5. Biofilms Flashcards
what is a biofilm
a highly concentrated conditioning film of nutrients which draws bacteria to them
when bacteria arrive at a biofilm and attach what do they adapt?
a sessile phenotype
what are the three methods that bacteria arrive at a biofilm through
- diffusion
- chemotaxis
- turbulence impaction
explain how bacteria arrive at a biofilm through chemotaxis
bacteria are drawn towards a surface, they use their flagella to propel them towards the surface
explain how bacteria arrive at a biofilm through turbulence impaction
turbulence brings the bacteria right to the surface
bacteria exist in laminar flow,, what is this?
particles flow in smooth, distinct layers where there is no mixing
what does the boundary layer do
here there is no flow, it facilitates diffusion of bacteria that drop out of laminar flow
what occurs during turbulent flow
there is lots of mixing, the boundary layer is disturbed bringing the liquid right to the surface = binding
what type of surface does turbulent flow work better with, why?
rough surfaces over smooth surfaces
- there is more surface area = more binding opportunities
describe the mechanism of bacterial attachment to a surface
both molecules are negatively charged and so bacterial cell gets repelled
bacterial cell then hovers over the surface
bridging structures called adhesins then connect the bacterium to the surface
name 4 adhesins
flagella, pili, fimbriae, stalks, adherence proteins
what do bacteria produce that prevents them from being flushed following attachment
their own glue rich in sugars
- this is termed the matrix
- and is the beginning of the biofilm
what happens following attachment
adoption of a sessile phenotype
what does adoption of a sessile phenotype mean
50-60 changes in genes:
- down regulation of planktonic genes
- up-regulation of sessile genes
what are planktonic genes
swimming genes (e.g. flagella)
what are sessile genes
genes that help you live in a biofilm, e.g. stress proteins, capsule
what genes are involved in producing this glue
Alg genes
what % of the biofilm matrix is water
98%
what provides structure and integrity to the matrix
exopolymeric substances (EPS)
what do channels in the biofilm allow
allow fresh liquid into the biofilm (nutrients/ oxygen)
removes waste products
how do top-heavy biofilm stacks form
disproportionate levels of oxygen and nutrients reach the top layer = higher bacterial growth + EPS production
what happens to a biofilm with low flow & low nutrients
slow compact growth
what happens to a biofilm with high flow & high nutrients
rapid growth, prone to sloughing. (unstable)
what are cells embedded in the matrix protected from
predation (macrophages)
antimicrobial compounds
increased flow rates
