Where do cells live?
In water
- oceans, rivers, lakes
- soils, sediments rocks –> wet pore spaces
- in multicellular organisms –> in aqueous conditions
Why do cells need to live in aqueous conditions?
- take up nutrients from the water
- release waste, ligands etc into water
cells need to be hydrophilic to allow chemical exchange with water
organic substrates (inc cells) are largely hydrophobic - sometimes hydrophobic is better - to take up organic nutrients
what does the cytoplasmic membrane do?
- separates the inside (cytoplasm) of the cell from the outside (periplasm or cell wall), a permeability barrier
- ETC occurs in the cell membrane
- built of fatty acids (hydrophobic) and glycerol (hydrophilic)
- lots of enzymes involved in metabolism reside in the cell membrane
What are the 2 types of bacterial cell wall?
gram-positive: thick cell wall. no outer envelope. acidic polysaccharides
gram-negative: thinner cell wall. has an outer envelope. lipopolysaccharide-rich outer layer
all contain peptidoglycan (polymer of polysaccharides linked by proteins
What constitutes the cell envelope?
capsule
EPS (inc. enzymes and cells)
sheaths
S-layers
What is EPS and what is its function
EPS = extracellular polymeric substances extracellular = outside the cell polymeric = organic polymer (carbon) substances = to imply there's different types
mostly made of polysaccharides, glycoprotein
produced inside the cell and excreted through the cell wall
on species can make different EPS dependent on their environment or different growth stages
function:
buffer from changes in environmental conditions
adherence to surface and stability of colony
are and energy and carbon source
What are sheaths?
- Act like a sieve to protect the cell from large molecules
- can have different surface charges to the cell, acting as a mediator between the cell and the environment
- so can have different interactions with the cell wall and cell environment than the cell would have without the sheath
What are S-layers?
s-layers = structural layers. more organised than EPS or sheaths
paracrystalline (sort of crystalline but not quite)
similar role to sheaths (protection) but different composition and structure
can have different surface charges - can prevent or encourage metal sorption
can shed metal-encrusted S-layers
What are functional groups? and what is their role for microbes?
functional groups = specific groups of atoms or binds within organic molecules that are responsible for characteristic reactions e.g., -OH (alcohol functional groups)
functional groups interact with the environment
what are the microbial surface charges in a low pH environmental?
- most functional groups are protonated
- net charge of cell surface is neutral or positive
- hydrophobic
- attracts neutral or negatively charged ions (anions)
- attracts ligands well –> ligands are negatively
what are the microbial surface charges in a high pH environment?
- functional groups are deprotonated
- average bacterial surface is negatively charged
- attracts cations (positively charged)
- hydrophilic
what is the pHZPC
pH of zero point charge
the pH at which the surface charge = 0
what are the steps of adhesion and attachment?
- Transport of bacteria to a surface (diffusion, advection, motility, chemotaxis)
- initial adhesion via electrostatic attraction
ions held 10-15 nm from cell surface - Irreversible attachment to the surface. some cells attach via appendages (pili, fibrils, hypeae)
what are the steps of adhesion and attachment?
- Transport of bacteria to a surface (diffusion, advection, motility, chemotaxis)
- initial adhesion via electrostatic attraction
ions held 10-15 nm from cell surface. EPS excreted to bridge gap. strength and affinity of interaction depends on surface characteristics. - irreversible attachment via excretion of EPS of appendages
