IndietroMicrobiology: Bacterial Structure and Function
06:17
Termini in questo insieme (30)
Cocci (spherical), Rods or Bacilli (elongated), Vibrios (comma-shaped), Spirilla (rigid spirals), and Spirochetes (flexible spirals).
Arrangement depends on the plane of cell division and whether cells separate. Examples include Diplococci (pairs), Streptococci (chains), Staphylococci (clusters), Tetrads (groups of 4), and Sarcina (cubic packets of 8).
Bacteria range from about 0.3 μm (smallest like Mycoplasma) to very large cells like Epulopiscium fishelsoni (~600 μm by 80 μm). Average bacteria like E. coli are 1.1 to 1.5 μm wide and 2 to 6 μm long.
A high surface area-to-volume ratio increases efficiency of nutrient uptake and diffusion within the cell, enhancing metabolic activity.
The cell envelope includes the plasma membrane, cell wall, and sometimes an outer layer such as a capsule or slime layer.
A thin (7-8 nm) bilayer of amphipathic phospholipids with embedded proteins. It acts as a selectively permeable barrier controlling nutrient uptake, waste elimination, and environmental sensing.
Hopanoids are hydrophobic molecules similar to cholesterol that stabilize membrane fluidity and form microdomains for protein complexes.
Macronutrients are needed in large amounts (e.g., carbon, nitrogen). Micronutrients are trace elements (e.g., zinc, manganese). Growth factors are organic compounds like amino acids and vitamins that bacteria cannot synthesize.
Mechanisms include passive diffusion, facilitated diffusion, primary and secondary active transport, and group translocation. Endocytosis occurs only in eukaryotes.
Energy from ATP hydrolysis moves substances against concentration gradients via carrier proteins like ATP-binding cassette (ABC) transporters, important for vitamins, ions, and sugars uptake.
Bacteria secrete siderophores that bind insoluble ferric iron (Fe3+), forming complexes that are transported into the cell via specific receptors and ABC transporters.
An energy-dependent process where the transported molecule is chemically modified during uptake, e.g., the phosphoenolpyruvate:sugar phosphotransferase system (PTS) phosphorylates sugars as they enter.
Peptidoglycan is a rigid, mesh-like polymer of sugars (NAG and NAM) and amino acids forming the sacculus that maintains cell shape and protects against osmotic stress.
Gram-positive have thick peptidoglycan layers with teichoic acids and a single membrane (monoderm). Gram-negative have thin peptidoglycan, an outer membrane with lipopolysaccharides (LPS), and a periplasmic space (diderm).
LPS contributes to negative surface charge, stabilizes the outer membrane, acts as a permeability barrier, and its lipid A portion functions as an endotoxin causing septic shock.
The cell wall prevents lysis in hypotonic environments by resisting swelling and protects the cell when water moves in or out, maintaining structural integrity.
Lysozyme breaks glycosidic bonds in peptidoglycan; penicillin inhibits its synthesis. Both cause cell lysis in hypotonic environments due to loss of cell wall integrity.
Small membrane-bound particles released from membranes; they transfer genetic material, toxins, and interact with other cells, aiding in communication and pathogenesis.
Capsules are well-organized polysaccharide layers protecting against phagocytosis. Slime layers are diffuse and easily removed. S-layers are protein arrays protecting from environmental stress and aiding adhesion.
Protein filaments homologous to eukaryotic actin and tubulin that maintain cell shape, localize proteins, and participate in cell division.
Inclusions are aggregates of stored substances (organic/inorganic). Microcompartments are protein shells enclosing enzymes, e.g., carboxysomes for CO2 fixation.
The nucleoid contains the single circular chromosome compacted by supercoiling. Plasmids are small, extrachromosomal DNA molecules that replicate independently and can carry advantageous genes.
Pili are short protein appendages for attachment and DNA transfer. Flagella are long, whip-like structures for motility with distinct arrangements like monotrichous or peritrichous.
Flagella rotate like propellers; counterclockwise rotation causes forward runs, clockwise causes tumbling to reorient. Energy comes from proton motive force or ATP.
Movement toward chemical attractants or away from repellents by altering run and tumble frequency based on chemical gradients detected by chemoreceptors.
Dormant, highly resistant structures formed by some bacteria (e.g., Bacillus, Clostridium) to survive harsh conditions. Important in food safety and disease due to their resistance and longevity.
Consists of a core with DNA and ribosomes, surrounded by a cortex of thick peptidoglycan, a protein spore coat, and sometimes an exosporium outer layer.
DNA replication, asymmetric cell division forming forespore and mother cell, engulfment, cortex and coat formation, dehydration, and mother cell lysis releasing mature endospore.
Low water content, high calcium-dipicolinic acid, protective spore coat, impermeable inner membrane, DNA-binding proteins, and low pH stabilize and protect the spore.
Activation prepares spores, germination involves rehydration and cortex breakdown triggered by germinant receptors, and outgrowth is emergence of a vegetative cell.