Microbiology - Prokaryotes

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Prokaryote

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Single-celled organism lacking nuclei and membrane-bound organelles.

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Prokaryotic Cell Components

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DNA/RNA, Plasma Membrane, Cytoplasma/Cytoskeleton, and Ribosomes.

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Ways to Classify Prokaryotes

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Shapes, Staining, Metabolism & Physiology, Habitat, Genetics

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Shapes

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Cocci, Bacilli, and Spiralla

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Cocci

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Spherical; single, diplococci (two), tetrad (four), sarcinae (multiples of eight), chain, or irregular cluster.

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Bacilli

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Rods; single, diplobacilli (two), streptobacilli (chain), coccobacilli (intermediate), palisades (Jacob's ladder).

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Spiralla

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Spiral-shaped; almost always single; vibrios (no true rotation), spirilla (at least 1 helical turn, flagella at polar ends), spirochete (at least 3 helical turns, periplasmic flagella).

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Gram Staining

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Determined by structure forming outermost layer.

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Gram Positive

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Thick peptidoglycan (stain)

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Gram Negative

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Outer membrane blocks thin peptidoglycan (no stain)

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Metabolism Classification

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Inorganic carbon source (autotroph), organic carbon source (heterotroph), chemical source (chemotroph), light source (phototroph), oxygen source (obligate aerobe), oxygen-poor environment (obligate anaerobes), either oxygen rich or poor environments (facultative anaerobes).

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Habitat Classification

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Acidophile (acid), halophile (salt), thermophile (heat), extremophile (extreme environments).

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Genetic Classification

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Based on phylogenetics; allows for intelligent drug design.

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Medical Classification

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Clinicians use phenotypic characteristics for practicality: Bergey's Manual.

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Division I

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Gracilicutes (Gram -)

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Division II

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Firmicutes (Gram +)

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Division III

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Tenericutes (no cell wall)

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Division IV

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Archaebacteria

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Appendages

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External structures responsible for locomotion or attachment.

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Flagellum

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Whip-like appendage for motility composed of a filament (provides mvmt), hook (insertion site), and basal apparatus (anchor).

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Flagella in Bacteria

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Most spirochetes, half of bacilli, few of cocci.

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Flagellar Arrangement

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Polar ends - monotrichus at one end, lophotrichus multiple flagella from one point, and amphitrichus at both ends. Random (peritrichous). Periplasmic - internal, wrapped around bacterial body.

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Types of Movement

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Chemotaxis (in response to mvmt - pos. toward / neg. away from), phototaxis (in response to light).

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Fimbriae

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Small, bristle-like appendage for attachment; allow bacteria cells to colonize.

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Pili

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Appendage used for reproduction seen in gram - bacteria.

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Conjugation

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Bacteria "sex."

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Glycocalyx

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Extra outer layer composed of macromolecules used to prevent dessication, protect from immune system (ex. capsules), and to encourage colonization.

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Biofilms

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Accumulation of microorganisms in thick layers due to fimbriae and glycocalyces. Medical implications such as artificial joints and catheter colonies).

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Quorum Sensing

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Ability of bacterial colony to sense its population density and coordinate activities.

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Cell Envelope

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External membrane complex. Cell wall, cell membrane (and outer membrane in gram - bacteria).

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Cell Membrane

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Composed of phospholipids and proteins, directs molecular transport, secretion, and metabolism. Innermost structure.

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Cell Wall

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Composed mainly of peptidoglycan, maintains shape and integrity: tenericutes have none, firmicutes (Gram +) thick, gracilicutes (Gram -) thin.

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Cell Wall Layers

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Cytoplasm, Cell Membrane, Peptidoglycan, Outer Membrane, and Glycocalyx (sometimes).

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Periplasmic Space

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Gram + between peptidoglycan and cell membrane / Gram - also between peptidoglycan and outer membrane.

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Peptidoglycan

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N-acetyl glucosamine (NAG) and N-acetyl muramic acid (NAM) polysaccharides cross-linked together.

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Peptidoglycan Variation

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Firmicutes: thick with acidic polysaccharides (LTA and TA), gives wall flexibility. Gracilicutes: thin with greater flexibility, but greater susceptability to lysis.

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Outer Membrane

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Only in Gracilicutes: outer layer LPS lipid endotoxin and receptors / inner layer phospholipids with lipoproteins. Regulated by porins.

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Cytoplasm

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95% water + amino acids, salts, sugars.

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Nucleoid

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Genetic material packaged in a single circle of DNA, sometimes with extra chromosomes.

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Plasmids

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Double-stranded accessory DNA found in every bacterium with an indefinite amt. Can carry drug resistance genes, extra enzymes, or toxins. Often swapped between species.

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Ribosomes

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Protein-making machinery 60% rRNA and 40% protein.

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Polysomes

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Strings of ribosomes.

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Inclusion Bodies

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Intracellular nutrient stores built during times of abundance and consumed during scarcity. Composed of glycogen and poly-beta-hydroxybutyrate.

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Cytoskeleton

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Made principally of actin, holds shape; common in bacilli and spirilla, less so in cocci.

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Sporulation

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Spore formation induces dormant state when nutrients are scarce, or in the the wrong environmental conditions.

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Endospore

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Bacterial spore.

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Vegetative Cell

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Metabolically active in the right environment.