• 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