Methods Used by Bacteria for Nutrient Uptake


Passive Diffusion

  • Molecules move from an area of high concentration to an area of lower concentration
  • Only very small molecules like H2O and CO2 - non-polar only
  • Does not involve carrier proteins
  • Moves along the concentration gradient
  • ATP not required
  • Reversible movement
  • Shows saturation
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Facilitated Diffusion

  • Diffusing involving carrier proteins (permeases)
  • Rate of diffusion increases with the concentration gradient
  • Major intrinsic proteins (MIPs) facilitate diffusion
  • Small, polar molecules eg. glycerol
  • ATP not required
  • Shows saturation
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Active Transport

  • Transport of solute molecules to a higher concentration
  • ATP is needed
  • Involves use of permeases
  • Against the concentration gradient
  • Shows saturation
  • Irreversible
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Group Translocation

  • Molecule is chemically modified as it is brought into the cell
  • Type of active transport
  • Well known example is the PTS system - in this system when a sugar is taken up it gets phosphorylated using PEP as the phosphate donor, yielding pyrivate
  • Most aerobes except Bascillus lack a PTS system
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Iron Uptake - Gram Negative Bacteria

  • Numerous pathways, unlcuding uptake from transferrin, siderophores or heme
  • All require an outer membrane receptor, a Periplasmic Binding Protein or an inner membrane ATP Binding Cassetle
  • Not all bacteria have all 3, but some have more than 1 type
  • Outer membrane receptor (very specific) to get through to periplasm ---> once in need PBP ---> need an ATP transporter to get through to cytoplasm
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Iron Uptake - Gram Positive Bacteria

  • Uptake of iron from heme, siderophore or transferrin
  • Involves membrane Anchored Binding Protein and a membrane associated ATP Binding Cassetle
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