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4. Microbial paleontology
4.1 Origin of lifestyles
- Theories about the chemolithoautotrophic
origin of life and possible lifestyles of
ancient microbes.
- Theories about the chemoorganotrophic origin
of life: organic molecules in the "primordial
soup" and remineralization of organics from
early biomass.
- Hydrothermal synthesis of amino acids,
purines and pyrimidines.
- Initial mechanisms: a) "soup metabolism" in
the cytoplasm, b) topologies for metabolism:
membrane associated electron transport, proton
translocation.
- Initial physiologies: fermentation,
CO2-reduction to CH4, Fe(II+)-oxidation by
photosynthesis, mechanisms for assimilative
CO2-fixation.
- The role of mineral surfaces in the
evolution of biochemistry: e.g. ironsulfides,
clays.
4.2 From RNA to RNA/protein to
DNA/RNA/protein worlds.
- Early catalytic molecules, catalytic
RNA.
- Evolution of bio-cryptography.
- Life was originally prokaryotic and
anaerobic.
- How "primitive" prokaryotes shaped 3.5
billion years of evolution.
- Enzyme evolution: metabolism(s) in
non-compartmentalized prokaryotic cells.
- Evolutionarily missing microbial ecosystem
processes.
4.3 Evolution of communities
- Evolution in the absence of other organisms:
exploitation of energy and chemicals.
- The necessity for redox cycling of the
nutritive elements: development of specialist
microbes.
- Exploitable sources of electrons, oxidants
and energy.
- The emergence of communities able to do very
different things.
- The missing prokaryote that can do
everything.
- Ancestral communities were nearly
omnipotent: sulfur-, ferric-iron-,
sulfate-respiration preceeding fermentation,
methanogenesis and photosynthesis.
- Initially abundant electron acceptors: CO2,
Fe(III+), S0 (present in traces SO42-, NO3-,
O2).
- Initially abundant electron donors: reduced
inorganic (and organic ?) compounds in
hydrothermal fluids: H2, H2S, Fe(II+), Corg.
favouring thermophilic chemolithotrophs.
4.4 Evolution from chemotrophic to
phototrophic ways of life
- Methanogenesis might have preceeded
photosynthesis. Was early photoynthesis
recycling methane ?
- Prerequisites for using the energy of
sunlight: pigment and protein complexes (light
harvesting, reaction centers for near
IR-radiation, 700 &endash;1100nm); exploitation
of electron sources and aquisition of
C-assimilation mechanism.
- How old are the photosystems and when and
from where did photosystem II emerge ?
- Possible evolutionary sequence among the
phototrophs: Heliobacterium spp. (gram+, low
G+C) ý Chloroflexus spp. (diderm, but
actually gram+) ý Cyanobacteria (some are
gram +) ý Chlorobium spp. ý
phototrophic Proteobacteria.
- Did ferrotrophic photosynthesis emerge
before or after organotrophic photosynthesis
?
- Energetic prerequisites and advantages of
chl-a-based oxic photosynthesis and of using
H2O-electrons.
- Developing UV-radiation protection;
"sunscreen pigments".
- Developing protection against oxygen
poisoning: superoxide dismutases.
- Coping with the chemistry of iron in an oxic
world: iron aquisition, siderophores,
iron-containing proteins.
- Fundamental metabolic adaptations during the
anoxic to oxic transition.
4.5 Sedimentary records of biogeochemical
processes
- Microbial metabolites (activities) which are
preserved in rocks.
- Life's geochemical and geophysical
signatures: molecular fossils, biomarkers,
hopanoids (bacteria), sterenes (eukarya),
polyisokenoates (Archaea), kerogens, black
shales, bio-minerals, BIF, sedimentary deposits,
precambrian stromatolites, isotope
fractionation.
4.6 The rock record vs. the genome record of
microbial evolution.
- Evolutionary theory with microbial genomes:
molecular history with genome sequence
information.
- How old is the prokaryotic genome ?
- Genetic approaches to reconstruct
geochemical processes.
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