L23

Question 1

what is biofilm

Answer 1

• microbial cells + associated extracellular polymer firmly attached to a submerged surface in a aquatic environment (contain community of bacteria, fungi etc.)
• contains inorganic or abiotic substances in biotic matrix
• 99% of bacteria like in biofilm
• vary in thickness, from monolayer of 400mm (algal mats)
• ## can be established quickly

Question 2

why do bacteria form biofilms

Answer 2

• defence from physical force (like water rushing past) and toxic molecules
• provides a favourable niche (grab nutrients as it goes past)
• communal living

Question 3

what is quorum sensing

Answer 3

• method of cell to cell communication between bacteria
• secretes autoinducer (AI) molecules
• at low cell no.s, AI produced but no evidence of cell to cell communication, as AI diffuses in surrounding environment
• at higher cell numbers (quorum) AI enters cells, binds to a specific activator protein, leads to gene expression
• important factor in pseudomonas auruginosa biofilm production
• triggers the expression of a alrge no. of unrelated genes when pop. density reaches a sufficiently high value
• requires more then 10^5 CFU/G

Question 4

disease, industrial, biotech, and environmental examples of biofilm

Answer 4

• cystic fibrosis
• sewage + diary industry
• medicine, food additives
• corrosion, rust, plant roots

Question 5

how are biofilm formed

Answer 5

• nutrients adsorbed to the surface, form a conditioning film
• microorganisms attach to conditioned surface
• growth + division + exopolysaccharides create coverage
• thickening
  -sloughing

Question 6

list beneficial biofilms

Answer 6

• fermentation: acetate acid production
• metal leaching: mining undustry for conc. of low grade ore
• wastewater treatment: create conditions favourabel for biofilm production, will atrract bacteria + nutrients, therefore purifying water

Question 7

list detrimental biolfilms

Answer 7

food safety: as biofilm matures, sloughing occurs, resulting in food contamination/ reduce shelf life

corrosion: biofilm aids electrochemical processes by producing metabolic products (e.g. lactic acid), areas of various thickness results in formation of differential aeration cells + local anodes (anaerobic sites) + cathodes (aerobic sites)

turbulence: due to apparent surface roughness, leads rto decreased lifespan, icnreased costs, energy loss, reduced performance

heat transfer inefficiency: may render heat exchanger inoperative

Question 8

what are SRB

Answer 8

• sulphate reducing bacteria
  -group of anaerobic bacteria that form biofilms
• bacteria that reduce sulphate to sulphides
• TIO2 film protects

Question 9

explain metal corrosion

Answer 9

• oxidation of iron (anode) and reduction of oxygen (cathode) on surface of metal, causes loss of mass (rust)
• Fe2 oxidsed further into Fe3, then Fe(OJ)3, then converted into iron oxides
  -20% of corrosion is microbe mediated- e.g. SRB + acid producing bacteria
• bacteria that retards corrosion- manganese fixing bacteria, acetate oxidisng bacteria,a cetate producing bacteria

Question 10

explain how to clean biofilms

Answer 10

• clean with detergent + physical force
• disinfect
• remove dead microbes ( cause will act as a nutrient for biofilm to regrow)