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