• Phototrophy – Conversion of radiant energy from the sun into

ATP and NADPH

• Autotrophy involves carbon fixation– Conversion of inorganic carbon into organic

molecules

• Photoautotrophy– Involves light rx (energy step)

and dark rx (carbon fixing step)

– Photophosphorylation (light rx) provides ATP and reducing power (NADPH) to power the Calvin-Benson Cycle (dark rx)

• 3 types of phototrophy– Oxygenic phototrophy– Anoxygenic phototrophy– Rhodopsin based phototrophy

• Pathways of oxygenic light reaction– Pair of chlorophyll based photosystems embedded in

membrane• Chloroplast or plasma membrane

Cyclic photophosphorylation produces only ATP

Non-cyclic photophosphorylation produces ATP, NADPH and O2

• Pathways of anoxygenic light reaction– Single bacteriochlorophyll based photosystem – Limited to cyclic photophosphorylation– Use different methods to generate reducing power – Molecules other than water are used as electron donor

– O2 is not produced

• Archaea have no chlorophyll based photosystems• They utilize a membrane protein called

bacteriorhodopsin to capture radiant energy• In oxygen poor environments the pigment functions

as a light-driven proton pump

Dark rx uses ATP and NADPH to fix carbon

Chemolithotrophy

• Inorganic compounds serve as electron donors and energy source

• Common electron donors include – H, reduced N, S or Fe

• Photolithrotrophs require additional energy from sun– Purple bacteria

• Low energy yield so they consume high quantities of inorganic molecules– Significant ecological impact

• Iron bacteria – oxidize ferrous iron (Fe2+) into ferric iron (Fe3+)– Ferrobacillus ferrooxidans

• Nitrifying bacteria – oxidize ammonia (NH3) to nitrate (NO3)

– Nitrosomonas and Nitrobacter

• Hydrogen bacteria – oxidize hydrogen gas (H2) to water (H2O)

– Alcoligenes eutrophus

• Sulfur Oxidizing Bacteria – oxidize sulfides, sulfur and thiosulfate to

sulfuric acid (H2SO4)

– Thiobacillus thiooxidans

• Many chemolithotrophs are autotrophic using CO2 as carbon source

– Use reverse electron flow to reduce NAD

Reverse electron flow is necessary for chemolithoautotrophs to generate reducing power

NADH reduction by sulfide and nitrite

• Chemolithoautotrophy is very inefficient– much of the energy is expended on generating

reducing power rather than ATP

– Many will grow as heterotrophs if supplied with organic carbon sources

• Many can grow either aerobically or anaerobically by varying the final electron acceptor