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

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.

Commercial Biomass Syngas Fermentation

“…"C. ragsdalei" or strain "P11" was isolated from duck pond sediment by researchers from The University of Oklahoma and Oklahoma State University and is described in a patent [154]. "C. ragsdalei" has been explored for the production of ethanol from syngas [155][156][157], with growth temperatures of 32 °C-37 °C [157] and a batch fermentation reported ethanol concentration of 1.99 g L −1 [158]. In a 100 L stirred tank reactor (STR) an ethanol concentration of 25.26 g L −1 was achieved over a fermentation duration of 59 days [159].…”

Kinetic Models and Effects of Mn(II) Ion on Ethanol Production from Cornstalks

“…However, the addition of Mn 2+ has no significant effect on sugar yield, and the saccharification yields for the samples with Mn 2+ are the same or similar to those of the saccharification samples without added metal ions (Ramachandran et al 2015). Ethanol production does not change considerably at higher concentrations of Mn 2+ (Saxena and Tanner 2011). However, trace manganese enhances butyric acid production (Liu et al 2015).…”

“…Mn 2+ is an essential trace element for microbial growth that improves the activity of cellulase and yeast (Saxena and Tanner 2011;Lakkana et al 2012). The increase in activity and cellulose content is favorable for fermentation (Li et al 2013;Deesuth et al 2015).…”

“…However, trace manganese enhances butyric acid production (Liu et al 2015). Moreover, supplementation with Mn 2+ and nitrogen coupled with a small amount of aeration improves ethanol production efficiency (Saxena and Tanner 2011;Deesuth et al 2015). However, high concentration of Mn 2+ may be toxic because it affects the permeability of membranes, causing a decrease in both yeast growth and fermentation activity (Stehlik-Tomas et al 2004).…”

A review of conversion processes for bioethanol production with a focus on syngas fermentation

“…Studies with C. ljungdahlii showed that reducing or completely removing YE from fermentation medium increased ethanol concentration from 1 g/L to 48 g/L (Phillips et al, 1993;Vega et al, 1989). The increase in the concentrations of Ni 2+ , Zn 2+ , SeO4 -and WO4 -from 0.84 µM, 6.96 µM, 1.06 µM and 0.68 µM to 8.4 µM, 34.8 µM, 5.3 µM and 6.8 µM, respectively, improved ethanol production by C. ragsdalei by fourfold (Saxena and Tanner, 2011).…”