to the classic Calvin-Benson cycle, at least five additional
pathways are known (Hügler and Sievert, 2011; Figure 1).
Future directions
Chemosynthesis affects the chemical environment in fluid
and rocks. How microbes mediate mineral transformations is a major field of biogeochemical research
(Holden et al., 2012). Deep in the subseafloor, the minerals olivine and pyroxene react with water releasing
hydrogen in a process called serpentinization. The potential for life in these zones is reflected in uplifted ophiolites
where microbes are recorded; the metabolic pathways and
consequences of the alkaline habitat are far from understood (Schrenk et al., 2013). Measurement of production
rates in most marine-reducing habitats is difficult and
especially challenging at hydrothermal vents where strong
chemical gradients exist. The degree to which microorganisms are interdependent within a community that
adapts a variety of metabolisms to changing chemical conditions is unclear (Sievert and Vetriani, 2012) and suggests
that studies need to address the entire metabolome of
a chemoautotrophic setting. More accessible are openocean hypoxic zones where the complexity of microbial
interactions in a cascade of redox reactions is revealed
by new genomic approaches. The development of modeling tools (e.g., Amend et al., 2011) to assess bioenergetics
of redox/synthesis reactions can help formulate testable
ideas of metabolic and microbial diversity in many settings. Relationships of these microbes with eukaryotes
and metazoans are complex, often supporting communities with the highest natural biomass of the ocean. Symbiotic associations continue to contribute information on
cell-cell signaling and evolutionary patterns. Exploration
of deep-sea chemosynthetic habitats has led to many fundamental discoveries in basic life processes and redirected
our considerations of the origin of life and life beyond
Earth. The potential remains to discover energy sources
not linked to processes on or above the seafloor. Exploration, both on the seafloor and in laboratories, continues to
challenge our concepts of basic life processes.
Bibliography
Amend, J. P., McCollom, T. M., Hentscher, M., and Bach, W., 2011.
Catabolic and anabolic energy for chemolithoautotrophs in deepsea hydrothermal systems hosted in different rock types.
Geochimica et Cosmochimica Acta, 75, 5736–5748.
Edwards, K. J., Bach, W., and McCollom, T. M., 2005.
Geomicrobiology in oceanography: microbe–mineral interactions at and below the seafloor. Trends in Microbiology, 13,
449–456.
Helm, K. P., Bindoff, N. L., and Church, J. A., 2011. Observed
decreases in oxygen content of the global ocean. Geophysical
Research Letters, 38, L23602.
Holden, J. F., Breier, J. A., Rogers, K. L., Schulte, M. D., and Toner,
B. M., 2012. Biogeochemical processes at hydrothermal vents:
microbes and minerals, bioenergetics, and carbon fluxes. Oceanography, 25, 196–208.
Hügler, M., and Sievert, S. M., 2011. Beyond the Calvin Cycle:
autotrophic carbon fixation in the ocean. Annual Review of
Marine Science, 3, 261–289.
Jørgensen, B. B., and Boetius, A., 2007. Feast and famine – microbial life in the deep-sea bed. Nature Reviews Microbiology, 5,
770–781.
Kormas, K. A., Tivey, M. K., Von Damm, K., and Teske, A., 2006.
Bacterial and archaeal phylotypes associated with distinct mineralogical layers of a white smoker spire from a deep-sea hydrothermal vent site (9
N, East Pacific Rise). Environmental
Microbiology, 8, 909–920.
Levin, L. A., 2005. Ecology of cold seep sediments: interactions of
fauna with flow, chemistry and microbes. Oceanography and
Marine Biology: An Annual Review, 43, 1–46.
Martin, W., and Russell, M. J., 2003. On the origins of cells:
a hypothesis for the evolutionary transitions from abiotic geochemistry to chemoautotrophic prokaryotes, and from prokaryotes to nucleated cells. Philosophical Transactions of the Royal
Society of London, Series B: Biological Sciences, 358, 59–83.
