AST 734:Astrobiology Seminar

15 Nov 2004

Lake Vostok, Antarctica:Recent Progress, Future Prospects

David M. KarlOceanography

INTRODUCTION

• Microbial life in extreme and unusual environments• Microbial oceanography, ecology and biogeochemistry• Bacterial physiology and metabolism• Methods development, technology transfer

David M. Karl (dkarl@hawaii.edu, MSB 629)Ph.D. 1978: Biological OceanographyScripps Institution of Oceanography1978-present: UHM / Dept. Oceanography

Research Interests:

OUTLINE

•Microbial life: diversity of habitats and microbes

•Methods for life detection•Life in extreme environments: Antarctica – a

continent of extremes•Lake Vostok – A case study with

extraterrestrial (Mars/Europa) connections

ROLE OF MICROBES INGLOBAL OCEAN ECOLOGY

•Control production and consumption of organic matter

•Control O2 concentration, pH and redox levels•Production and consumption of “greenhouse”

gases (CO2, CH4, N2O)•Control N availability: N2 fixation, nitrification

and denitrification

Microbes make things happen!

DIVERSITY

•Phylogenetic•Metabolic•Habitat/Niche Space

TIME is a critical variable for all three properties

total

marine0

20

40

60

80

100

120

140

160

1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

Year

# B

acte

rial G

enom

es

total

marine

In progress: ~500 total 100-150 marine

Human genome: 3 x 104 genesBacterial genome: 1010 genes

MICROBIAL GENOME SEQUENCING: A “PROGRESS REPORT”

•1st complete genome 1995; by the end of 2004, >300 selected genomes will be available

•30-50% of putative genes have no known function (metabolic regulation/ecology?)

•Horizontal (lateral) gene flow is commonplace so “species” concept is questionable

• Less than 1% of species

• Only 1 “model” system

• Novel microbes and habitats

• Novel physiology/biochemistry

Knowns Unknowns

NOT EVEN THE TIP OF THE ICEBERG!

T. Newberger

THE “STRUGGLE” FOR LIFE

Suppliesenergy

materials

Demandsgrowth

maintenancereproduction

PROGENY

Allocation

Optimalreproductive

tactics

Optimalforagingtactics

OutIn

ORGANISM

RESOURCE

SOURCES OF CARBON, ENERGY AND H/e-

Organic moleculesOrganotrophs

Reduced inorganic moleculesLithotrophs

H/e- Sources

Oxidation of organic or inorganic compoundsChemotrophs

LightPhototrophs

Energy Sources

Reduced, preformed, organic molecules from other organisms

Heterotrophs

CO2 sole or principal biosynthetic carbon sourceAutotrophs

Carbon Sources

150

100

50

0

50-0 1000 2000

DEEPEARTH

HYDROTHERMALVENTS

DEEP SEA

LAKE VOSTOKICE

PRESSURE (bars)

TEM

PE

RA

TUR

E (°

C)

?

?

A. Yayanos

US

DRYVALLEYLAKES

LIFE DETECTION

PAST LIFE- fossils, microfossils,biomarkers, stableisotopes, redoxdiscontinuities- methods: microscopy,GC-MS, chemicaldisequilibria

PRESENT LIFE- viable, metabolically-active or growing cellsunder in situ conditions- methods: microscopy,ATP, LPS, radiorespiro-metry, redox dyes,chemical disequilibria

“FUTURE” LIFE(POTENTIAL)- spores- methods: microscopy,enrichment culture

1986

1998 2001 2002

1993 1994/2004

LESSONS FROM THE PAST

• microbial life at 250?C, and beyond• fossil life forms on Mars

CAUTION ADVISED!

EXTRAORDINARY CLAIMS REQUIRE EXTRAORDINARY EVIDENCE

C. Sagan

Baross & Deming (1983) McKay et al. (1996)

? ?C ?

? ?

? ?

? ?disproven as an

Claimed life at 250on Earth

Claimed “possible”life on Mars

Indirect evidence Indirect evidence

No living organism,ATP or DNA

No living organism,ATP or DNA

Claim subsequentlydisproven as anexperimental artifact

Claim subsequently

interpretation artifact

ANTARCTICA: THE CONTINENT OF EXTREMES

•Hyperoligotrophic seawaters•Cold, dry deserts•Volcanic soils, fumaroles and submarine

hydrothermal vents•Sea ice•Hypersaline and subglacial lakes

“SALEGOS”

Priscu et al. Polar

Geography2003

“SubglacialAntarctic

Lake Exploration

Group of Specialists”

•Lake Vostok is one of ~100 subglacial lakes mapped to date

•Lake Vostok is probably the largest and has become the target for Astrobiology research

•Might be a model for Europa’s ocean

•From Alpine temperate lake to subglaciallake

• Ice cover for ~20 M yrs

Lake VostokChronology

Lake Vostok is a “great” lake

from Bell & Karl (1999, EOS)

LAKE VOSTOK, ANTARCTICA(CIRCA 1996)

