Life in the ColdLife in the Cold

Neill ReidNeill Reid

STScI & Maryland STScI & Maryland Astrobiology Astrobiology ConsortiumConsortium

Maryland Astrobiology Maryland Astrobiology ConsortiumConsortium

STScISTScI

Mark Clampin (GSFC)Mark Clampin (GSFC)Mario LivioMario LivioSteve LubowSteve LubowMelissa McGrath (now Marshall)Melissa McGrath (now Marshall)Keith NollKeith NollAntonella NotaAntonella NotaNeill ReidNeill ReidKailash SahuKailash SahuBill SparksBill SparksJeff ValentiJeff Valenti

COMB, UMDCOMB, UMD

Bob Belas Bob Belas Rick Cavicchioli (Univ. NSW)Rick Cavicchioli (Univ. NSW)Feng ChenFeng ChenAlbert ColmanAlbert ColmanShil DasSarmaShil DasSarmaPriya DasSarmaPriya DasSarmaJochen MullerJochen MullerFrank RobbFrank RobbKevin SowersKevin SowersHem ShuklaHem Shukla

OutlineOutline

Pushing the limits of the habitable zonePushing the limits of the habitable zone o Cold environments on EarthCold environments on Eartho Cold environments in the Solar SystemCold environments in the Solar Systemo Environments of extrasolar planets Environments of extrasolar planets

Terrestrial analogues for extraterrestrial Terrestrial analogues for extraterrestrial lifelife

Initial experimental resultsInitial experimental results

The classical habitable The classical habitable zonezone

Definition: Definition: the circumstellar region where water the circumstellar region where water can exist in liquid form on the surface can exist in liquid form on the surface of a planet.of a planet. ~ 0.8 to 1.4 AU in the Solar System~ 0.8 to 1.4 AU in the Solar System

The habitable zone The habitable zone evolves as Levolves as Lsunsun evolves evolves

“ “continuous habitable continuous habitable zone”zone”

Can life survive and replicate beyond these limits?Can life survive and replicate beyond these limits?

Terrestrial life in the coldTerrestrial life in the coldWe view Earth as a temperate environment, but 95% of the biosphere exists at T < 5oC Recent investigations show evidence for extensive species diversity, notably at the microbial level

The Solar System - MarsThe Solar System - Mars

Mars ain’t the kind of place to raise your kidsMars ain’t the kind of place to raise your kidsIn fact, it’s cold as hell….. In fact, it’s cold as hell….. B. Taupin B. Taupin Canyon gullies in HellasCanyon gullies in Hellas

Mars lies beyond the current HZ, but probably still has substantial sub-surface water – and temperatures can rise above freezing

The Solar System - EuropaThe Solar System - Europa

Europa lies at 5 AU from the Sun, well beyond the conventional habitable zone – but there is an alternative energy source: tidal heating by Jupiter. Measurement of Europa’s magnetic moment strongly suggests the presence of an extensive sub-surface ocean beneath a moderately-thick (3-4 km?) icy crust.

Extrasolar planets - Extrasolar planets - statisticsstatistics

• 143 planets in 125 ‘normal’ planetary 143 planets in 125 ‘normal’ planetary systemssystems

o 5 discovered in transit surveys5 discovered in transit surveyso 1 by gravitational microlensing1 by gravitational microlensingo 119 by radial velocity surveys119 by radial velocity surveys

• There are at least 15 multi-planet systems There are at least 15 multi-planet systems (indications of others from long-period trends)(indications of others from long-period trends)• Lowest mass planet: Gl 436b, Lowest mass planet: Gl 436b, MM~0.067~0.067MMJJ or or ~21~21MME E – Neptunian-mass companion of a – Neptunian-mass companion of a nearby M dwarfnearby M dwarf• Shortest period systems: P~1.2 days, Shortest period systems: P~1.2 days, a~0.015 AUa~0.015 AU• Longest period systems: Longest period systems: PP ~ 8 years, ~ 8 years, aa ~ 4.2 ~ 4.2 AUAU

Extrsolar planets - hostsExtrsolar planets - hostsMost stars with detected Most stars with detected planets are similar to the planets are similar to the Sun –Sun – Masses ~ 0.8 to 1.2 Masses ~ 0.8 to 1.2 MMsunsun

