Chloroflexi

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Chloroflexi
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Chloroflexus aurantiacus

• Filamentous gliding phototroph
• Thermophilic (50-60 C)
• higher temperatures than any other anoxygenic
  phototroph
• Forms massive accumulations as mats in neutral to
  alkaline hot springs
• usually found as lower layer of microbial
  mat,with cyanobacteria growing in layers above
  it
• may be found alone in springs high in sulfide

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Chloroflexus aurantiacus

• Grows primarily as a photoheterotroph
• Electron donors
• organic products of cyanobacteria
• hydrogen
• sulfide
• The CO2 fixation mechanism
• lack ribulose bisphosphate carboxylase activity
• 3-hydroxypropionate pathway
• unique among all phototrophs
• The light-harvesting apparatus chlorosomes
• like green sulfur bacteria, but smaller
• Reaction center type 2
• like purple bacteria, but with one BChl replaced
  by BPhe
• lack internal membranes typical of the purple
  bacteria.

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Types of (Bacterio)Chlorophyll
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Chlorosomes

• Big bags of lipid pigment
• BChl c, d, e (a little BChl a is attached)
• Carotenes
• Lipids glycolipids, phospholipids, wax esters
• Very little protein (10 different polypeptides,
  not required for spectral properties)
• Seem to self-assemble
• Not a lipid bilayer
• Very fast efficient energy transfer
• A single chlorosome may be attached to as many as
  100 reaction centers.

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Chlorosome model (Chlorobium)
Don Bryant
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Alfred Holzwarth
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Bacterial photosynthesis

• Except for the cyanobacteria, all other
  photosynthetic bacteria are anoxygenic (they do
  not produce oxygen).
• They contain a reaction center of either type 1
  or type 2 and a cytochrome bc complex.
• With this arrangement, they are able to perform
  cyclic electron flow to produce a H
  electrochemical gradient.
• This is sufficient to produce ATP, but there is
  no net reduction of NAD(P)H.
• The ways in which the 2 types of organisms carry
  out cyclic electron flow are different, depending
  upon the type of reaction center (RC).

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Bacterial photosynthesis

• Type 2 RC
• reduces the mobile quinone
• Quinol is oxidized by cyt bc
• Electrons passed to cyt c
• cyt c re-reduces the primary donor of the RC

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Bacterial photosynthesis

• Type 1 RC
• RC reduces ferredoxin
• FdNAD oxidoreductase (FNR) passes electrons to
  NAD
• Type 2 RC
• also contain a NADHquinone oxidoreductase
  (a.k.a. NADH dehydrogenase).
• Oxidation of quinones drives proton pumping.
• When the proton gradient gets large enough, the
  reverse reaction becomes favorable with
  dissipation of the proton gradient.

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Comparing type 1 and type 2 RCs

BPhe
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Comparing type 1 and type 2 RCs

BPhe
H2
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