MICB Lecture 6

• biofilms

  In nature, this is how microbes grow

  defined as microbial communities attached to a surface covered with a protective matrix
• Stages

  to make mature biofilm

  A) planktonic

  B) attach

  C) colonization

  D) maturation

  E) dispersal

  
• Intelligent implants

  sensors send and alert when they detect bacteria

  chip sends instructions to treat infection

  reservoir contains antibiotic that stops individual bacteria and kills it
• dental plaque

  microbial film on tooth surface (>300 microbial species)
• caries

  tooth decay

  bacterial fermentation -> acidic products -> enamel

  example: streptococcus mutans
• periodontal disease

  microbial infection with inflammation, tissue destruction

  ex: porphyromonas gingivalis
• Environmental factors that influence microbial growth

  oxygen concentration

  temperature

  solutes and water activity
• Microbes and oxygen concentrations

  obligate aerobe: needs oxygen

  facultative anaerobe: prefers oxygen

  aerotolerant anaerobe: ignore oxygen

  oligate anaerobe: oxygen toxic

  microaerophile: prefers oxygen in 2-10% range

  A) obligate aerobe

  B) facultative anaerobe

  C) aerotolerant anaerobe

  D) obligate anaerobe

  E) microaerophile

  
• oxygen can be reduced to toxic products called reactive oxygen species (superoxide radical and hydrogen peroxide). Microbes that live in the presence of oxygen need enzymes to detoxify.
• Reactive oxygen species

  Enzymes

  • Superoxide dismutase (SOD)
  • Catalase

  A) catalase positive

  B) catalase negative

  
• Hyperthermophiles

  grow between 85 and 113C
• thermophiles

  grow between 45-85C

  ex: thermus aquaticus (bacteria)

  • source of taq polymerase
• mesophile

  grow between 20-45C

  ex: Escherichia coli
• Psychrophiles

  grow between 0-20C
• Pink snow

  due to snow algae

  genus: Chlamydomonas

  
• How do thermophiles adapt

  Proteins stabilize

  increased H bond and covalent bonds, molecular chaperones bind and refold damaged proteins

  DNA stabilizes

  synthesize proteins to coat DNA

  Membrane stabilizes

  more saturated, branched, and have higher MW, archaeal membranes have rigid, stable monolayers and ether linkages that make them resistant to hydrolysis at high temperatures
• Microbes grow under a wide range of solute concentrations: solutes like salts and sugars decrease the availability of water to microbes
• Water activity

  availability of water affects growth of all cells, higher [solute] = lower water activity (aw)
• hypotonic osmosis

  Low extracellular solute concentration

  ex: freshwater lake or stream

  
• Isotonic


  same solute concentration in and out

  
• hypertonic

  high extracellular [solute]

  low aw

  ex: dead sea, great salt lake, peanut butter
• halophile

  require high [salt] to grow
• osmotolerant

  grow over wide range of aw

  ex: staphylococcus - salt tolerant commensal of human skin, mannitol salt agar to select
• xerophile

  grow at low aw and dry conditions

  A) cronobacter

  
• How do microbes survive in highly concentrated environments

  use compatible sources

  ex: KCl, betaine, some amino acids (proline)