•Length 230 km•Width (avg.) 60 km•Depth

–min. <10 m–max. 510 m–avg. 130 m

•Area 14,000 km2

•Volume 1,800 km3

• Ice thickness 3,750-4,200 m

LAKE VOSTOK: CRITICAL HABITAT PARAMETERS

•Temperature•Pressure•Organic/inorganic nutrients•Dissolved gases (and gas hydrates)•Others

•Based on gas content, crystal size, electrical conductivity, isotopic analysis, the authors conclude that theVostok ice core from 3,539 m below the surface of the ice sheet to 3,750 m consists of refrozen Lake Vostok water

Jouzel et al. (1999) Science 286

1998 LAKE VOSTOK SYMPOSIUM

NSF-SPONSORED

•To assess general interest and importance

•Led to accreted ice analysis, excitement and debate

•Glacial ice•Accreted ice

(lake ice)•Liquid lake•Sediments•Rift zone?

Lake Schematic

U.H. ICE CORE ANALYSES

• request/receive Lake Vostok ice core sample from NICL

• 3,602.5-3,603.0 m; 10 cm diameter core, U.S. split

• section (Top/Bottom)

1. Proposal

2. Processing

Archive B T

50 cm

3603.0 3602.5

10 cm

U.S.

LAKE VOSTOK: LESSONS FROM VIKING

•Need for positive and negative controls•Need for redundant assay procedures•Need for a more reliable set of life detection

assays•Need for complementary chemical and

microbiological measurements

Need for careful selection of sampling site(s)

U.H. ICE CORE ANALYSES

•process–bacterial and virus enumeration (epi, SEM/TEM,

flow cytometry)–ATP and LPS–[NO3

- + NO2-], total N

–DOC–radiorespirometry (14C-glucose, 14C-acetate)

ASSAY CONSIDERATIONS

•Sensitivity–ATP can detect ~103 E. coli-sized cells–LPS can detect 1 E. coli-sized cell

•Specificity•False positives

–microscopy ? ALH84001

CROSS ECOSYSTEM COMPARISONS

7.1 ? 2.0<1 ? M164 ? 8.53,600Lake Vostok

60-7040-50

3-52-3

15-2535

5 (summer)5 (winter)

- Palmer-LTER

40-501-235-404,500- N.P. gyre

80-1205-81-55- N.P. gyre

Seawater

DOC(? M)

DON(? M)

[NO3+NO2] (nM)

Depth(m)

Habitat

CROSS ECOSYSTEM COMPARISONS

0.08-0.10<0.53,600Lake Vostok

---125-2502,500- Galapagos Vents

---0.05-0.5237- Ross Ice Shelf (J-9)

250-50010-25

>1,000<20

5 (summer)5 (winter)

- Palmer-LTER

1-20.5-24,500- N.P. gyre

100-25020-505- N.P. gyre

Seawater

LPS (ng/l)ATP (ng/l)Depth (m)Habitat

Direct evidence of microbial life

or contamination?

from Karl et al. (1999)

MICROBIAL ECOSYSTEM MODELS

•Subglacial lake with a hydrothermal system–Oasis of life

•Hyperoligotrophic paleo lake–mostly bio-unavailable C–cryptic growth–monoculture

LAKE VOSTOK SUMMARY

•Accreted ice from 3,603 m in Vostok ice core 5G contains viable microorganisms and reduced organic compounds at low but detectable concentrations

•Lake Vostok penetration and sample return will be required to fully characterize this unique ecosystem and its in situ carbon and energy fluxes

NASA-JPL “Dream” cryobot

discovers hydrothermal vents in Lake

Vostok

•Authors claim low cell density (1 cell/ml)•They also report 16S rRNA genes from obligate

thermophiles• Ice-covered hydrothermal vent?

•McKay et al. (2003) GRL vol. 30–Clathrate formation due to lake water mass

“recycling” by freeze-thaw processes (accreted ice devoid of gas compared to glacial ice)

–Redox state set by O2 content which could be 50 times air saturated value

•Studinger et al. (2004) GRL vol. 31

OTHER RECENT REPORTS

•Aerogravity data used to estimate water depth and basin morphology

•Found 2 separate basins separated by a sill

•New lake volume (5200 km3) increases RT by 300%

Studinger et al. 2004

WHAT DO WE DO NEXT?

•Proceed deliberately, but with great caution to prevent contamination

•Survey Lake Vostok for exploration targets and extant contamination, if any

•Establish “test sites,” e.g. at South Pole, to test drilling technologies, experimental methodologies and ecological hypotheses

•Create and disseminate knowledge

•Recent reports indicate that Russians plan to penetrate the Lake as early as Dec 2004

• International community is trying to enforce a moratorium on drilling (through SCAR)

Nature 430:494 (2004)

•International prospectus for lake entry

•IPY 2007-2008 target

What Next?

Prospectus and Timetable for Lake VostokExploration

Enabling Technologies:

Wants & Needs

SUMMARY

•Antarctica is a continent of extreme habitats•These extreme habitats support the growth of

microbial communities with unusual metabolic strategies and adaptations

•Detailed exploration of microbial life in these extreme/unusual habitats will contribute to general ecological theory and may provide insights to past life on earth and the possibility for extraterrestrial life