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 mind-

1. 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)ThermophilesUpper temperature limits for life:Animals 50ºC (insects, ostracods)Plants 50ºC (mosses)Fungi 62ºCBacteria 95ºCArchaea 121ºC (Pyrodictium)

Absolute limit: ???(but ATP, NAD+ unstable at 150ºC)

Molecular adaptations:

thermostable proteins• 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• saturated fatty acids (Bacteria)• di-alcohol (Thermomicrobium)• ether bonds + isoprenes (Archaea)• lipid monolayer (Archaea)

Archaeal Membrane Lipids

Bacterialglycerol diesterR = fatty acids

neutrophiles:majority of Bacteria

man

y fu

ngi

Picrophilus: pH 0.7AcidithiobacillusThiobacillusSulfolobusCyanidium (red algae): pH 2

1M HCl

Bacillus firmushalophilic Archaea→ Na+ gradient

(“SMF” instead PMF)

pH

S-oxidizer

Factors Affecting Growth (Rate)

• Temperature• pH• Salinity/

Water Activity• Oxygen• Pressure• Radiation• Nutrition

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…)

yeasts, fungi,halophilicArchaea

xerophilic fungi

some Gram-positives

e.g. Vibrio fischeri

e.g. E.coli

0.600 Honey

Salinity – Water Activity

3% 15-30%1%

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 internalsolute concentrationby compatible solutes

1) pump inorganic ions (e.g. K+) into the cell

2) organic solutes:non-inhibitorywater soluble

”Small Compatile Solutes”

Factors Affecting Growth (Rate)

• Temperature• pH• Salinity/

Water Activity• Oxygen• Pressure• Radiation• Nutrition

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

oxidizedresazurinreduced

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• pH• Salinity/

Water Activity• Oxygen• Pressure• Radiation• Nutrition

Short wavelength radiation (<340nm) destroys cell compounds (incl. DNA).

Light (esp. UV) + O2 + cytochromes → 1O2Carotenoids quench 1O2 (and absorb light).

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

UV causes thymine dimers in DNA, and such damage needs enzymatic repair.

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

KSKS

Gro

wth

rate

µ

µmax

½ µmaxµmax

½ µmax K-strategist

r-strategist µ = µmax · [S]

KS + [S]

substrateaffinity of thestrain:

A =µmax

KS

Advantage for K-strategist

Advantage forr-strategist