Extreme Environments II: thermophiles and psychrophiles

Question 1

nomenclature – a crash course!

Answer 1

• thermophiles – require high temperature to grow.
• psychrophiles* – require low temperature to grow.
• thermotolerant organisms can cope with high temperature.
• psychrotolerant (same idea).
• extreme thermophiles
• mesophiles grow at ambient temperature or not much
  higher/lower.
  [* ‘cryophiles’ was used at one time – long gone now]
  Recent changes: Psychrotolerant organisms are often now called eurypsychrophiles, where as true psychrophiles are
  stenopsychrophiles.

Question 2

temperature and water

Answer 2

• at low temperatures (and high pressures), ices form. Many types of ice – ice is technically a mineral, there is a Pourbaix diagram for water.
• as you approach ice, water becomes more viscous: solute transfer and movement is going to become much slower. Gases dissolve more easily in cold water but other solutes less easily.
• as water boils dissolved gases become less soluble and leave the system – important for gas-using organisms. Other solutes become more soluble.
• water near to boiling is less viscous

Question 3

Arrhenius equation

Answer 3

• temperature ranges of growth obey the Arrhenius function if growth rate is studied (does not apply if yield is used instead!):
  K=rate constant for the reaction (µ)
  T = absolute temperature (in K)
  R = universal gas constant (8.31446 J/K/mol)
  A = the pre-exponential factor (doesn’t mean
  much!)
  e = Euler’s number (2.71828)
  Ea = activation energy of the reaction (in J/mol)
  What is the Arrhenius equation K equal to?
  k=Ae^ −EA/(RT)

Question 4

Arrhenius functions of growth

Answer 4

optimum temperature is 35 °C (corresponds to 0.00324 on x-axis below).
In the range just below this (i.e. right of it on below plot):
gradient = -Ea
/R = -5759.6 thus Ea = 47.9 kJ/mol.
y-intercept (if you continue the line) = ln A = 4.42, thus A = 83.09 [not very useful – has no real meaning!

Question 5

temperature quotient (Q10)

Answer 5

• used a lot in food microbiology/food safety – makes
  it easy to estimate organism-count at a given
  temperature.
• also applies to plants/animals
• Q10 = change in µ per 10 °C increase below
  optimum temperature.
• determined based on measuring µ at 2
  temperatures, 1 high (“H”) and 1 lower (“L”)

Question 6

high temperature ecosystems

Answer 6

• mining leach-heaps (80 °C)
• compost heaps (50-77 °C)
• rotting corpses (up to 45 °C)
• biogas bioreactors (55 °C)
• domestic oven (up to 220 °C)
• volcanic mud (70 °C)
• volcanic lakes (up to 110 °C)
• thermal springs:
  -Roman Baths, Bath, UK (45 °C)
  -Movile Cave, Romania (40 °C)
• geysers (up to 110 °C)
• domestic heating systems (up to 70 °C)
• solfatare (“mud-pots”, 95-110 °C)
• deep-sea hydrothermal vents (up to 400 °C)
• anywhere heated by sun e.g. salterns

Question 7

what does high temperature do to Life?

Answer 7

PROTEINS:
* unfold, losing secondary to quaternary structure, denaturing; at very low pH, primary structure is lost through hydrolysis of peptide bonds; loss of enzyme function and structural integrity.
LIPIDS:
* bilayers lose integrity – ‘melting’.
* eventually hydrolysis into fatty acids and e.g. phosphoglycerate.
NUCLEIC ACIDS:
* loss of base-base hydrogen bonds in rRNA and DNA, both of which ‘melt’, AT-rich regions first.
* DNA and RNA hydrolyse into oligonucleotides and individual bases at very high temperature

Question 8

what does high temperature do to Life?

Answer 8

ENVIRONMENT:
* metals generally become more soluble, gases become less soluble.
* think about consequences for an organism that grows on gases as energy and carbon source – how might they get around that?
EXAMPLE BUGS:
Thermithiobacillus tepidarius - a CBB chemolithoautotroph that can use S-compounds. Found in Roman Baths at Bath and on rotting concrete in sewers in Melbourne. Grows at 45 °C.
Thermotoga maritima – a fermenter that grows anaerobically– has a ‘toga’ around cells for unknown reasons
Methanopyrus kandleri from the Archaea, some strains grow at 122 °C and stay alive at 129 °C. cf.

Question 9

adaptations to high temperature

Answer 9

DNA: generally a higher G+C fraction than mesophiles or
psychrophiles but not always true. Proteins that stabilise DNA also present.
PROTEIN: elevated amounts of chaperones and chaperonins.
Elevated amount of disulfide and trisulfide bridges versus mesophiles or psychrophiles; elevated amounts of isopeptide bonds versus mesophiles and psychophiles. More glycosylations of proteins to add stability. Presence of polyamines e.g. thermamine, thermine to protect
proteins from unfolding. Metals buried deeper.
LIPIDS: shift towards more saturated fatty acids (stable to melting to higher temperature), hydroxylated fatty acids and ω-cyclohexyl fatty acids. Most extreme thermophiles are Archaea.

Question 10

low temperature ecosystems

Answer 10

• domestic refrigerators (+4 °C) and freezers (-18 °C) and laboratory freezers (-78 °C)
• ice-brines (-10 °C to -5 °C)
• polar ice-caps (0 °C down to -20 °C but varies)
• McMurdo Dry Valleys, Antarctica (-30 °C)
• Vostok Station, Antarctica (-89.2 °C)

Question 11

what does low temperature do to Life?

Answer 11

PROTEINS:
* ‘tighten’ up, becoming less flexible and thus losing catalytic ability or at least slowing down a lot.
LIPIDS:
* bilayers become brittle.
NUCLEIC ACIDS:
* similar to proteins – H-bond strength increases so uncoiling is so much more effort.
METABOLISM:
* water is more viscous, gases are very soluble, salts are not – moving things from enzyme to enzyme is slow.
* ice crystals forming in cells can burst them open when they thaw.

Question 12

what does low temperature do to Life?

Answer 12

EXAMPLE BUGS:
Flavobacterium psychrophilum - a generalist
chemoorganoheterotroph. Pathogen in cold-water fish. Grows best below +16 °C. Yellow.
Janthinobacterium lividum – a generalist chemolithoheterotroph found in rivers etc. Grows best below +16 °C. Violet.
Planococcus halocryophilus grows at -16 °C and stay alive at -25 °C

Question 13

low-temperature adaptations

Answer 13

PROTEINS:
* structures tend to have fewer isopeptide bonds, di-/trisulfide bridges and ionic interactions than mesophiles so as to ensure flexibility.
LIPIDS:
* higher proportion of (poly)unsaturated fatty acids to keep membrane supple at lower temperatures.
NUCLEIC ACIDS:
* lower G+C fraction than mesophiles (not always the case) to ensure reduced H-bonding between the strands.
METABOLISM:
* enzyme-clustering/substrate-channeling to overcome viscosity issues.
* cryoprotectant proteins to prevent ice-nucleation as well as
cryoprotectants such as glycerol, sugars, sugar alcohols and DMSP and betaine and choline (and maybe TMA N-oxide too).