Abstract

To redirect NAD(P)H consumed by dehydrogenases to NiFe-hydrogenase, the genes encoding for lactate dehydrogenase (ddh) and alcohol dehydrogenase (adh) were disrupted in a glucose tolerant mutant of unicellular cyanobacterium Synechocystis sp. strain PCC6803 (GT strain). The cells of GT strain, ddh deficient (Dddh) mutant and both adh and ddh deficient (DadhDddh) mutant were harvested at the late-logarithmic growth phase of photoautotrophic culture in antibiotic-free BG-11 medium. Dark anaerobic hydrogen production in GT strain, Dddh mutant and DadhDddh mutant in nitrate-free HEPES buffer solution without or with glucose has been studied by following the time courses of the number of moles of hydrogen, endogenous and exogenous glucose, lactate, acetate and ethanol per culture volume and the dry cell weight concentration. Dark incubation of cells of Dddh mutant and DadhDddh mutant in HEPES buffer solution without glucose resulted 1.16-fold and 1.15-fold increases in the initial hydrogen production rates over GT strain, respectively, while 1.1-fold and 0.85-fold increases in the number of moles of hydrogen per culture volume at 96 h over GT strain, respectively. When hydrogen production experiments were performed in the glucose-added HEPES buffer solution, dark incubation of cells of Dddh mutant and DadhDddh mutant resulted 1.4-fold and 1.6-fold increases in the initial hydrogen production rates over GT strain without glucose run, respectively, while 1.5-fold and 1.3-fold increases in the number of moles of hydrogen per culture volume at 96 h over GT strain without glucose run, respectively.

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