AST 734: Astrobiology Seminar 15 Nov 2004

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AST 734Astrobiology Seminar15 Nov 2004

• Lake Vostok, Antarctica
• Recent Progress, Future Prospects

David M. Karl Oceanography
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INTRODUCTION
David M. Karl (dkarl_at_hawaii.edu, MSB 629) Ph.D.
1978 Biological Oceanography Scripps
Institution of Oceanography 1978-present UHM /
Dept. Oceanography Research Interests

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

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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

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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!

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DIVERSITY

• Phylogenetic
• Metabolic
• Habitat/Niche Space

TIME is a critical variable for all three
properties
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In progress 500 total
100-150 marine
total
total
Human genome 3 x 104 genes Bacterial genome
1010 genes
marine
marine
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MICROBIAL GENOME SEQUENCING A PROGRESS REPORT

• 1st complete genome 1995 by the end of 2004,
  gt300 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

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NOT EVEN THE TIP OF THE ICEBERG!
T. Newberger
Knowns
Unknowns

• Less than 1 of species
• Only 1 model system

• Novel microbes and habitats
• Novel physiology/ biochemistry

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THE STRUGGLE FOR LIFE
ORGANISM
Supplies energy materials
Demands growth maintenance reproduction
Allocation
Out
In
RESOURCE
PROGENY
Optimal reproductive tactics
Optimal foraging tactics
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SOURCES OF CARBON, ENERGY AND H/e-
Carbon Sources
Autotrophs CO2 sole or principal biosynthetic carbon source
Heterotrophs Reduced, preformed, organic molecules from other organisms
Energy Sources
Phototrophs Light
Chemotrophs Oxidation of organic or inorganic compounds
H/e- Sources
Lithotrophs Reduced inorganic molecules
Organotrophs Organic molecules
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150
?
DEEP
EARTH
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TEMPERATURE (C)
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HYDROTHERMAL
VENTS
?
US
DEEP SEA
0
LAKE VOSTOK
ICE
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-
0
1000
2000
PRESSURE (bars)
A. Yayanos
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LIFE DETECTION
FUTURE LIFE (POTENTIAL) - spores - methods
microscopy, enrichment culture
PRESENT LIFE - viable, metabolically- active or
growing cells under in situ conditions - methods
microscopy, ATP, LPS, radiorespiro- metry, redox
dyes, chemical disequilibria
PAST LIFE - fossils, microfossils, biomarkers,
stable isotopes, redox discontinuities - methods
microscopy, GC-MS, chemical disequilibria
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1993
1994/2004
1986
1998
2001
2002
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LESSONS FROM THE PAST
CAUTION ADVISED!

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

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EXTRAORDINARY CLAIMS REQUIRE EXTRAORDINARY
EVIDENCE
C. Sagan
Baross Deming (1983)
McKay et al. (1996)



C






disproven as an
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ANTARCTICA THE CONTINENT OF EXTREMES

• Hyperoligotrophic seawaters
• Cold, dry deserts
• Volcanic soils, fumaroles and submarine
  hydrothermal vents
• Sea ice
• Hypersaline and subglacial lakes

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SALEGOS
Priscu et al. Polar Geography 2003 Subglacial
Antarctic Lake Exploration Group of Specialists
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• 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 Europas ocean

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Lake Vostok Chronology

• From Alpine temperate lake to subglacial lake
• Ice cover for 20 M yrs

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Lake Vostok is a great lake
from Bell Karl (1999, EOS)
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LAKE VOSTOK, ANTARCTICA(CIRCA 1996)

• Length 230 km
• Width (avg.) 60 km
• Depth
• min. lt10 m
• max. 510 m
• avg. 130 m
• Area 14,000 km2
• Volume 1,800 km3
• Ice thickness 3,750-4,200 m

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LAKE VOSTOK CRITICAL HABITAT PARAMETERS

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

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• 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
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1998 LAKE VOSTOK SYMPOSIUMNSF-SPONSORED

• To assess general interest and importance
• Led to accreted ice analysis, excitement and
  debate

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Lake Schematic

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

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U.H. ICE CORE ANALYSES
1. Proposal

• request/receive Lake Vostok ice core sample from
  NICL
• 3,602.5-3,603.0 m 10 cm diameter core, U.S. split

2. Processing

• section (Top/Bottom)

10 cm
50 cm
Archive
T
B
3603.0
3602.5
U.S.
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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)

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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)

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ASSAY CONSIDERATIONS

• Sensitivity
• ATP can detect 103 E. coli-sized cells
• LPS can detect 1 E. coli-sized cell
• Specificity
• False positives
• microscopy ? ALH84001

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CROSS ECOSYSTEM COMPARISONS
Habitat Depth (m) NO3NO2 (nM) DON (?M) DOC (?M)
Seawater
- N.P. gyre 5 1-5 5-8 80-120
- N.P. gyre 4,500 35-40 1-2 40-50
- Palmer-LTER 5 (summer) 5 (winter) 15-25 35 3-5 2-3 60-70 40-50
Lake Vostok 3,600 164 ? 8.5 lt1 ?M 7.1 ? 2.0
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CROSS ECOSYSTEM COMPARISONS
Habitat Depth (m) ATP (ng/l) LPS (ng/l)
Seawater
- N.P. gyre 5 20-50 100-250
- N.P. gyre 4,500 0.5-2 1-2
- Palmer-LTER 5 (summer) 5 (winter) gt1,000 lt20 250-500 10-25
- Ross Ice Shelf (J-9) 237 0.05-0.5 ---
- Galapagos Vents 2,500 125-250 ---
Lake Vostok 3,600 lt0.5 0.08-0.10
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Direct evidence of microbial life or
contamination?
from Karl et al. (1999)
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MICROBIAL ECOSYSTEM MODELS

• Subglacial lake with a hydrothermal system
• Oasis of life
• Hyperoligotrophic paleo lake
• mostly bio-unavailable C
• cryptic growth
• monoculture

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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

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NASA-JPL Dream cryobot discovers hydrothermal
vents in Lake Vostok
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• Authors claim low cell density (1 cell/ml)
• They also report 16S rRNA genes from obligate
  thermophiles
• Ice-covered hydrothermal vent?

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OTHER RECENT REPORTS

• 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

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• 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
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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

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• 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 430494 (2004)
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What Next?

• International prospectus for lake entry
• IPY 2007-2008 target

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Prospectus and Timetable for Lake Vostok
Exploration
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Enabling Technologies Wants Needs
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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

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