Prokaryotes: Vocabulary Flashcards

Prokaryotes: Overview, Habitats, and Diversity

  • Prokaryotes are the most diverse group of cellular microbes.
  • Habitats range from extreme to ordinary:
    • Antarctic glaciers
    • Thermal hot springs
    • Colons of animals
    • Cytoplasm of other prokaryotes
    • Distilled water
    • Supersaturated brine
    • Disinfectant solutions
    • Basalt rocks
  • Only a few prokaryotes routinely colonize humans or cause disease.
  • Bacterial shapes are illustrated in Figure 11.1 (typical morphologies).

Prokaryotes: Reproduction

  • All prokaryotes reproduce asexually.
  • Main methods of asexual reproduction:
    • Binary fission (most common)
    • Snapping division (G+ bacilli)
    • Spore formation (Actinomycetes)
    • Fragmentation (Cyanobacteria)
    • Budding (Hyphomicrobium)
    • Viviparity (Epulopiscium)
  • Visual references: Binary fission (Figure 11.2), Snapping division (Figure 11.3), Actinomycetes spores (Figure 11.4).

Prokaryotes: Cell Arrangement

  • Arrangements arise from two aspects of binary fission:
    • Planes in which cells divide
    • Separation of daughter cells
  • Figure 11.6 highlights arrangements of cocci; Figure 11.7 highlights arrangements of bacilli.

Endospores

  • Endospores are a defensive strategy against unfavorable conditions.
  • Endospores are a major concern for food processors, healthcare professionals, and governments due to their resilience.
  • Location and structure are summarized in Figure 11.8 (Locations of endospores).

Archaea: General Characteristics

  • Gram reaction varies among Archaea.
  • Cell membrane lipids have branched hydrocarbon chains.
  • No peptidoglycan in the cell wall.
  • Habitats include anaerobic sediments and extreme environments.
  • Important genera include: Geogemma, Pyrodictium, Methanobacterium, Halobacterium, Sulfolobus.
  • Representative archaeal groups and traits:
    • Thermophiles: DNA/RNA/cytoplasmic membranes, and proteins do not function properly below 45∘C45^{\circ}\mathrm{C} (thermophiles function above this temperature).
    • Hyperthermophiles: require temperatures over 80∘C80^{\circ}\mathrm{C}.
    • Represented genera: Geogemma, Pyrodictium.
  • Halophiles: inhabit extremely saline habitats; require greater than 9%9\% NaCl to maintain cell wall integrity; many have red or orange pigments that help protect from light; example: Halobacterium salinarium.
  • Methanogens: convert carbon dioxide, hydrogen gas, and organic acids to methane; contribute methane in pond, lake, and ocean sediments; some live in animal colons; estimated methane production on the ocean floor is about 1013 tons10^{13}\text{ tons} (i.e., ~10 trillion tons).
  • Deeply Branching Bacteria: thought to be among the earliest bacteria; autotrophic; habitats resemble early Earth; includes Deinococcus.
  • Oxygenic photosynthetic cyanobacteria (blue-green): gram-negative; produce oxygen via photosynthesis; many fix nitrogen using heterocysts; exhibit gliding motility; habitat includes aquatic environments (e.g., sludge at bottom); important genera include Cyanobacterium.
  • Figure 11.13 provides a cyanobacteria overview.
  • Orange archaea ( Yellowstone image, Figure 11.11) illustrate halophilic/thermophilic archaeal life in extreme environments.

Mycoplasmas

  • No cell wall; pleomorphic cell shapes.
  • Facultative or obligate anaerobes.
  • Among the smallest free-living cells.
  • Often parasites of animals, plants, and insects.
  • Generally susceptible to macrolides and quinolones.
  • Some pathogens include Mycoplasma vaginalis.

Gram-Positive Cocci

  • Habitat: soils, skin and mucous membranes of animals.
  • Important genera: Staphylococcus, Streptococcus, Lactococcus, Enterococcus.
  • Notable species:
    • Staphylococcus epidermidis
    • Staphylococcus aureus (facultative anaerobe; yellow-pigmented colonies; causes folliculitis, carbuncle, impetigo, scalded skin syndrome)
    • Streptococcus pyogenes (Group A strep; extracellular substances; necrotizing fasciitis)
    • Streptococcus pneumoniae
    • Streptococcus mutans
    • Lactococcus lactis
    • Enterococcus faecalis
  • Visual references: Staphylococcus aureus, Staphylococcus epidermidis; Streptococcus spp.; Lactococcus lactis.

