Lag → Log (exponential) → Stationary → Death.

• Generation Time: Time required for population to double.

• Measuring Growth: Direct counts, plate counts/CFU (colony-forming units), membrane filtration, biomass (spectrophotometer absorbance), pellet weight.

Characterizing and Classifying Eukaryotes

Overview

Eukaryotic microorganisms include protozoa, fungi, algae, and water molds. They are classified based on cellular structure, organelles, and modes of reproduction.

Protozoa

• Alveolate-Apicomplexans: Protozoans with alveoli (membrane-bound cavities). Many use schizogony (multiple fission) and possess special organelles at their apices. Examples: Toxoplasmosis, Plasmodium, Cryptosporidium.

• Amoeba: Characterized by lobe-shaped pseudopods for movement. Free-living, do not form aggregates. Examples: Entamoeba, Naegleria.

• Euglena: Photoautotrophic, single-celled organisms with chloroplasts and disc-shaped mitochondrial cristae. Store food as paramylon, possess a flexible pellicle, eyespot, and flagellum.

• Giardia: Belongs to Diplomonadida; lacks mitochondria, peroxisomes, and Golgi bodies but has mitosomes. Has two nuclei and multiple flagella. Causes diarrhea and bloating when ingested as cysts.

• Trypanosoma: Includes species causing Chagas disease (Trypanosoma cruzi, transmitted by kissing bug) and African sleeping sickness (Trypanosoma brucei, transmitted by tsetse fly).

• Trichomonas: Trichomonas vaginalis causes trichomoniasis (STD). In females, leads to yellow-green discharge and irritation; males may be asymptomatic. Example of a kinetoplastid.

• Leishmania: Another kinetoplastid, causes cutaneous, mucocutaneous, and visceral leishmaniasis. Transmitted by sand fly.

Table: Major Protozoan Groups and Features

Microbial Diseases of the Skin and Wounds

Necrotizing Fasciitis (Group A Streptococcus)

Necrotizing fasciitis is a severe infection characterized by rapid tissue destruction. Symptoms include redness, intense pain, swelling, and eventual discoloration and distension of the skin over affected muscles. Early symptoms are nonspecific, making diagnosis challenging. Complete removal of affected tissue is necessary for treatment.

Pseudomonas Infection

Pseudomonas infections often occur when burns or wounds expose underlying tissues, allowing this opportunistic pathogen to invade. Bloodstream invasion can cause fever, chills, and shock. The presence of pyocyanin pigment is a diagnostic indicator of Pseudomonas infection.

Impetigo

Impetigo presents as small, red patches on the skin that develop into oozing, pus-filled vesicles, which then form honey-colored crusts. Staphylococcus aureus is responsible for 80% of cases. The infection spreads through skin breaks and is highly contagious via direct contact.

Additional Info

• The provided table of contents (image_11) confirms coverage of Chapter 12: Characterizing and Classifying Eukaryotes, including protozoa, fungi, algae, and water molds, aligning with the notes above.