Effect of trace metals on ethanol production from synthesis gas by the ethanologenic acetogen, Clostridium ragsdalei

The effect of trace metal ions (Co(2+), Cu(2+), Fe(2+), Mn(2+), Mo(6+), Ni(2+), Zn(2+), SeO(4) (-) and WO(4) (-)) on growth and ethanol production by an ethanologenic acetogen, Clostridium ragsdalei was investigated in CO:CO(2)-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 Ni(2+), Zn(2+), SeO(4) (-) and WO(4) (-) from 0.84, 6.96, 1.06, and 0.68 mu M in the standard trace metals solution to 8.4, 34.8, 5.3, and 6.8 mu M, 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 (mu) of C. ragsdalei improved from 0.34 to 0.49 (day(-1)), and carbon monoxide dehydrogenase (CODH) and hydrogenase (H(2)ase)-specific activities improved from 38.45 and 0.35 to 48.5 and 1.66 U/mg protein, respectively, at optimum concentration of Ni(2+). At optimum concentrations of WO(4) (-) and SeO(4) (-), 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 WO(4) (-) from the medium. Although increased concentration of Zn(2+) enhanced growth and ethanol production, the activities of CODH, FDH, H(2)ase and alcohol dehydrogenase (ADH) were not affected by varying the Zn(2+) concentration. Omitting Fe(2+) from the medium decreased ethanol production from 35.7 to 6.30 mM and decreased activities of CODH, FDH, H(2)ase 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 Cu(2+) was removed from the medium. The optimization of trace metals concentration in the fermentation medium improved enzyme activities (CODH, FDH, and H(2)ase), growth and ethanol production by C. ragsdalei.