L13W10_MIC105_PhototrophyI

L13W10_MIC105_PhototrophyI - Phototrophy Retinal-based...

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2/5/10 1 Phototrophy • Retinal-based photoheterotrophy in Haloarchaea in some Bacteria • Chlorophyll-based phototrophy only in Bacteria and Eukarya - oxygenic - anoxygenic *
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2/5/10 2 Phototrophy: general principles 1. Photoreceptors are packed in membranes to maximize light absorption 2. Photoreceptors absorb light causing excitation of an electron 3. Photocycle of the receptor is coupled to energy storage *
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2/5/10 3 Retinal-based photoheterotrophy * • in Haloarchaea • in some Bacteria
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2/5/10 4 Haloarchaea ‘Salt loving’ members of the Euryarchaeota
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2/5/10 5 Haloarchaea Require high NaCl concentrations near saturation (Require 1.5 M!, up to 5.2 M; ~7x ocean) Found in hypersaline environments: Great Salt Lake Dead Sea alkaline soda lakes Solar salterns salt-cured meats and fish *
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2/5/10 6 Haloarchaea Red pigmented- C50 carotenoid: bacterioruberin protects cells from light damage *
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2/5/10 7 Haloarchaea Compensate for high external [NaCl] by maintaining high [KCl] internally and synthesize organic molecules to raise internal osmolarity High GC content in DNA (>60%) protects from denaturation at high [salt] Most proteins are acidic, negatively charged on surface, bind K + ions Glycoprotein cell walls containing negatively charged amino acids, stabilized by Na + ions *
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2/5/10 8 Haloarchaea Most are mesophilic Some grow at neutral pH; others are alkaliphiles growing at pH > 9 Most have rigid cells walls made of glycoprotein Contain gas vesicles (rigid hollow protein structures) for buoyancy- float to surface where O 2 is present *
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2/5/10 9 Diverse morphologies * Halobacterium
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2/5/10 10
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2/5/10 11 Haloarchaea Most are organoheterotrophs using proteins or amino acids as carbon and energy sources Most are obligate aerobes; some respire with nitrate as terminal electron acceptor; a few ferment Most obtain supplementary energy using light-driven ion (H + or Cl - ) pumps Rhodopsins capture light energy, and allow generation of proton motive force and ATP *
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2/5/10 12 Proton Motive Force PMF = Δ p = Δψ - 60 Δ pH Transmembrane electrical potential ( Δψ ; charge difference) plus transmembrane pH difference ( Δ pH) *
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2/5/10 13 Proton Motive Force Used as a source of energy to power cell activities ATP synthesis Drives flagellar rotation Powers transport systems *
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2/5/10 14 Light-driven ion pumps Bacteriorhodpsin : pumps protons out Halorhodopsin : pumps Cl - in Both increase proton motive force *
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2/5/10 15 Bacteriorhodopsin Bacteriorhodpsin and halorhodopsin each have seven transmembrane helices and form complexes in the membrane for efficient light absorption Light-driven ion pumps *
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2/5/10 16 Bacteriorhodopsin Each BR or HR contains a molecule of retinal , which absorbs green light and undergoes a conformational change, causing the release of a proton to the outside of the cell.
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