Untitled Quiz

Microbiology History: Key Figures

• Antonie van Leeuwenhoek (1670s) was the first to observe microorganisms, termed "animalcules," using a single-lens microscope.
• Louis Pasteur (1850s-60s) disproved spontaneous generation with swan-neck flask experiments and developed pasteurization to kill microbes in food and liquids.
• Robert Koch (1870s-80s) developed Koch's Postulates, linking specific microbes to diseases, such as Bacillus anthracis causing anthrax.
• Joseph Lister (1860s) pioneered antiseptic techniques to prevent infection during surgery.
• Edward Jenner (1796) developed the first vaccine for smallpox.

Germ Theory of Disease

• Microorganisms are the cause of infectious diseases.
• It led to the development of aseptic techniques, vaccines, and antibiotics.

Bacterial Cell Components and Their Functions

• Cell Wall provides shape and protection from osmotic pressure.
• Gram-positive bacteria have a thick peptidoglycan layer in their cell wall.
• Gram-negative bacteria have a thin peptidoglycan layer and an outer membrane in their cell wall.
• Plasma Membrane is selectively permeable and controls transport and is found in all bacteria.
• Ribosomes, made of 30S and 50S subunits (total 70S), are used for protein synthesis and are targeted by antibiotics like tetracyclines.
• Nucleoid is the region where circular, double-stranded bacterial DNA is located, without a nucleus.
• Flagella are used for movement, specifically chemotaxis, as seen in Escherichia coli.
• Pili and Fimbriae are used for attachment and conjugation (gene transfer), as seen in Neisseria gonorrhoeae.
• Capsule protects against the immune system (phagocytosis), exemplified by Streptococcus pneumoniae.

Bacterial Size and Shapes

• Cocci, spherical bacteria, include Staphylococcus (clusters) and Streptococcus (chains).
• Bacilli, rod-shaped bacteria, include E. coli (single rods) and Bacillus (chains).
• Spirilla, spiral-shaped bacteria, include Helicobacter pylori, which causes ulcers.

Microbial Growth in Nutrient-Rich Environments

• Bacteria grow exponentially when nutrients are abundant, doubling their population at a constant rate.
• Bacterial growth follows the equation Nt=N0×2(t/G).
• Nt represents the population at time t.
• N0 represents the initial population.
• G represents the generation time (time required for one division).
• Generation Time (G) is the time it takes for a bacterial population to double.
• G can be calculated using the formula G = t/n, where t is the total time and n is the number of generations.

Phases of the Microbial Growth Curve

• Lag Phase: No division occurs as cells adjust to the environment.
• Log (Exponential) Phase: Rapid division and optimal metabolism occur, making it the best time for antibiotic treatment.
• Stationary Phase: Nutrients deplete, waste accumulates, and the growth rate equals the death rate.
• Death Phase: Cells die faster than they divide due to toxic conditions.

Microbe of the Day: Streptomyces

• Gram-positive, filamentous bacteria are found in soil.
• It’s a major antibiotic producer, such as streptomycin and tetracycline.
• It forms spores and produces secondary metabolites.

Primary vs. Secondary Metabolism

• Primary Metabolism is essential for growth, including the production of DNA, RNA, proteins, and ATP.
• Secondary Metabolism is not needed for growth, occurring in the stationary phase, and includes the production of antibiotics (penicillin) and toxins.

Quorum Sensing

• Allows bacteria to detect population density and alter behavior when numbers are high using autoinducers (signaling molecules).
• Examples: biofilm formation (Pseudomonas aeruginosa), virulence activation (Vibrio cholerae), and light production (Vibrio fischeri in squid).

Environmental Constraints on Microbial Growth

• Bacteria follow a predictable growth curve in a closed system with limited nutrients.
• Cells are metabolically active but not dividing in the Lag Phase,
• Bacteria adjust to the environment and prepare for replication.

Log (Exponential) Phase

• There is rapid binary fission, with the population doubling at a constant rate.
• Cells are most sensitive to antibiotics during this phase because they target actively dividing cells.

Stationary Phase

• Nutrient depletion and waste accumulation slow growth.
• Cell division equals cell death, and metabolism shifts to secondary metabolites like antibiotics.

Death Phase

• More cells die than divide due to toxic conditions.
• Some bacteria form endospores to survive harsh environments.

Quorum Sensing Importance

• It enables biofilm formation (Pseudomonas aeruginosa).
• It activates virulence genes (Vibrio cholerae causes cholera).
• It controls bioluminescence (Vibrio fischeri in squid).

Microbe of the Day: Pseudomonas aeruginosa

• Gram-negative, rod-shaped, opportunistic pathogen.
• Can survive in diverse environments like soil, water, and hospitals.
• Forms biofilms, which makes infections difficult to treat.
• It produces green-blue pigments (pyocyanin, pyoverdine).
• Causes infections in cystic fibrosis patients and burn victims.