Most are H-burning main Most are H-burning main sequence stars – some sequence stars – some giants and 2 low-mass M giants and 2 low-mass M dwarfsdwarfs

Partly reflects bias in Partly reflects bias in radial velocity surveys – radial velocity surveys – we’re looking for planetary we’re looking for planetary systems like our own (and systems like our own (and solar type stars are good solar type stars are good targets for Doppler surveys)targets for Doppler surveys)

Extrasolar planet environmentsExtrasolar planet environmentsPlanetary temperatures Planetary temperatures

depend on:depend on:1.1. Luminosity of central Luminosity of central

starstar2.2. Distance from central Distance from central

starstar3.3. Planetary atmosphere Planetary atmosphere

(albedo and greenhouse (albedo and greenhouse effect)effect)

1+2 1+2 substellar substellar temperature temperature

For Earth, TFor Earth, TSSSS = 394K = 394K equilibrium temperature:equilibrium temperature: TTeqeq = 279 K, 6 = 279 K, 6 ooCC

Many extrasolar planets Many extrasolar planets have eccentric orbits, so have eccentric orbits, so TTeqeq changes significantly changes significantly over the planetary ‘year’over the planetary ‘year’

Extrasolar planets - Extrasolar planets - temperaturestemperatures

TTeqeq scales with period, since most hosts are solar-type scales with period, since most hosts are solar-type starsstars

Average TAverage Teqeq ranges from ~1100 ranges from ~1100ooC for ‘hot Jupiters’ to -C for ‘hot Jupiters’ to -150150ooC for Jovian analogues; systems on eccentric C for Jovian analogues; systems on eccentric orbits have significant annual variations.orbits have significant annual variations.

Extrasolar planets – habitable Extrasolar planets – habitable zoneszones

~40 known planets spend part ~40 known planets spend part of their orbit within the of their orbit within the habitable zone of their habitable zone of their primaryprimary

Over 10 planets are within the Over 10 planets are within the habitable zone for the most habitable zone for the most orbit – although most have orbit – although most have high e and large T range. high e and large T range. Best prospect (?):Best prospect (?):

HD 28185, G5, 5.6 MHD 28185, G5, 5.6 MJ J planet in planet in

1.0 AU orbit, e=0.061.0 AU orbit, e=0.06 -1 < T < 16-1 < T < 16ooC C Large gas giant – but what Large gas giant – but what

about satellites?about satellites?

Life at the extremesLife at the extremesArchaeal and bacterial prokaryotic life Archaeal and bacterial prokaryotic life supplies most of the biodiversity in supplies most of the biodiversity in extreme environments:extreme environments:

High temperatures:High temperatures: thermophiles – growth at 40 to 80thermophiles – growth at 40 to 80ooCC hyperthermophiles - growth at T > 80hyperthermophiles - growth at T > 80ooCC

Room temperature:Room temperature: Mesophiles – optimal growth at 20 to Mesophiles – optimal growth at 20 to 4040ooCC

Low temperatures: Low temperatures: Psychrotrophs - optimal growth at T > Psychrotrophs - optimal growth at T > 2020ooC, but can grow at temperatures C, but can grow at temperatures between ~0 and 20between ~0 and 20ooCC

Psychrophiles - optimal growth at T < Psychrophiles - optimal growth at T < 1515ooCC

Pushing life’s limits: Pushing life’s limits: psychrophiles as ET analoguespsychrophiles as ET analogues

Physiological adaptation to cold:Physiological adaptation to cold: Accumulation of osmolytes (sugars, polyols, amino acids, inorganic Accumulation of osmolytes (sugars, polyols, amino acids, inorganic

ions) – protection against freezingions) – protection against freezing Alteration of lipids in membranes to give increased fluidity (e.g. Alteration of lipids in membranes to give increased fluidity (e.g.

higher proportion of unsaturated fatty acids)higher proportion of unsaturated fatty acids) Cold shock proteins Cold shock proteins Metabolic activity relies on psychrophilic enzymesMetabolic activity relies on psychrophilic enzymes

Questions:Questions:

1.1. What the low temperature limits for survival and growth?What the low temperature limits for survival and growth?

2.2. How do individual species adapt genetically to low temperatures?How do individual species adapt genetically to low temperatures?

