THEME 7(2)

• Anoxygenic PHOTOTROPHIC (Purple sulphur).
• Purple sulfur

  Genera: Chromatium, Thermochromatium

  • use Hydrogen sulfide (H2S) as e- donor for photosynthesis.
  • found in anoxic zones where H2S is found (lakes, marine sediments)
  • members in Gammaproteobacteria
  • purple colour from carotenoids (accessory pigment to harvest light)
  • use Q-type photosystem and fix carbon in Calvin cycle.
• Autotrophic growth

  • H2S oxidised to elemental sulfur (S) deposited as granules
  • S oxidised to sulfate as an e- donor for photosynthesis
  • some store S0 in periplasm (and have vesicular intracellular photosynthetic membrane systems) .
  • some deposit S0 outside cells and have lamellar intracellular photosynthetic membrane systems - many use other reduced sulfur compounds (thiosulphate).
• Purple NON-sulfur:

  Genera: Rhodospirillum, Rhodoferax, Rhodopseudomoas, Rhodobacteria

  • most metabolically diverse - wide range of C sources and e- donors (aa, organic acids, alcohols, sugars)
  • synthesize a range of carotenoids giving them colours (purple, red, orange).
• Purple NON-sulfur:
• Purple NON-sulfur:

  • use VER LOW levels of H2S
  • Photoheterotrophs (light energy source)
  • use Q-type photosystem and bacteriochlorophyll
  • morphologically and phylogenetically diverse (Alpha proteobacteria and Betaproteobacteria)
  • aerobic anoxygenic phototrophs – Roseobacter, Erythrobacter
• Green sulfur

  Genera: Chlorobium, Chlorobaculum, Prosthecochloris

  Phylum: Chlorobi

  contain bacteriochlorophyll in chlorosomes in cell periphery

  chlorosomes = light harvesting organelles -allow bacteria to grow at high light intensity.
• Green sulfur: the chlorosomes

  • allow bacteria to grow at high light intensity
  • green and brown - little metabolic versatility: typically nonmotile, anaerobic anoxygenic phototrophs
  • oxidise H2S TO S0 and SO4 2- for autotrophy - S0 produced from oxidation is deposited outside cell.
• Consortia Consortium:

  • intimate 2-membered association
  • involves green sulphur bacterium (epibiont) attached to chemoorganotroph
  • Chlorochromatium aggregatum (mixed green culture)
• Filamentous anoxygenic phototrophs

  Phylum: Chloroflexi

  Genera: Chloroflexus, Heliothrix, Roseiflexus

  • metabolically diverse (aerobic and anaerobic chemoorganootrophs)
  • most uncultivated and uncharacterised