title: Contribution of a sodium ion gradient to energy conservation during fermentation in the cyanobacterium Arthrospira (Spirulina) maxima CS-328.
abstract: Sodium gradients in cyanobacteria play an important role in energy storage under photoautotrophic conditions but have not been well studied during autofermentative metabolism under the dark, anoxic conditions widely used to produce precursors to fuels. Here we demonstrate significant stress-induced acceleration of autofermentation of photosynthetically generated carbohydrates (glycogen and sugars) to form excreted organic acids, alcohols, and hydrogen gas by the halophilic, alkalophilic cyanobacterium Arthrospira (Spirulina) maxima CS-328. When suspended in potassium versus sodium phosphate buffers at the start of autofermentation to remove the sodium ion gradient, photoautotrophically grown cells catabolized more intracellular carbohydrates while producing 67% higher yields of hydrogen, acetate, and ethanol (and significant amounts of lactate) as fermentative products. A comparable acceleration of fermentative carbohydrate catabolism occurred upon dissipating the sodium gradient via addition of the sodium-channel blocker quinidine or the sodium-ionophore monensin but not upon dissipating the proton gradient with the proton-ionophore dinitrophenol (DNP). The data demonstrate that intracellular energy is stored via a sodium gradient during autofermentative metabolism and that, when this gradient is blocked, the blockage is compensated by increased energy conversion via carbohydrate catabolism.
authors: Princeton University, Department of Chemistry and Princeton Environmental Institute, Princeton, New Jersey, USA.
authors: Damian
authors: D
authors: Carrieri
authors: Gennady
authors: G
authors: Ananyev
authors: Oliver
authors: O
authors: Lenz
authors: Donald A
authors: DA
authors: Bryant
authors: G Charles
authors: GC
authors: Dismukes
mesh_terms: D000438:Alcohols / Q000378:metabolism; D052818:Autotrophic Processes; D050260:Carbohydrate Metabolism; D002264:Carboxylic Acids / Q000378:metabolism; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004734:Energy Metabolism; D005285:Fermentation; D006859:Hydrogen / Q000378:metabolism; D007477:Ions / Q000378:metabolism; D008969:Molecular Sequence Data; D052817:Phototrophic Processes; D011188:Potassium / Q000378:metabolism; D017422:Sequence Analysis, DNA; D012964:Sodium / Q000378:metabolism*; D053545:Spirulina / Q000378:metabolism*
chemical_list: D000438:Alcohols; D002264:Carboxylic Acids; D004269:DNA, Bacterial; D007477:Ions; D006859:Hydrogen; D012964:Sodium; D011188:Potassium