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Microbiology: Prokaryotes - Bacteria and Archaea

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  • What are Proteobacteria and their key characteristics?
    Proteobacteria are a large group of Gram-negative bacteria, chemoheterotrophic, named after the shape-shifting Greek god Proteus, and divided into five classes: alpha, beta, gamma, delta, and epsilon.
  • What distinguishes Alphaproteobacteria?
    Alphaproteobacteria grow in low nutrient levels, often have stalks or buds called prosthecae, and include genera like Pelagibacter, Azospirillum, and Rickettsia.
  • What is the ecological role of Pelagibacter?
    Pelagibacter is one of the most abundant ocean microorganisms, very small, thrives in low-nutrient environments, and plays a key role in the Earth's carbon cycle.
  • What diseases are caused by Rickettsia species?
    Rickettsia are obligate intracellular parasites causing spotted fevers such as epidemic typhus (R. prowazekii), endemic murine typhus (R. typhi), and Rocky Mountain spotted fever (R. rickettsii), transmitted by insect and tick bites.
  • How do Caulobacter and Hyphomicrobium reproduce?
    They reproduce by budding rather than binary fission and are found in low-nutrient aquatic environments, forming stalks and prosthecae.
  • What is the significance of Rhizobium and Bradyrhizobium?
    These bacteria fix nitrogen in the roots of leguminous plants and are commonly called rhizobia.
  • What is the role of Agrobacterium in plants?
    Agrobacterium is a plant pathogen causing crown gall by inserting a plasmid into plant cells, inducing tumor formation.
  • What diseases are caused by Bartonella and Brucella?
    Bartonella henselae causes cat-scratch disease; Brucella is an obligate mammalian parasite causing brucellosis and survives phagocytosis.
  • What are Nitrobacter and Nitrosomonas known for?
    They are chemoautotrophic bacteria that oxidize inorganic nitrogen compounds: Nitrosomonas converts NH4+ to NO2-, and Nitrobacter converts NO2- to NO3-.
  • What are key features of Betaproteobacteria?
    Betaproteobacteria include Acidithiobacillus (oxidizes sulfur), Spirillum (flagellated freshwater bacteria), Sphaerotilus (forms protective sheaths), Burkholderia, Bordetella, Neisseria, and Zoogloea.
  • What diseases are caused by Bordetella and Neisseria?
    Bordetella pertussis causes whooping cough; Neisseria gonorrhoeae causes gonorrhea, and N. meningitidis causes meningococcal meningitis.
  • What are the main groups within Gammaproteobacteria?
    Includes Thiotrichales (Beggiatoa), Pseudomonadales (Pseudomonas), Legionellales (Legionella, Coxiella), Vibrionales (Vibrio), Enterobacteriales (Escherichia, Salmonella, Shigella, Klebsiella, Yersinia), and Pasteurellales.
  • What is unique about Enterobacteriales?
    Enterobacteriales are facultative anaerobes with peritrichous flagella, inhabit intestinal tracts, ferment carbohydrates, and include many pathogens like E. coli and Salmonella.
  • What diseases are caused by Vibrio species?
    Vibrio cholerae causes cholera; V. parahaemolyticus causes gastroenteritis.
  • What are Deltaproteobacteria known for?
    Deltaproteobacteria include Bdellovibrio, which attacks other Gram-negative bacteria, and Desulfovibrionales, which use sulfur compounds instead of oxygen as electron acceptors.
  • What is the lifestyle of Myxococcales?
    Myxococcales move by gliding, leave slime trails, aggregate to form fruiting bodies, and produce resistant myxospores.
  • What are characteristics of Epsilonproteobacteria?
    They are helical or curved, microaerophilic bacteria including Campylobacter (causes foodborne illness) and Helicobacter (causes peptic ulcers and stomach cancer).
  • What distinguishes Cyanobacteria?
    Cyanobacteria perform oxygenic photosynthesis, often have heterocysts for nitrogen fixation, possess gas vesicles for buoyancy, and can be unicellular or filamentous.
  • How do Chlorobi and Chloroflexi differ from Cyanobacteria?
    Chlorobi and Chloroflexi perform anoxygenic photosynthesis using H2S or organic compounds, unlike Cyanobacteria which use water and produce oxygen.
  • What are key features of Chlamydiae?
    Chlamydiae lack peptidoglycan, grow intracellularly, form infectious elementary bodies, and include pathogens causing trachoma, urethritis, psittacosis, and mild pneumonia.
  • What is unique about Planctomycetes?
    Planctomycetes like Gemmata obscuriglobus have a membrane-bound nucleoid resembling a eukaryotic nucleus.
  • What are Bacteroidetes and Fusobacteria?
    Bacteroidetes are anaerobic bacteria found in the mouth and large intestine; Fusobacteria are anaerobic, found in the mouth, and cause dental abscesses.
  • What defines Spirochaetes?
    Spirochaetes are coiled bacteria that move via axial filaments; include Treponema (syphilis), Borrelia (relapsing fever, Lyme disease), and Leptospira (excreted in animal urine).
  • What are Deinococcus and Thermus notable for?
    Deinococcus radiodurans is highly radiation-resistant; Thermus aquaticus is a thermophile and source of Taq polymerase used in PCR.
  • What are the main groups of Gram-positive bacteria?
    Gram-positive bacteria include Firmicutes (low G + C), Tenericutes (low G + C, wall-less), and Actinobacteria (high G + C).
  • What are characteristics of Firmicutes?
    Firmicutes include Clostridiales (endospore-forming anaerobes), Bacillales (Bacillus and Staphylococcus), and Lactobacillales (Lactobacillus, Streptococcus, Enterococcus, Listeria).
  • What diseases are caused by Clostridium species?
    Clostridium species cause tetanus, botulism, gas gangrene, and antibiotic-associated diarrhea.
  • What is unique about Mycoplasma?
    Mycoplasma lack a cell wall, are pleomorphic, and M. pneumoniae causes mild pneumonia.
  • What are key features of Actinobacteria?
    Actinobacteria are high G + C Gram-positive bacteria, often pleomorphic with branching filaments, including Mycobacterium (tuberculosis, leprosy), Corynebacterium, Propionibacterium, Gardnerella, Frankia, Streptomyces, Actinomyces, and Nocardia.
  • Which bacterial group produces most commercial antibiotics?
    Streptomyces, a genus of Actinobacteria, produces most commercially important antibiotics.
  • What are the main types of Archaea and their habitats?
    Archaea include extremophiles: Halophiles (require >25% salt), Thermophiles (grow >80°C), and Methanogens (anaerobic methane producers).