metabolic diversity every living being needs: –energy source (inorganic,organic, light) –carbon...
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Metabolic Diversity
• Every living being needs:– Energy source (inorganic,organic, light)– Carbon source (inorganic or organic)
Phototrophy
• Microbial phototrophs:– Anoxygenic
• Purple (non)-sulfur bacteria (proteobacteria)
• Green sulfurs
• Green non-sulfurs
– Oxygenic• Cyanobacteria
• Prochlorophytes
Photosynthetic Pigments
• Chlorophylls– Porphyrins (like cytochromes) with Mg+ – Bacteriochlorophylls a, b, c, d, e, g
• Phycobilins (phycoerythrin, phycocyanin)
• Carotenoids– Hydrophobic– Hydrocarbon chains with conjugated bonds
• Light reaction:– Light energy is conserved as chemical energy
• Dark reaction:– Chemical energy is used to reduce CO2 to
organic compounds
• Reaction center
• Light harvesting (antenna)
Photosynthetic complex in PSB
Oxygenic Photosynthesis
• Involves two distinct photochemical reactions (photosystems I(P700) and II(P680))
• Use light to generate both ATP and NADPH
• Electron transfer in photosystem I produces H+ gradient (also cyclic photophosphorylation)
CO2 Fixation• Calvin cycle requires NAD(P)H and ATP
• Ribulose biphosphate carboxylase (RubisCO)
• Stoichiometry: – 6 CO2 + 12 NADPH + 18 ATP
C6H12O6(PO3H2) + 12 NADP+ + 18 ADP +17 Pi
• Carboxysomes– Polyhedral cell inclusions with crystalline arrays
of RubisCO
Reverse Citric Acid Cycle
• Green sulfur bacteria and green non-sulfur bacteria
• Archaea Sulfolobus and Thermoproteus
• Ferredoxin linked enzymes
Hydroxypropionate Cycle
• Chloroflexus (green non-sulfur)
• 2 CO2 are reduced to glyoxylate
• key intermediate is hydroxypropionate
Chemolithotrophy
• Obtain energy from the oxidation of inorganic compounds
• ATP synthesis is coupled to oxidation of electron donor
• Possible electron donors: H2, sulfide, S0, ammonium, NO2
-, Fe2+
• H2-oxidation catalyzed by hydrogenase, soluble or membrane-bound; most H2-oxidizer are also capable of chemoheterotrophic growth
• Oxidation of reduced Sulfur compounds (H2S, S0, S2O3
-) via SO32-
• Iron oxidation (Fe2+ to Fe3+), anaerobic ferrous iron oxidation by anoxygenic phototrophs (banded iron formation)
Nitrification
• Nitrogen compounds as e--donors: NH3 and NO2
-
• Nitrifiers in soil and water
• Ammonia monooxygenase
• Anammox
Anaerobic Respiration
• Terminal e--acceptors others than O2: Fe3+, NO3
-, fumarate, SO42-, CO2, S0
• Yields less energy than the oxidation of the same compound with O2 would
• Dissimilative metabolism