Gram-Positive Endospore-Forming Rods

  • Important pathogens and industrial organisms.
  • Habitat: soils and animal intestinal tract.
  • Important genera:
    • Clostridium (obligate anaerobe)
    • Bacillus (aerobic or facultative)
  • Notable species: Clostridium botulinum, Clostridium tetani, Clostridium perfringens, Clostridium difficile; Bacillus thuringiensis; Bacillus anthracis; Bacillus cereus.
  • Figures referenced: 11.15 (Clostridium botulinum, C. tetani, C. perfringens, C. difficile); 11.16 (Gram+ regular rods including Bacillus spp.).

Gram-Positive Regular Rods

  • Habitat: dairy products, genital and oral cavities, animal feces; soils.
  • Important genera: Lactobacillus, Listeria monocytogenes (food contamination).
  • Examples: Lactobacillus acidophilus; Listeria monocytogenes.
  • Context: industrial and clinical relevance includes fermentation and foodborne illness.

Gram-Positive Irregular Rods

  • Habitat: soil; include human pathogens.
  • Important genera:
    • Epulopiscium fishelsoni
    • Corynebacterium diphtheriae
    • Propionibacterium acnes
    • Streptomyces griseus
    • Actinomyces
    • Nocardia asteroides
  • Notable traits:
    • Epulopiscium fishelsoni (unusually large)
    • Actinomyces: branching filaments with reproductive conidiospores
    • Nocardia: aerobic; some are acid-fast; form branched filaments and fragmentation
  • Visuals: Corynebacterium diphtheriae, Epulopiscium fishelsoni, Streptomyces griseus, Actinomyces, Nocardia asteroides; Gram+ acid-fast staining context.

Gram-Positive Acid-Fast Staining Bacteria

  • Aerobic rods that form filaments.
  • Habitat: soil, plants, animals.
  • Important genus: Mycobacterium (e.g., M. ulcerans, M. tuberculosis, M. leprae, M. smegmatis).

Gram-Negative: Aerobic Rods

  • Groups:
    • Bdellovibrio
    • Spirillum
    • Campylobacter jejuni (one polar flagellum; gastroenteritis)
    • Azospirillum (associated with plant roots; nitrogen fixer)
    • Rhizobium (nitrogen fixer; forms nodules on legume roots; e.g., pea roots)
  • Representative genera listed in Pearson, 2010 (Figure 11.19 overview).
  • Additional genera often discussed:
    • Pseudomonas aeruginosa
    • Legionella pneumophila
    • Francisella tularensis
    • Burkholderia
    • Bordetella pertussis
    • Brucella abortus
    • Agrobacterium
  • Rhizobium note: nodulation on legumes; nitrogen fixation is agriculturally important.

Gram-Negative: Aerobic Rods (continued) – notable pathogens

  • Burkholderia: nosocomial infections; polar flagella; can grow in disinfectant solutions.
  • Bordetella pertussis: coccobacillus/rod; airborne; non-motile.
  • Brucella abortus: nonmotile cocobacilli; survive phagocytosis.
  • Agrobacterium: plant pathogen with genetic relevance to plant transformation.
  • Neisseria species (Gram-negative facultative anaerobic cocci):
    • Neisseria meningitidis: chemoheterotrophic; human nasopharynx; capsule.
    • Neisseria gonorrhoeae: chemoheterotrophic; human genital tract.