McCollom, T. M., and Shock, E. L., 1997. Geochemical constraints
on chemolithoautotrophic metabolism by microorganisms in
seafloor hydrothermal systems. Geochimica et Cosmochimica
Acta, 61, 4375–4392.
Schrenk, M. O., Brazelton, W. J., and Lang, S. Q., 2013. Serpentinization, carbon, and deep life. Reviews in Mineralogy and Geochemistry, 75, 575–606.
Sievert, S. M., and Vetriani, C., 2012. Chemoautotrophy at deep-sea
vents: past, present, and future. Oceanography, 25, 218–233.
Smith, C. R., and Baco, A. R., 2003. Ecology of whale falls at the
deep-sea floor. Oceanography and Marine Biology: An Annual
Review, 41, 311–354.
Sylvan, J. B., Toner, B. M., and Edwards, K. J., 2012. Life and death
of deep-sea vents: bacterial diversity and ecosystem succession
on inactive hydrothermal sulfides. MBio, 3, e00279-11,
doi:10.1128/mBio.00279-11.
Tunnicliffe, V., Juniper, S. K., and Sibuet, M., 2003. Reducing environments of the deep-sea floor. In Tyler, P. A. (ed.), Ecosystems
of the World: The Deep-Sea. Amsterdam: Elsevier Press,
pp. 81–110. Ch. 4.
Wright, J. J., Konwar, K. M., and Hallam, S. J., 2012. Microbial
ecology of expanding oxygen minimum zones. Nature Reviews
Microbiology, 10, 381–394.
Cross-references
Anoxic Oceans
Black and White Smokers
Deep Biosphere
Hydrothermalism
Ocean Acidification
CLAY MINERALS
Rüdiger Stein
Alfred Wegener Institute, Helmholtz Centre for Polar and
Marine Research (AWI), Bremerhaven, Germany
Definition
Clay minerals are hydrous aluminum phyllosilicates. The
main representatives are kaolinite, illite, chlorite, and
smectite.
CLAY MINERALS
87
pathways are known (Hügler and Sievert, 2011; Figure 1).
Future directions
Chemosynthesis affects the chemical environment in fluid
and rocks. How microbes mediate mineral transformations is a major field of biogeochemical research
(Holden et al., 2012). Deep in the subseafloor, the minerals olivine and pyroxene react with water releasing
hydrogen in a process called serpentinization. The potential for life in these zones is reflected in uplifted ophiolites
where microbes are recorded; the metabolic pathways and
consequences of the alkaline habitat are far from understood (Schrenk et al., 2013). Measurement of production
rates in most marine-reducing habitats is difficult and
especially challenging at hydrothermal vents where strong
chemical gradients exist. The degree to which microorganisms are interdependent within a community that
adapts a variety of metabolisms to changing chemical conditions is unclear (Sievert and Vetriani, 2012) and suggests
that studies need to address the entire metabolome of
a chemoautotrophic setting. More accessible are openocean hypoxic zones where the complexity of microbial
interactions in a cascade of redox reactions is revealed
by new genomic approaches. The development of modeling tools (e.g., Amend et al., 2011) to assess bioenergetics
of redox/synthesis reactions can help formulate testable
ideas of metabolic and microbial diversity in many settings. Relationships of these microbes with eukaryotes
and metazoans are complex, often supporting communities with the highest natural biomass of the ocean. Symbiotic associations continue to contribute information on
cell-cell signaling and evolutionary patterns. Exploration
of deep-sea chemosynthetic habitats has led to many fundamental discoveries in basic life processes and redirected
our considerations of the origin of life and life beyond
Earth. The potential remains to discover energy sources
not linked to processes on or above the seafloor. Exploration, both on the seafloor and in laboratories, continues to
challenge our concepts of basic life processes.
Bibliography
Amend, J. P., McCollom, T. M., Hentscher, M., and Bach, W., 2011.
Catabolic and anabolic energy for chemolithoautotrophs in deepsea hydrothermal systems hosted in different rock types.