3.3. Is there commonality between species in adaptation to low Is there commonality between species in adaptation to low temperatures?temperatures?

Test speciesTest species

Halophiles: high salt tolerance oHalobacterium sp. Halobacterium sp. NRC-1NRC-1 – mesophile; genomemesophile; genome sequencedsequencedoHalorubrum lacusprofundiHalorubrum lacusprofundi – psychrotroph from psychrotroph from Deep Lake, Antarctica; draft genome sequenceDeep Lake, Antarctica; draft genome sequence

Methanogens:Methanogens:oMethanosarcina acetivorans –Methanosarcina acetivorans – mesophile; genome mesophile; genome sequencedsequencedoMethanococcoides burtoniiMethanococcoides burtonii – – psychrophile from psychrophile from Ace Lake, Antarctica; draft genome sequencedAce Lake, Antarctica; draft genome sequenced

ControlControloEEscherichia scherichia coli coli – mesophile; genome – mesophile; genome sequencedsequenced

Experimental goalsExperimental goals

Phase I: characterise life’s limitsPhase I: characterise life’s limitso culture individual species at temperatures T~10, 4, culture individual species at temperatures T~10, 4, 0, -40, -4ooCC

o measure growth measure growth

Phase II: characterise genetic changesPhase II: characterise genetic changeso for systems with sequenced genomes, use for systems with sequenced genomes, use microarrays to identify genetic mutationsmicroarrays to identify genetic mutations

o compare species for systematic changes with compare species for systematic changes with decreasing temperaturedecreasing temperature

Microarrays and genetic profilesMicroarrays and genetic profilesMicroarrays detect changes in mRNA (messenger RNA) levelsMicroarrays detect changes in mRNA (messenger RNA) levels DNA DNA mRNA mRNA protein protein Given a sequenced genome, design array of probes that Given a sequenced genome, design array of probes that

react to specific mRNA react to specific mRNA map which proteins are map which proteins are expressed (which genes are active) in a given species & expressed (which genes are active) in a given species & look for variations with changing environmentslook for variations with changing environments

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Signal intensities 42oC (“green channel”)Microarray image

Cold shock\ proteins

Growth curvesGrowth curves

Mesophile: little or no growth at T=0oCPsychrotroph: significant growth at T=0oC lower than previous limit

H. lacusprofundi, psychrotroph: significant growth at T= -1oC lower than previous limit

Morphological cold Morphological cold adaptation?adaptation?

Both Both H. lacusprofundiH. lacusprofundi and and M. burtonii M. burtonii cells are cells are dispersed at moderate dispersed at moderate temperatures, but cluster temperatures, but cluster at low temperatures. This at low temperatures. This effect has also been effect has also been observed in observed in H. H. lacusprofundilacusprofundi at high at high temperatures.temperatures. Why? Ancestral Why? Ancestral memories? memories?

High resolution imagingHigh resolution imaging

Electron microscope imaging ofElectron microscope imaging of Halorubrum lacusprofundiHalorubrum lacusprofundi at T=0at T=0oo C CThread-like structures: transfer of nutrients?Thread-like structures: transfer of nutrients? maintaining structural integrity?maintaining structural integrity? imaging artefact?imaging artefact?

Summary and conclusionsSummary and conclusions Cold environments are commonCold environments are common

o on Earthon Eartho in the Solar systemin the Solar systemo among extrasolar planetary systemssystemsamong extrasolar planetary systemssystems

Life (particularly archaeal life) is abundant in terrestrial cold environments

We are conducting experiments designed to probe the low temperature limits for life and search for systematic genetic adaptation. Preliminary results:

o extended low temperature growth limits for extended low temperature growth limits for H. H. lacusprofundilacusprofundi and and M. burtoniiM. burtonii

o evidence for a significant change in morphology at low evidence for a significant change in morphology at low temperatures temperatures

Some species still prefer mesophilic Some species still prefer mesophilic environments…environments…