Topic 5
What is the coevolution hypothesis?
Viruses originated around the same time as other microbes and have been coevolving with them.
What are aerotolerant anaerobes?
Organisms that do not use oxygen for growth but can survive and grow in its presence.
What are the two main types of sporulating gram-positive bacteria?
- Bacillus
- Clostridium
What is the difference between homofermenters and heterofermenters?
Homofermenters: metabolize glucose exclusively into lactic acid.
Heterofermenters: metabolize glucose into multiple end-products (lactic acid, carbon dioxide, ethanol...)
What are 4 ways to quantify viruses?
- Direct count
- Hemagglutination
- Plaque assay
- Endpoint assay
Describe the general structure of a virus.
What is anabolism and catabolism?
Anabolism: the building of complex molecules from simpler ones, requiring energy.
Catabolism: the breakdown of complex molecules into simpler ones, releasing energy that can be used by the cell.
Fill in these blanks about nitrifiers:
- Nitrosococcus + Nitrosomonas are ______ oxidizers.
- Nitrobacter + Nitrospira are _______ oxidizers.
- Ammonia
- Nitrite
What is the minimum, maximum and optimal temperature for Psychrophiles?
Minimum: 0 degrees
Maximum: 20 degrees
Optimal: 15 degrees
What is an autoclave, and under what conditions does it operate for sterilization?
An autoclave is a device used for sterilizing equipment and materials through the use of steam under pressure.
It operates at a temperature of 121°C and a pressure of 15 psi.
Compare the lytic cycle and the lysogenic cycle.
Lytic cycle: viruses enter, replicate, and lyse host cells.
Lysogenic cycle:
Phage integrates its genome with the host, becoming a prophage
This genome is replicated until the host starts to stress (host becomes a lysogen)
The phage then lyses the cell
What is pasteurization?
A process that uses heat to kill harmful microorganisms in food and drinks without affecting their flavour and quality.
What are Firmicutes?
A division of gram-positive bacteria that are known to have low guanine-cytosine (GC) content in their DNA.
Non-sporulating Firmicutes, like Staphylococcus, are often found on animals, including human skin.
A microorganism gains energy from the oxidation of hydrogen sulfide (H₂S) and uses CO₂ as its carbon source.
Classify the microorganism above based on its nutrition sources as either photosynthetic or chemosynthetic for energy, organotrophic or lithotrophic for electron source, and heterotrophic or autotrophic for carbon source.
What are 3 ways for a virus to enter an animal cell? Explain at least 1 of them in detail.
Endocytosis: The virus attaches to a receptor on the host cell surface, and the cell engulfs the virus in a vesicle, internalizing it into the cytoplasm.
Membrane fusion: Enveloped viruses can fuse their lipid bilayer with the host cell membrane, releasing the viral genome directly into the cell's cytoplasm.
Endocytosis of an enveloped virus: the virus is engulfed into the cell by endocytosis, and the viral envelope fuses with the endosomal membrane, allowing the viral genome to be released into the host cell.
What are the steps of viral replication?
1. Adhere: stick to a host cell
2. Enter the cell
3. Uncoat: release viral genome
4. Synthesis: express and replicate genome
5. Assembly: create new virus particles
6. Exit: new particles leave host cell
Define selective, differential, and enriched media.
Selective media: contains chemicals that inhibit the growth of certain organisms while allowing the growth of the desired organism (allows isolation).
Differential media: allows certain microbes to be recognized based on visual reactions in the medium.
Enriched media: enriched with nutrients to increase a population of microbes with a specific property.
What are the characteristics of enterics?
(Bonus: what are coliforms?)
Compare depth filters, conventional membrane filters, and nucleopore filters - Which one is used for sterilization?
Depth Filters are fibrous sheets that remove suspended particles but have larger pore sizes, so bacteria and viruses can still get through.
Conventional Membrane Filters are polymer filters that have very small pores (0.22 micrometers), which remove bacteria and larger microorganisms, thus effective for sterilization.
Nucleopore Filters are thin polycarbonate films that are too fragile for routine sterilization, more useful for microscopy.
Explain what viroids and prions are, and describe their methods of replication.
Viroids are small, circular RNA molecules that can self-replicate and interfere with host cell processes, typically in plants. Unlike viruses, they lack a protein coat (capsid) and cannot encode any genes to produce proteins.
Prions are proteinaceous infectious particles. They do not replicate in the traditional sense, but propagate by causing normal proteins to misfold, which can lead to neurodegenerative diseases such as mad cow disease.
Define hemagglutination, and compare a shield well and a button well: which one indicates a higher concentration of viruses?
A shield well appears as a smooth, uniform layer of cells covering the bottom of the well, indicating a positive result where hemagglutination has occurred = more viruses.
A button well shows a small, compact pellet of cells at the bottom, meaning no hemagglutination has occurred = not many viruses.
Name 3 classes of common disinfectants/antiseptics and briefly describe their mechanism and when they're used.
- Alcohol: alcohol-based disinfectant that works by disrupting cell membranes. Commonly used for hand sanitizers and cleaning surfaces in lab settings (ex. Ethanol).
- Phenolics: also disrupt cell membrane, often used in soaps, deodorants, and cosmetics (ex. Triclosan).
- Oxidizing agents: kills microorganisms by oxidizing cell components. Commonly added to swimming pools and hot tubs to inhibit microbial growth (ex. Sodium Hypochlorite).
What are fruiting bodies and multicellular pigmented bodies in Gliding Myxobacteria?
Fruiting Bodies: multicellular aggregates of gliding myxobacteria formed when there's not enough nutrients. They contain myxospores, which are highly resistant spores that help the bacteria survive in harsh environments.
- Fruiting bodies are often visible to the naked eye, especially in environments like decaying wood or dung pellets.
Pigmented Bodies: multicellular structures that form during times of nutrient scarcity, similar to fruiting bodies, but they are pigmented due to the production of antioxidants. They protect the cells within the aggregate from oxidative stress.
Explain what the Endpoint Assay is in virus quantification, and define TCID50 and LD50.
The Endpoint Assay is a method used to determine the concentration of viruses in a sample by measuring the dilution at which 50% of cells or test subjects exhibit a specific response.
TCID₅₀ (Tissue Culture Infectious Dose 50%): the amount of virus needed to induce a cytopathic effect (CPE), which is damage or visible change in cultured cells, in 50% of the cell cultures.
LD₅₀ (Lethal Dose 50%): This is the amount of virus required to kill 50% of test animal subjects.
Name one broad-spectrum antibiotic and one narrow-spectrum antibiotic.
Broad: Tetracycline
Narrow: Polymyxin B, penicillin, streptomycin...