Environmental Factors Affecting Microbial Growth

• Temperature determines enzyme function and membrane stability, such as Thermus aquaticus (Taq polymerase), which is heat-resistant.
• pH affects protein structure and metabolism, as seen in Helicobacter pylori, which is acid-tolerant and causes stomach ulcers.
• Oxygen determines metabolism type (aerobic vs. anaerobic), such as Clostridium botulinum, which is a strict anaerobe.
• Pressure: High pressure can denature proteins and affect membranes, such as in Barophiles in deep-sea vents.

Primary vs. Secondary Metabolism and Their Products

• Primary Metabolism supports growth and reproduction, producing DNA, RNA, proteins, and ATP that occur during the log (exponential) phase.
• Secondary Metabolism produces non-essential compounds that offer competitive advantages, such as antibiotics (penicillin, streptomycin), pigments, and toxins, which occur during the stationary phase.

Biofilms

• Biofilms are structured communities of bacteria embedded in a protective extracellular polymeric substance (EPS) and form on surfaces like teeth, medical implants, and water pipes.

Biofilm Formation Stages

• Attachment is where planktonic (free-swimming) bacteria attach to a surface.
• Microcolony Formation: Cells begin producing EPS (slime layer).
• Maturation: Complex structures form with channels for nutrient exchange.
• Dispersion: Some cells detach and colonize new areas.

Biofilm Importance

• Antibiotic Resistance: Biofilms protect bacteria, making them up to 1,000x more resistant to antibiotics.
• Disease Relevance: Biofilms contribute to infections like chronic wounds, catheter infections, and cystic fibrosis lung infections.
• Microbe Example: Pseudomonas aeruginosa forms antibiotic-resistant biofilms in hospital settings and can infect burn wounds and lungs (cystic fibrosis patients).

Microbial Metabolism: Energetics and Catabolism

• Microbes break down large molecules outside the cell using exoenzymes (e.g., proteases digest proteins).
• Small molecules are transported inside using passive transport (diffusion) or active transport (requires ATP).
• Redox reactions drive ATP production in cellular respiration: Oxidation is the loss of electrons (energy released), and reduction is the gain of electrons (energy stored).
• Glycolysis occurs in the cytoplasm
• Krebs Cycle (TCA Cycle) occurs in the cytoplasm
• Electron Transport Chain (ETC) occurs in the plasma membrane.
• Redox reactions drive ATP production in cellular respiration.

Types of Microbial Metabolism

• Photoautotrophs use light for energy and CO2 as a carbon source (e.g., Cyanobacteria).
• Chemoautotrophs use inorganic chemicals for energy and CO2 as a carbon source (e.g., Nitrosomonas).
• Photoheterotrophs use light for energy and organic compounds as a carbon source (e.g., Purple non-sulfur bacteria).
• Chemoheterotrophs use organic compounds for both energy and carbon (e.g., E. coli).
• Best electron donors yield the highest ATP.
• Glucose produces the most ATP and is used in aerobic respiration.
• Nitrate (NO3-) is used in anaerobic respiration.
• Less energy-efficient than nitrate, is Sulfate (SO42-).
• CO2 / Fermentation provides the least ATP when oxygen and other donors are unavailable.

Respiration and Electricity

• Some bacteria such as Geobacter use electron transport chains (ETC) to generate electricity (bioelectrogenesis) and can transfer electrons to metal surfaces, used in microbial fuel cells.

Fermentation Reactions

• No oxygen → No ETC → No oxidative phosphorylation; instead, NADH transfers electrons to pyruvate, producing waste products like lactic acid (in lactic acid bacteria) or ethanol (in yeast).

Bacterial Genetics: Transcription and Translation

• Differences between transcription and translation in Bacteria compared to Eukaryotes:
• Bacteria: Processes happen simultaneously (no nucleus).
• Eukaryotes: Processes are separate (transcription in the nucleus, translation in the cytoplasm).
• mRNA Processing Differences:
• Bacteria: No introns, no splicing.
• Eukaryotes: Introns removed, mRNA modified.
• Ribosome Differences:
• Bacteria: 70S (targeted by antibiotics).
• Eukaryotes: 80S.

Antibiotics Targeting Translation

• Tetracyclines block tRNA binding to the ribosome.
• Macrolides (e.g., erythromycin) inhibit ribosome movement along mRNA.
• Aminoglycosides cause misreading of mRNA, producing faulty proteins.

Bacterial Genetic Information Transfer

• Transformation: Bacteria uptake naked DNA from the environment (e.g., Streptococcus pneumoniae).
• Conjugation: Plasmid transfer via sex pilus (e.g., E. coli).
• Transduction: Bacteriophages (viruses) transfer DNA between bacteria (e.g., Salmonella).

CRISPR

• CRISPR-Cas acts as a bacterial immune system against viruses.
• Bacteria store viral DNA sequences to recognize and destroy future infections.
• CRISPR is used for gene editing in medicine and research, as biotechnology applications.