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4. Microbial paleontology
4.1 Origin of life-molecules and life-styles
- 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.
- Possible syntheses of sugars, purines, pyrimidines and amino acids.
- Initial reaction mechanisms: a) "warm (hot) soup metabolism" in the cytoplasm.
- Initial reaction mechanisms: b) in the cold on chemically reactive solid surfaces.
- The role of mineral surfaces in the evolution of biochemistry: e.g.
ironsulfides, clays.
- Nutrient scavenging and retention in dilute environments.
- Initial topologies needed for metabolism: membrane associated electron transport and charge (proton) translocation.
- Initial physiologies: fermentation, CO2-reduction to CH4,
Fe(II+)-oxidation by photosynthesis, mechanisms for assimilative CO2-fixation.
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, 700nm to 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); Chloroflexus spp. (diderm, but actually gram+); Cyanobacteria
(some are gram +); Chlorobium spp.; phototrophic Proteobacteria.
- Did ferrotrophic photosynthesis emerge before or after organotrophic
photosynthesis ?
- Energetic prerequisites and advantages of chlorophyll-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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