Geochimica et Cosmochimica Acta, 75, 5736–5748.
Edwards, K. J., Bach, W., and McCollom, T. M., 2005.
Geomicrobiology in oceanography: microbe–mineral interactions at and below the seafloor. Trends in Microbiology, 13,
449–456.
Helm, K. P., Bindoff, N. L., and Church, J. A., 2011. Observed
decreases in oxygen content of the global ocean. Geophysical
Research Letters, 38, L23602.
Holden, J. F., Breier, J. A., Rogers, K. L., Schulte, M. D., and Toner,
B. M., 2012. Biogeochemical processes at hydrothermal vents:
microbes and minerals, bioenergetics, and carbon fluxes. Oceanography, 25, 196–208.
Hügler, M., and Sievert, S. M., 2011. Beyond the Calvin Cycle:
autotrophic carbon fixation in the ocean. Annual Review of
Marine Science, 3, 261–289.
Jørgensen, B. B., and Boetius, A., 2007. Feast and famine – microbial life in the deep-sea bed. Nature Reviews Microbiology, 5,
770–781.
Kormas, K. A., Tivey, M. K., Von Damm, K., and Teske, A., 2006.
Bacterial and archaeal phylotypes associated with distinct mineralogical layers of a white smoker spire from a deep-sea hydrothermal vent site (9
N, East Pacific Rise). Environmental
Microbiology, 8, 909–920.
Levin, L. A., 2005. Ecology of cold seep sediments: interactions of
fauna with flow, chemistry and microbes. Oceanography and
Marine Biology: An Annual Review, 43, 1–46.
Martin, W., and Russell, M. J., 2003. On the origins of cells:
a hypothesis for the evolutionary transitions from abiotic geochemistry to chemoautotrophic prokaryotes, and from prokaryotes to nucleated cells. Philosophical Transactions of the Royal
Society of London, Series B: Biological Sciences, 358, 59–83.
McCollom, T. M., and Shock, E. L., 1997. Geochemical constraints
on chemolithoautotrophic metabolism by microorganisms in
seafloor hydrothermal systems. Geochimica et Cosmochimica
Acta, 61, 4375–4392.
Schrenk, M. O., Brazelton, W. J., and Lang, S. Q., 2013. Serpentinization, carbon, and deep life. Reviews in Mineralogy and Geochemistry, 75, 575–606.
Sievert, S. M., and Vetriani, C., 2012. Chemoautotrophy at deep-sea
vents: past, present, and future. Oceanography, 25, 218–233.
Smith, C. R., and Baco, A. R., 2003. Ecology of whale falls at the
deep-sea floor. Oceanography and Marine Biology: An Annual
Review, 41, 311–354.
Sylvan, J. B., Toner, B. M., and Edwards, K. J., 2012. Life and death
of deep-sea vents: bacterial diversity and ecosystem succession
on inactive hydrothermal sulfides. MBio, 3, e00279-11,
doi:10.1128/mBio.00279-11.
Tunnicliffe, V., Juniper, S. K., and Sibuet, M., 2003. Reducing environments of the deep-sea floor. In Tyler, P. A. (ed.), Ecosystems
of the World: The Deep-Sea. Amsterdam: Elsevier Press,
pp. 81–110. Ch. 4.
Wright, J. J., Konwar, K. M., and Hallam, S. J., 2012. Microbial
ecology of expanding oxygen minimum zones. Nature Reviews
Microbiology, 10, 381–394.
Cross-references
Anoxic Oceans
Black and White Smokers
Deep Biosphere
Hydrothermalism
Ocean Acidification
CLAY MINERALS
Rüdiger Stein
Alfred Wegener Institute, Helmholtz Centre for Polar and
Marine Research (AWI), Bremerhaven, Germany
Definition
Clay minerals are hydrous aluminum phyllosilicates. The
main representatives are kaolinite, illite, chlorite, and
smectite.
CLAY MINERALS
87