Gram-Negative: Facultative Anaerobic Rods

  • Many important pathogens.
  • Fine-tuned adherence via fimbriae; some produce bacteriocins that lyse competitor cells.
  • Habitats: soil, plants, respiratory and intestinal tracts.
  • Important genera include: Escherichia, Klebsiella, Salmonella, Proteus, Shigella, Yersinia, Serratia, Vibrio, Haemophilus, Pasteurella, Enterobacter, Gardnerella.
  • Escherichia coli:
    • Ferments lactose; most strains non-pathogenic
    • Prevalent intestinal bacterium; notable pathogenic toxin-producing strain O157:H7.
  • Klebsiella pneumoniae:
    • Lactose fermenter; normal flora in mouth, skin, and intestines
    • Nosocomial infections; UTIs; opportunistic necrotizing pneumonia.
  • Salmonella:
    • Peritrichous flagella
    • Transmission via fecal-oral route; contaminated food/water; reduced stomach acid
    • Causes typhoid fever and salmonellosis; S. typhi mentioned specifically.
  • Proteus vulgaris and Proteus mirabilis:
    • Found in soil, water, and human colon
    • Nosocomial infections; UTIs, wound infections, bacteremia, and sepsis
    • Treatment often includes cephalosporins or fluoroquinolones.
  • Shigella flexneri:
    • Shigellosis in humans; fecal-oral spread.
  • Yersinia pestis:
    • Bubonic plague; transmitted by fleas and droplets.
  • Serratia marcescens: listed among Gram-negative facultative rods.
  • Pasteurella multocida:
    • Non-motile animal pathogen; sepsis in cattle; fowl cholera in chickens; pneumonia in other hosts.
  • Vibrio cholerae:
    • Found in coastal waters; associated with shellfish and plankton; transmitted via contaminated water or raw/undercooked seafood; fecal-oral spread.
  • Vibrio parahaemolyticus: another Vibrio species of note.
  • Haemophilus influenzae:
    • Contains capsule; resides in upper respiratory and intestinal tracts, mouth, vagina; requires blood in the medium for growth.
  • Haemophilus ducreyi.
  • Enterobacter aerogenes:
    • Causes UTI; nosocomial infections.
  • Gardnerella vaginosis (listed under Gram-negative facultative rods).

Gram-Negative: Obligate Anaerobic Rods

  • Habitats: mostly in intestinal tracts; some in mouth and genital tract.
  • Common representatives in the intestine include Fusobacterium and Bacteroides.

Gram-Negative: Obligate Intracellular Parasites

  • Parasites of arthropods and animals; important pathogens.
  • Important genera: Rickettsia, Coxiella, Ehrlichia, Chlamydia.
  • Rickettsia species:
    • R. prowazekii — epidemic typhus; transmitted by lice
    • R. typhi — endemic murine typhus; transmitted by rat fleas
    • R. rickettsii — Rocky Mountain spotted fever
  • Chlamydophila spp.: C. pneumoniae, C. psittaci
  • Chlamydia trachomatis

Spirochetes

  • Gram-negative; morphology is helical (corkscrew-shaped).
  • Motility via axial filaments.
  • Habitats: aquatic and animal parasites.
  • Important genera:
    • Leptospira
    • Treponema pallidum
    • Borrelia burgdorferi
  • Leptospira: excreted in urine; immunizations available.
  • Treponema pallidum: causative agent of syphilis (contextual reference).
  • Borrelia burgdorferi: causative agent of Lyme disease; transmitted by deer ticks.

Connections to Foundations, Applications, and Implications

  • Ecological and evolutionary relevance:
    • Archaea showcase adaptations to extreme environments (thermophiles, halophiles, methanogens) reflecting early Earth conditions.
    • Deeply branching bacteria provide clues about early autotrophic life and nutrient cycling.
  • Medical and public health relevance:
    • Endospore-forming bacteria (Clostridium, Bacillus) pose risks in food safety, clinical settings, and bioterror considerations; resilience requires robust sterilization.
    • Nosocomial infections involve several Gram-negative and Gram-positive taxa (e.g., Burkholderia, Klebsiella, Enterobacter, Pseudomonas, Staphylococcus, Enterococcus), guiding infection control practices.
    • Chlamydia, Rickettsia, and other intracellular pathogens require host interaction understanding and specialized diagnostic approaches.
  • Agricultural relevance:
    • Rhizobium and Azospirillum fix nitrogen in association with plant roots, boosting soil fertility and crop yields; nodulation shown on pea roots (Figure 11.19).
  • Food microbiology and industrial applications:
    • Lactobacillus and other Gram-positive rods are important in fermentation and food safety.
    • Lactobacillus acidophilus as a probiotic example; Listeria monocytogenes as a notable foodborne pathogen.
  • Evolutionary and practical implications of cyanobacteria:
    • Oxygenic photosynthesis by cyanobacteria transformed Earth's atmosphere; heterocysts enable nitrogen fixation under photosynthetic conditions; cyanobacterial Blooms and ecological roles in aquatic systems.

