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Effect of trace metals on ethanol production from synthesis gas by the ethanologenic acetogen, <Emphasis Type="Italic">Clostridium</Emphasis><Emphasis Type="Italic">ragsdalei</Emphasis>
Authors:Jyotisna Saxena  Ralph S Tanner
Institution:(1) Department of Botany and Microbiology, University of Oklahoma, Norman, OK 73019, USA;(2) Coskata, Inc., 4575 Weaver Parkway, Suite 100, Warrenville, IL 60555, USA
Abstract:The effect of trace metal ions (Co2+, Cu2+, Fe2+, Mn2+, Mo6+, Ni2+, Zn2+, SeO4 and WO4 ) on growth and ethanol production by an ethanologenic acetogen, Clostridium ragsdalei was investigated in CO:CO2-grown cells. A standard acetogen medium (ATCC medium no. 1754) was manipulated by varying the concentrations of trace metals in the media. Increasing the individual concentrations of Ni2+, Zn2+, SeO4 and WO4 from 0.84, 6.96, 1.06, and 0.68 μM in the standard trace metals solution to 8.4, 34.8, 5.3, and 6.8 μM, respectively, increased ethanol production from 35.73 mM under standard metals concentration to 176.5, 187.8, 54.4, and 72.3 mM, respectively. Nickel was necessary for growth of C. ragsdalei. Growth rate (μ) of C. ragsdalei improved from 0.34 to 0.49 (day−1), and carbon monoxide dehydrogenase (CODH) and hydrogenase (H2ase)-specific activities improved from 38.45 and 0.35 to 48.5 and 1.66 U/mg protein, respectively, at optimum concentration of Ni2+. At optimum concentrations of WO4 and SeO4 , formate dehydrogenase (FDH) activity improved from 32.3 to 42.6 and 45.4 U/mg protein, respectively. Ethanol production and the activity of FDH reduced from 35 mM and 32.3 U/mg protein to 1.14 mM and 8.79 U/mg protein, respectively, upon elimination of WO4 from the medium. Although increased concentration of Zn2+ enhanced growth and ethanol production, the activities of CODH, FDH, H2ase and alcohol dehydrogenase (ADH) were not affected by varying the Zn2+ concentration. Omitting Fe2+ from the medium decreased ethanol production from 35.7 to 6.30 mM and decreased activities of CODH, FDH, H2ase and ADH from 38.5, 32.3, 0.35, and 0.68 U/mg protein to 9.07, 7.01, 0.10, and 0.24 U/mg protein, respectively. Ethanol production improved from 35 to 54 mM when Cu2+ was removed from the medium. The optimization of trace metals concentration in the fermentation medium improved enzyme activities (CODH, FDH, and H2ase), growth and ethanol production by C. ragsdalei.
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