Transcript Thiobacillus thiooxidans

• 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