Extremos de Vida: Ambientes e Organismos que Resistem Condições Extremas, Notas de aula de Astrobiologia

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Life Through

Time

LIFE IN EXTREME

ENVIRONMENTS

How do we define ‘extreme’?

 What is extreme to us may not be to others…

Is it just a matter of taste or is there more to it?

 Conditions on the Early Earth were ‘extreme’

‘Extremophiles’

 Organisms that tolerate or require extreme conditions  Mostly prokaryotes (bacteria and archaea) but also eukaryotes  Biological systems only function within a certain continuum of physical and chemical parameters

Hot environments

 Thermophiles (50 – 80 °C) and hyperthermophiles (above 80 °C)

Methanopyrus kandleri

An archaea that inhabits black smokers (up to 110 °C)

Challenges

 Breakdown of biomolecules  Increased membrane fluidity

Adaptations

 Thermostable proteins and enzymes  Modified cell membrane composition

Freezing environments

Cold-loving (‘psychrophilic’)

microorganisms (<15 °C)

Lake Vostok accretion ice houses a surprisingly complex community of cold-tolerant bacteria and fungi

Challenges

 Membrane damage from ice  Decreased membrane fluidity  Availability of liquid water

Adaptations

 Membrane composition (again)  Antifreeze agents

Extremes of pH

 Acidophiles (pH 0.4 – 4) and alkaliphiles (pH 8 – 12.5)

Acidic mine drainage (Rio Tinto) Alkaline freshwater (Mono Lake) Challenges  Breakdown of cellular components  Limitations to metabolic processes Adaptations  Regulation of internal pH  Both active and passive

Living under high pressure Trenches in the Pacific, e.g. Mariana Trench (11 km)  Piezophilic (‘pressure-loving’) microorganisms (up to 1300 × atmospheric pressure) Challenges  Tight packing of molecules and loss of fluidity  Impaired cellular structures and activities Adaptations  Changes in gene expression and membrane structure  Comparatively poorly understood The deep sea: 75% of ocean volume Life also persists in the deep, rocky subsurface

Extremes rarely occur in isolation!

 Studies of extremophiles often too simplistic

 ‘True’ environments frequently characterised by multiple extremes

 Polyextremophiles

Deinococcus radiodurans

Tolerates…

 High levels of radiation  Cold temperatures  Dry environments  Vacuum conditions  Acidic pH levels

One extreme can influence ability to tolerate

another

Terrestrial analogues for other planets?

Mars Europa Enceladus Titan