Download Extremophiles -what does that mean?

Extremophiles
-what does that mean?
Questions :
1. Why are we interested in extremophiles?
2. What are the challenges associated with life under
extreme conditions (extremely hot/cold, acidic/alkaline,
dry/salty etc.)?
3. How do microbes cope with them?
Why extremophiles?
We usually have two extraterrestrial
habitats in mind1. Mars
2. Europa
What is considered an
Analogue -and to what- some
examples ?
-
Black smokers
Deep biosphere
Dry (cold) desserts
Permafrost Soil
Microbial Growth
Factors Affecting Growth (Rate)
• Temperature
• pH
• Salinity/
Water Activity
• Oxygen
• Pressure
• Radiation
• Nutrition
 higher growth rate (µ) with higher Temp.
 µ doubles for each 10ºC (Q10 = 2)
 limited temperature range for a given
bacterium (~10 to 40 ºC)
 cardinal temperatures
Temperature Classes
Cold temperature challenge: - keep membranes and proteins flexible
- maintain transport across membranes
→ polyunsaturated fatty acids
Hot temperature challenge:
- denaturation of proteins
- fluidization of membranes
(Hyper)Thermophiles
Upper temperature limits for life:
Molecular adaptations:
Animals
50ºC (insects, ostracods)
 thermostable proteins
Plants
Fungi
50ºC (mosses)
62ºC
Bacteria
95ºC
Archaea
121ºC (Pyrodictium)
•
•
•
•
few AA substitutions: folding
more ionic bonds
protective solutes in cytoplasm
chaperonines (“thermosomes”)
 DNA stability
• protective solutes
• reverse DNA gyrase: +supercoils
• DNA-binding proteins
 membrane stability
Absolute limit: ???
(but ATP, NAD+ unstable at 150ºC)
•
•
•
•
saturated fatty acids (Bacteria)
di-alcohol (Thermomicrobium)
ether bonds + isoprenes (Archaea)
lipid monolayer (Archaea)
Archaeal Membrane Lipids
Bacterial
glycerol diester
R = fatty acids
many fungi
1M HCl
Picrophilus: pH 0.7
Acidithiobacillus
Thiobacillus
S-oxidizer
Sulfolobus
Cyanidium (red algae): pH 2
neutrophiles:
majority of Bacteria
Bacillus firmus
halophilic Archaea
→ Na+ gradient
(“SMF” instead PMF)
pH
Factors Affecting Growth (Rate)
• Temperature
• pH
• Salinity/
 water availability is measured as
water activity aW = Psolution / Ppure water
(P = vapor pressure)
 depends on:
• water content (wet/dry)
• concentration of solutes (salt, sugar…)
Water Activity
• Oxygen
e.g. E.coli
• Pressure
e.g. Vibrio fischeri
some Grampositives
• Radiation
• Nutrition
0.600
Honey
yeasts, fungi,
halophilic
Archaea
xerophilic fungi
Salinity – Water Activity
 osmosis: water diffuses to the place of lower water concentration
 cytoplasm with higher solute concentration than surroundings
→ water diffuses into the cell (positive water balance)
 low aW → water diffuses out of the cell: dehydration, dormancy, death
• food conservation: lower aW (addition of salt, sugar)
• nature: saline environments
• adaptation:
increase the internal
solute concentration
by compatible solutes
1) pump inorganic ions (e.g.
K+) into the cell
2) organic solutes:
non-inhibitory
water soluble
1%
3%
15-30%
”Small Compatile Solutes”
Factors Affecting Growth (Rate)
• Temperature
• pH
Oxygen is a super parameter for all types of life
– either because it is the best electron acceptor
available
– or because it is a terrible poison
• Salinity/
Water Activity
• Oxygen
• Pressure
• Radiation
• Nutrition
oxidized
resazurin
reduced
Oxygen
 Examples of
•
obligate aerobes: Micrococcus luteus
•
obligate anaerobes: Clostridium, Methanobacterium
•
facultative aerobe: E. coli, Pseudomonas fluorescens
•
microaerophiles: Spirillum, magnetotactic bacteria
•
aerotolerant: Streptococcus, some sulfate-reducing bacteria
 Oxygen toxicity:
•
singlet oxygen (1O2), by photochemical/biochemical reactions
•
O2- as by-products of flavoproteins, quinons, thiols, Fe-S proteins
•
by-products of oxygen metabolism:
Oxygen Detoxification
 Singlet oxygen: carotenoids (phototrophs, airborne bacteria)
 Hydrogen peroxide: catalase, peroxidase
 Superoxide: superoxide dismutase, superoxide reductase, Mn2+
Factors Affecting Growth (Rate)
• Temperature
• pH
• Salinity/
Water Activity
• Oxygen
• Pressure
• Radiation
• Nutrition
 Barophilic bacteria grow best at high pressure.
 Pressure increases by 1 atm per 10 m water
depth; pressure effects start at >2000 m.
 In the depth of the Oceans (average ocean
depth, 5 km ~ 500 atm) a large niche is found for
barophiles. The physical and chemical nature
of organic matter including enzymes,
membranes and cell walls is changed at such
pressures.
Factors Affecting Growth (Rate)
• Temperature
 Short wavelength radiation (<340nm)
destroys cell compounds (incl. DNA).
 Light (esp. UV) + O2 + cytochromes → 1O2
Carotenoids quench 1O2 (and absorb light).
• pH
• Salinity/
Water Activity
• Oxygen
• Pressure
• Radiation
• Nutrition
UV causes thymine
dimers in DNA, and such
damage needs enzymatic
repair.
Gamma radiation is usually
sterilizing, but some
organisms may tolerate
incredible doses, >15,000 Gy
(Deinococcus radiodurans).
[humans are killed by <10
Gy] Gy = Gray = J/kg
Factors Affecting Growth (Rate)
• Temperature
• pH
• Salinity/
Water Activity
• Oxygen
• Pressure
• Radiation
• Nutrition
 Growth rate is dependent on enzymatic
conversions and transport processes
 these are most often dependant on the
substrate concentration (Michaelis-Menten)
Michaelis-Menten-Kinetics: competition
Growth rate µ
µmax
r-strategist
µmax · [S]
µ=
KS + [S]
½ µmax
µmax
K-strategist
½ µmax
KS
Advantage for
K-strategist
KS
Advantage for
r-strategist
substrate
affinity of the
strain:
µmax
A=
KS