Purple (Non)Sulfur Bacteria

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Purple (Non)Sulfur Bacteria
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Purple Bacteria

• All are proteobacteria
• Most are facultative aerobes
• Perform aerobic respiration with O2
• Perform photosynthesis without O2
• (there are some species that do aerobic
  photosynthesis)
• Most can use sulfide (S2-) as electron donor
• Some can also use
• sulfur (S0)
• thiosulfate (S2O32-)
• H2
• Organic molecules

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Purple sulfur bacteria

• All are gamma proteobacteria
• Can tolerate high S2-
• Oxidize S2 ? S0 (usually stored intracellularly
  in sulfur granules)
• Later oxidize oxidize S0 ? SO42

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Purple nonsulfur bacteria

• All are alpha or beta proteobacteria
• Cannot tolerate high S2- (1-3 mM)
• Oxidize S2 ? S0 (? SO42)
• Prefer to grow photoheterotrophically(using
  organic molecule as C source)

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Rhodobacter phylogeny

• Proteobacteria
• Class I Alphaproteobacteria
• Order III Rhodobacterales
• Family I Rhodobacteraceae
• Genus I Rhodobacter
• Genus XII Paracoccus

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Rhodobacter characteristics

• Have internal membranes when growing
  photosynthetically
• More when light is lower
• Increases light absorption
• Electron donors for photoautotrophy
• Sulfide (S2-)
• thiosulfate (S2O32-)
• H2

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Rhodobacter characteristics

• Chemotrophic growth
• Aerobic respiration
• Anaerobic conditions
• Alternate respiration (e.g. denitrification)
• Fermentatation
• Can use various C sources
• Formate
• Citrate
• Glycerol
• Ethanol

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Rhodobacter sphaeroides

• Uses BChl a as main pigment
• Carotenes
• spheroidene ( hydroxyspheroidene)
• Converted to corresponding ketocarotenes under
  oxic conditions
• Converts cells from (greenish brown) to red
• Grows slowly photoautotrophically with H2 or S2-
• Prefers photoheterotrophic growth

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Rhodobacter medium

• Per liter
• 0.5 g NaCl
• 0.3 g MgSO47H2O
• 0.5 g (NH4)2SO4
• 0.2 mM CaCl2
• 15 mM KPi (pH 7)
• 1 mL 1000x Chlamy Trace elements
• 1 mL 1000x Vitamins (0.5 g/L thiamineHCl, 1 g/L
  nicotinate, 10 mg/L biotin)
• Autoclave
• Add lactate from sterilized solution to 0.4

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Comparing type 1 and type 2 RCsthe polypeptides
Photosystem I RC proteobacterial RC
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Comparing type 1 and type 2 RCs

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Comparing type 1 and type 2 RCs

H2
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Light-harvesting antenna

• Use a ring of short peptides that bind BChl and
  cartotene as external antenna
• LH1
• ring around the RC
• transfers energy to RC
• LH2
• smaller (independent) rings
• can transfer energy to LH1

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Bacterial photosynthesis

• In order to reduce CO2 (and make carbohydrate),
  it is necessary to have an electron source.
• Anoxygenic photosynthetic bacteria can utilize
  several different electron sources, including H2S
  and Fe2, depending upon the species. (These are
  much easier to oxidize than H2O.)
• Quinone pool is the point of entry. For example,
  the enzyme sulfidequinone oxidoreductase (found
  in several species) catalyzes the reduction of
  quinones using H2S as a reductant H2S Q gt S0
  QH2
• The ways in which bacteria carry out net
  reduction of NADH also differ, depending upon
  their 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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