High pressure and deep
subsurface habitats as
extremes
for many organisms
•  Hydrostatic pressure increases 1 atm with
every 10 m of depth
•  Lithostatic pressure increases 2 atm with
every 10 m of depth
Barophiles (piezophiles) =organisms which live in high pressure
environments. Environments: on oceans floors and deep lakes (hydrostatic
pressures), in subsurface rocks (lithostatic pressures)
Barotolerants - able to survive at high pressures, but can grow in
less extreme environments as well. Usually don't grow at
pressures higher than ~ 500 atm. Obligate barophiles (extreme)- cannot grow (or survive?) outside
of such environments. Barophiles are generally psychrophilic
(below 100m depth the temprature is ~2-3 C)
Barophiles grow in darkness -> are very UV sensitive, lacking
sufficient mechanisms of DNA repair.
Oceans
average depth = 3,800m -> pressure of 380 atm
Maximal depth = 11,000 m -> maximum pressure of 1100
atm
(10 atm = 1 MPa)
Obligate barophiles grow better as pressure
increases. Obligate barophilic bacteria cannot grow at
pressures lower than about 500 atms, but
grow best at about 800 atms. .
E. coli can withstand
high pressures and still
.
retain viability. Under very high pressure E.
coli does not grow well, i.e., the cell
elongates, but cell division is impaired. What happens at high pressures?
High pressure affects cell processes in
similar way to low temperatures.
High pressure decreases volumes and
compresses cell content.
A) Decreased cell membrane fluidity.
B) Decreased binding capacity of enzymes
C) The 3-dimensional structures of DNA
and proteins distort and become
nonfunctional
(D) Motility (bacterial flagellum) is affected
(F) Ribosomes are negatively affected
Adaptation
A1) higher percentages of (poly)unsaturated
fatty acids
A2) the outer membranes of barophiles tend to
have a different protein composition compared
to regular microbes. The porins (diffusion
channels in membranes) of a barophile can be
made up by a specific outer membrane protein
(caused by a specific gene which is switched
on by high pressure).
B) The enzymes of extreme barophiles are
often folded differently, in a way so that the
pressure has less effect on them.
High-pressure genes were found not only in
deep-sea adapted microorganisms, but also in
bacteria growing at atmospheric pressure; so
life emerged from a deep sea environment?
Mariana Trench - the deepest sea
floor at 10,897 m.
In 1996 the Japanese submersible
Kaiko scooped out some mud from
the Mariana trench sea floor and
about180 species of microorganisms
were isolated.
Many were obligate barophiles and
their growth rates were much lower
than those of barotolerant microbes.
amphipod
bacterium
Mariana Trench
Temperatures are incorrect
0.403 in
Deep Subsurface Microbiology
i.e. below the surface of the terrestrial
earth, or below the ocean seafloor
THE DEEP SUBSURFACE BIOSPHERE
• A new field of study, mostly unexplored
Great hoopla at first (in late 1980s & early 90s);
enormous biomass?
• Great difficulties and expense for research:
Drilling through various types of rock to depths of hundreds of
meters (up to 4 km), sometimes below the seafloor (to 110°C).
Who finances the work?
• Questions:
How great a biomass exists?
How much of it is viable and growing?
What types of microorganisms live there?
What is the source of their nutrition and energy?
What influence does the type of rock have?
Are the microbes ancient or frequently introduced?
Could such ecosystems exist on other planets?
Examples of
thermal
gradients
*
E. of Japan
km
W. Colorado
vadose zone
INEL-1
deep borehole,
Idaho
acoustic velocity
temperature
Types of subsurface communities investigated
1-10 km
J = hydrothermal
vent
A = highly permeable sediments, South Carolina
B = saline, low-permeability sedimentary rock, Virginia
C = igneous rocks (granite) and metamorphic rocks, Sweden
D = vadose zone (dry), Columbia Basin, Washington
E = low-permeability sediments, Colorado
F = low-permeability sediments & volcanic tuffs (Nevada test site)
G = fractured basalt, Columbia Basin, Washington
H = sedimentary rock with volcanic intrusions, Mexico
I = low permeability marine sediments, Pacific Ocean
Subsurface subjects to think about:
First, how do you drill through a few kilometers
of rock?
1.
2.
3.
4. 
5. 
6. 
7. 
8. 
How to collect samples without outside contamination
Chemistry of the subsurface crack or pore waters
Origins of the chemical constituents
Chemical reactions occurring in various rocks and sediments
(biological or abiological transformations)
What types of microorganisms are present (identities based on
genetic information and culturing).
How are they making a living in various subsurface habitats?
How great is the biomass, and how rapidly are the microbes
growing or metabolizing?
What combination of extremophilic adaptations are involved?
Barophily/barotolerance?
Thermophily/thermotolerance?
Oligotrophic competence?
Sub-seafloor distribution of prokaryotes near hydrothermal vents
Meters below
seafloor (mbsf)
Examples of deep sub-surface ions and other
compounds: (H2O assumed)
The Usual Suspects
(what origins?)
H2, CH4, H2S or HS–, Fe(II) , Mn(II), NH4+, N2,
NO3–, O2, CO2, HCO3–, SO42-, Fe(III), Mn(IV)
Organic C compounds (origins from surface
recharge or from reactions of some of the above)
What s wrong
with this equation?
Near Pervuvian
Trench, drilling to
Basaltic basement420 mbsf
SO42- from deep brines
& NO3- + O2 from
basaltic aquifers?
6CO2 + 12H2O →
C6H12O6 + 6O2 + 6H2O
DeLong, E.F. (2004)
Science 306: 2198-2200
?????
Pristine
Petroleum or
landfill leachate
methanogenic
SO4reducing
Fe(III)-reducing
The hydrogen (H2) based ecosystem theory for deep
subsurface basalt (Idaho & Nankai Trough)
95% Archaea (mainly thermophilic methanogens)
4 H2 + CO2 → CH4 + 2 H2O [energy]
CO2 → (CH2O)
[cell carbon]
H2 from H2O through the heat of radioactive decay of
uranium (Chapelle et al. 2002)
Or iron in the basalt reduces the H in H2O to H2 gas
Thus, in this particular habitat, autotrophic methanogens
serve as the base of the food chain
However, in most other deep subsurface rocks,
methanogens represent only 3-5% of the microbial
community. (see Newberry et al. 2004-Nankai Trough)
Newberry, C.J. et al. (2004) Environ. Microbiol. 6: 274-287.
E. of Japan
Swedish deep igneous and metamorphic rock sites varying from 100 to 1700 m
Log of
rates-
High
Low
The deep subsurface biomass of Bacteria and
Archaea may (?) exceed the biomass of
that above the surface, but the growth and
metabolic rates
are probably 1/100 to <1/1000 the rates of
microorganisms in surface soils and shallow
aquatic habitats