Abstract
Low aqueous solubility of the gases for autotrophic fermentations (e.g., hydrogen gas) results in low productivities in bioreactors. A frequently suggested approach to overcome mass transfer limitation is to increase the solubility of the limiting gas in the reaction medium by increasing the partial pressure in the gas phase. An increased inlet hydrogen partial pressure of up to 2.1 bar (total pressure of 3.5 bar) was applied for the autotrophic conversion of hydrogen and carbon dioxide with Acetobacterium woodii in a batch-operated stirred-tank bioreactor with continuous gas supply. Compared to the autotrophic batch process with an inlet hydrogen partial pressure of 0.4 bar (total pressure of 1.0 bar) the final acetate concentration after 3.1 days was reduced to 50 % (29.2 g L−1 compared to 59.3 g L−1), but the final formate concentration was increased by a factor of 18 (7.3 g L−1 compared to 0.4 g L−1). Applying recombinant A. woodii strains overexpressing either genes for enzymes in the methyl branch of the Wood–Ljungdahl pathway or the genes phosphotransacetylase and acetate kinase at an inlet hydrogen partial pressure of 1.4 bar reduced the final formate concentration by up to 40 % and increased the final dry cell mass and acetate concentrations compared to the wild type strain. Solely the overexpression of the two genes for ATP regeneration at the end of the Wood–Ljungdahl pathway resulted in an initial switch off of formate production at increased hydrogen partial pressure until the maximum of the hydrogen uptake rate was reached.
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Acknowledgments
The authors gratefully thank Prof. Peter Dürre (University of Ulm, Germany) for providing the strains used for this study. Furthermore, the support of Christina Kantzow by the TUM Graduate School is gratefully acknowledged.
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449_2016_1600_MOESM1_ESM.tif
S1: Overview of the Wood-Ljungdahl pathway including the representation of the engineered A. woodii strains. A. woodii pJIR750_THF overexpressing the genes for formyl-THF-synthetase, formyl-THF-cyclohydrolase, methylene-THF-dehydrogenase and methylene-THF-reductase is represented by red arrows and A. woodii pJIR750_pta-ack overexpressing the genes for the phosphotransacetylase and acetate kinase is represented by blue arrows
449_2016_1600_MOESM2_ESM.tif
S2: Reproduction of autotrophic batch fermentation processes with A. woodii wild type in a stirred-tank bioreactor (see Fig. 2). Concentrations of cell dry weight (a), acetate (b) and formate (c) as function of process time of two independently performed gas fermentations
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Kantzow, C., Weuster-Botz, D. Effects of hydrogen partial pressure on autotrophic growth and product formation of Acetobacterium woodii . Bioprocess Biosyst Eng 39, 1325–1330 (2016). https://doi.org/10.1007/s00449-016-1600-2
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DOI: https://doi.org/10.1007/s00449-016-1600-2