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Microbiology: Prokaryotic Organisms and Classification

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  • What are the main shapes of prokaryotic cells?

    Coccus (spherical), Bacillus (rod-shaped), Spirals (spirilla and spirochetes), Vibrio (curved rods), Coccobacillus (intermediate), and Pleomorphic (variable shapes).

  • What are endospores and their significance?

    Endospores are dormant, highly resistant structures formed by some Gram-positive bacteria like Bacillus and Clostridium. They protect against harsh conditions and are not reproductive but defensive.

  • Describe binary fission in prokaryotes.

    Binary fission is the most common asexual reproduction method where the cell duplicates DNA, elongates, forms a cross wall, and divides into two identical daughter cells.

  • What is snapping division in prokaryotic reproduction?

    Snapping division is a variation of binary fission where only the inner cell wall forms, causing the outer wall to snap and partially separate daughter cells.

  • Explain budding as a prokaryotic reproductive method.

    Budding involves a new cell developing from a bud on the parent cell, which eventually detaches as a separate organism.

  • What is viviparity in prokaryotes?

    Viviparity is a unique reproduction where live offspring emerge from the dead mother cell, observed in Epulopiscium.

  • How do prokaryotic cell arrangements form?

    Arrangements depend on the division planes and whether daughter cells remain attached, e.g., diplococci, streptococci, tetrads, sarcinae, and staphylococci for cocci.

  • What are the three domains of life in modern prokaryotic classification?

    Archaea, Bacteria, and Eukarya, based on genetic relatedness.

  • List key features of Archaea.

    Archaea lack peptidoglycan in cell walls, have branched hydrocarbon membrane lipids, use AUG codon for methionine, reproduce asexually, and do not cause known diseases.

  • What are extremophiles and examples?

    Extremophiles are archaea thriving in extreme conditions: thermophiles (>45°C), hyperthermophiles (>80°C), and halophiles (high salt). Examples: Thermococcus, Halobacterium salinarum.

  • What role do methanogens play?

    Methanogens are obligate anaerobes producing methane from CO2, hydrogen, and organic acids, important in sediment waste conversion and environmental methane production.

  • What are cyanobacteria and their significance?

    Cyanobacteria are Gram-negative phototrophs using chlorophyll a to produce oxygen, believed to oxygenate early Earth’s atmosphere; some fix nitrogen in heterocysts.

  • How is G + C content used in bacterial classification?

    The percentage of guanine-cytosine base pairs classifies Gram-positive bacteria into low G + C (<50%) and high G + C groups.

  • Name some low G + C Gram-positive bacteria and their traits.

    Includes Clostridia (anaerobic, spore-forming), Mycoplasmas (no cell wall), Bacillus (soil, spore-forming), Listeria (foodborne), Lactobacillus (beneficial), Streptococcus, and Staphylococcus (human pathogens).

  • What are characteristics of high G + C Gram-positive bacteria?

    Phylum Actinobacteria includes Corynebacterium (diphtheria), Mycobacterium (tuberculosis, leprosy), and Actinomycetes (filamentous, antibiotic producers).

  • What defines Proteobacteria and its classes?

    Proteobacteria are diverse Gram-negative bacteria divided into Alpha-, Beta-, Gamma-, Delta-, Epsilon-, and Zetaproteobacteria based on rRNA sequences.

  • Key features of Alphaproteobacteria?

    Typically aerobes, grow at low nutrients, some have prosthecae; includes nitrogen fixers like Rhizobium, pathogens like Rickettsia and Brucella.

  • Important Betaproteobacteria genera and roles?

    Includes Nitrosomonas (nitrification), Neisseria (gonorrhea), Bordetella (whooping cough), and Burkholderia (lung infections).

  • What are notable Gammaproteobacteria?

    Largest class with diverse metabolism; includes pathogens like Legionella, Coxiella, Pseudomonas, and Enterobacteriaceae family with Escherichia coli.

  • Describe Deltaproteobacteria and Epsilonproteobacteria.

    Deltaproteobacteria include sulfur reducers and bacterial predators; Epsilonproteobacteria include pathogens like Campylobacter and Helicobacter.

  • What are Chlamydias and their medical importance?

    Chlamydias are Gram-negative cocci causing neonatal blindness, pneumonia, and the most common bacterial STD in the US.

  • Characteristics of spirochetes?

    Spirochetes are flexible, motile, helical bacteria including Treponema (syphilis) and Borrelia (Lyme disease).

  • What are Bacteroids and their roles?

    Bacteroides are obligate anaerobes in the digestive tract; Cytophaga degrades wood and sewage.