Summary of Key Terminology and Concepts

  • Endospore: dormant, tough, and non-reproductive structure enabling survival under harsh conditions.
  • Heterocysts: specialized cells in some cyanobacteria that fix nitrogen.
  • Nitrogen fixation: conversion of N2 to bioavailable forms (ammonia/nitrate).
  • Obligate vs. facultative: dependence on an environment (obligate anaerobe vs. facultative anaerobe).
  • Acid-fast staining: diagnostic staining method for certain genera (e.g., Mycobacterium) due to lipid-rich cell walls.
  • Nosocomial infections: infections acquired in healthcare settings.
  • Peritrichous flagella: many flagella distributed around the cell surface (common in Enterobacterales).
  • Polar flagella: flagellum(s) located at one or both ends of the cell (e.g., Campylobacter jejuni).

Notable Numerical References and Formulas

  • Temperature thresholds for Archaea:
    • Thermophiles: function issues below 45∘C45^{\circ}\mathrm{C}
    • Hyperthermophiles: require temperatures over 80∘C80^{\circ}\mathrm{C}
  • Salinity requirement for halophiles: greater than 9%9\% NaCl
  • Methane production by methanogens: approximately 1013 tons10^{13}\text{ tons} of methane buried on the ocean floor
  • Notable temperature and salinity constraints are central to understanding archaeal ecology and metabolism.

Figures Referenced (for context)

  • Figure 11.1: Typical prokaryotic morphologies
  • Figure 11.2: Binary fission
  • Figure 11.3: Snapping division
  • Figure 11.4: Actinomycetes spores
  • Figure 11.5: Budding
  • Figure 11.6: Arrangements of cocci
  • Figure 11.7: Arrangements of bacilli
  • Figure 11.8: Locations of endospores
  • Figure 11.11: Orange archaea in Yellowstone
  • Figure 11.13: Cyanobacteria overview
  • Figure 11.15: Clostridium botulinum and related species
  • Figure 11.16: Gram-positive regular rods
  • Figure 11.19: Nodules on pea roots (Rhizobium)

Quick reference taxonomy by major groups (highlights)

  • Archaea: Thermophiles, Hyperthermophiles, Halophiles, Methanogens
  • Deeply Branching Bacteria: Autotrophic, early Earth analogs, Deinococcus
  • Cyanobacteria: Oxygenic photosynthesis, nitrogen fixation, gliding motility
  • Mycoplasmas: No cell wall, smallest free-living cells
  • Gram-Positive cocci: Staphylococcus, Streptococcus, Lactococcus, Enterococcus
  • Gram-Positive rods: Clostridium, Bacillus, Lactobacillus, Listeria
  • Gram-Negative Aerobic Rods: Pseudomonas, Legionella, Campylobacter, Rhizobium, Azospirillum, Burkholderia, Bordetella, Brucella, Agrobacterium
  • Gram-Negative Facultative Cocci: Neisseria
  • Gram-Negative Facultative Rods: Escherichia, Klebsiella, Salmonella, Proteus, Shigella, Yersinia, Serratia, Vibrio, Haemophilus, Pasteurella, Enterobacter, Gardnerella
  • Gram-Negative Obligate Anaerobes: Fusobacterium, Bacteroides
  • Gram-Negative Obligate Intracellular Parasites: Rickettsia, Coxiella, Ehrlichia, Chlamydia
  • Spirochetes: Leptospira, Treponema pallidum, Borrelia burgdorferi
  • Key pathogens and concepts (e.g., Y. pestis, V. cholerae, M. tuberculosis, C. diphtheriae) reflect clinical relevance and diagnostic challenges.