Proposed title: Life at High Temperature Chapter no.: _______
Author(s): Brian P. Hedlund
Greg
Fullmer Associate Professor of Life Sciences
School
of Life Sciences, University of Nevada Las Vegas
89154 Las Vegas, NV, USA
Phone:
702-895-0809
Fax:
702-895-3956
E-mail: brian.hedlund@unlv.edu
Jeremy A.
Dodsworth
School
of Life Sciences, University of Nevada Las Vegas
89154 Las Vegas, NV, USA
Phone:
702-895-0809
Fax:
702-895-3956
E-mail:
jeremy.dodsworth@unlv.edu
Chuanlun
Zhang
Department
of Marine Sciences, University of Georgia
166
Marine Sciences Building
Athens,
GA 30602-3636
Phone: (706) 542-3034
FAX Number:
(706) 542-5888
archaea.zhang@gmail.com
Proposed topics
1)
Diversity of high temperature environments.
-
Continental (liquid water and vapor-condensation systems; volcanically active
areas, tectonically driven systems, influence of climate and hydrologic setting,
deep subsurface).
-
Marine (on-axis, off-axis systems). - Other systems (briefly: coal piles,
compost, industrial cooling and heating, subsurface).
2) Definitions,
upper temperature limits of domains, and polyextremophiles.
-
Hyperthermophiles and thermophiles - distinguishing growth from survival. - Upper temperature limits of domains.
-
Polyextremophiles and their habitats - thermoacidophiles, thermophilic
piezophiles.
3)
Diversity of extremely and moderately thermophilic microorganisms: Archaea,
Bacteria, and Eukarya.
- Phylogenetic diversity - transition to
specific thermophilic lineages around 80°C.
- Physiological diversity.
4) Modes
of adaptation of microorganisms to life at high temperature.
- Nucleic acids (positive supercoiling, GC
content in nontranscribed RNAs)
-
Lipids (membrane-spanning lipids, cyclization, ether and ester linkages)
- Proteins
- Adaptations to instability of small
molecules
- Cytoplasm (compatible solutes)
5) Effect
of high temperature on microbial community diversity and structure.
- Increase in temperature leads to loss of
diversity, simplification of communities.
- Quantitative relationships between high
temperature and microbial diversity.
- Loss of diversity translates into loss
of ecosystem functions.
6) Effect
of temperature on ecosystem functioning and biogeochemical cycles.
- Photosynthetic/chemosynthetic transition.
- Carbon cycle. Distinguishing features of
the high temperature cycle.
- Nitrogen cycle. Distinguishing features
of the high temperature cycle.
7) Recent
developments and future directions.
- Impact of genomics approaches (e.g.
“dark matter” lineages)
- Need for more in situ measurements (from
biomarkers to activities)
- Need for more dynamic studies (from
snapshots to movies)
Chapter
Highlights
The
following concepts will be conveyed in this chapter:
1. The
high temperature biome is extensive and diverse. It is inhabited by a
physiologically and phylogenetically diverse group of microorganisms. Above ~80°C the microbial community
is composed entirely of thermophilic phylum- and class-level lineages.
2. A
variety of molecular adaptations to high temperature exist, including
adaptations to protect macromolecules (nucleic acids, lipids, and proteins), to
decrease molecular motion in the cytoplasm, and to address the instability of
small molecules at high temperature.
3. High
temperature leads to a loss of diversity, which leads to loss of ecosystem
function, including a key transition from photosynthetic communities to
chemosynthetic communities. Temperature impacts all biogeochemical cycles in
ways that are currently poorly understood.
4. Current
and future advancements include the discovery of the function of major,
uncultivated lineages, so-called “biological dark matter,” and an increased
focus on the effect of high temperature on ecosystem function.
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