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Metabolic Diversity
• Every living being needs:
– Energy source (inorganic,organic, light)
– Carbon source (inorganic or organic)
• 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
• Use light to generate both ATP and NADPH
• Electron transfer in photosystem I produces
H+ gradient (also cyclic
CO2 Fixation
• Calvin cycle requires NAD(P)H and ATP
• Ribulose biphosphate carboxylase
• 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
• Archaea Sulfolobus and Thermoproteus
• Ferredoxin linked enzymes
Hydroxypropionate Cycle
• Chloroflexus (green non-sulfur)
• 2 CO2 are reduced to glyoxylate
• key intermediate is hydroxypropionate
• 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 H2oxidizer 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)
• 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