Lecture 7' Microbial Adaptations 2

1
Lecture 7. Microbial Adaptations 2

• Alkalophiles an excess of protons
• Radioresistance molecular stability
• Barophiles pressure responses
• Oligotrophs high affinity uptake

2
Alkalophiles

• Organisms growing optimally at pH 8.5 11
• Very widely distributed in the environment
• Archaea prevalent in haloalkaline (soda) lakes
  (Natronococcus, Natronobacterium)
• Include bacteria (Bacillus alkalophilus, B.
  firmus), fungi, yeasts

3
Problems and Solutions

• Na-dependent solute transport
• High affinity proton transport systems
• Reversed pH gradient
• Extracellular and periplasmic enzymes adapted to
  function at high pH

• High external Na
• Low external H
• High external pH
• Instability of external proteins

4
Maintaining a Proton Motive Force

• A PMF is used for ATP synthesis (protons are
  pumped out of the cell, and drive ATPase on
  reentering)
• PMF is comprised of a pH gradient (DpH) and
  electrical membrane potential (charge difference
  D?)
• A cell cannot change PMF, but can adjust DpH and
  D?.

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Maintaining a positive PMF
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pH homeostasis, ATP synthesis and solute
transport in neutrophiles and alkalophiles
H
Substrates
Na
Substrates
H
H
H
Na
ATP
ATP
Respiration
Respiration
pH 7
pH 7.5
H
pH 7
pH 10
H
Neutrophiles
Alkalophiles
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Radioresistant organisms

• Ability to live in the presence of high levels of
  ionising radiation
• High energy radiation damages macromolecules
• DNA damage is most critical
• Deinococcus radiodurans can survive 3 MRad
  radiation (humans are killed by 100 Rad)
• Primary adaptation is a hyper-active DNA repair
  system (RecA)
• Many other DNA repair mechanisms

8
Barophiles

• Organisms living at high pressures
• Barophiles versus barotolerants
• Organisms living in abyssal oceans
• High pressure affects the thermodynamics of
  reactions involving volume changes
• High pressure stabilises three-dimensional
  molecular structures

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Oligotrophy

• Growth at very low nutrient concentrations
• Oligotrophic environments are widespread
  (copiotrophic environments are relatively rare by
  comparison)
• Marine water contains 1-6 mg C.l-1 cf Nutrient
  Agar 4000 mg C.l-1
• Numerous species of bacteria, fungi and yeasts

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Problems and Solutions

• Low growth rates
• Low S concentrations
• Sudden changes in S concentrations

• Not a problem
• High affinity uptake systems (Ks values for
  glucose, acetate etc. lt 1 mM have been recorded).
• Oligotrophs have both H and L affinity uptake
  mechanisms

11
Determination of saturation constants for growth
(Ks)
1/Growth rate
Growth rate (h-1)
-1/Ks
Substrate concentration
1/Substrate concentration
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Glucose affinities for oligotrophs and copiotrophs