Dyadic (Netherlands)

Carbon dioxide utilization is a key strategy for sustainable chemical production and climate change mitigation. Microbial electrosynthesis (MES) offers a promising approach to convert CO₂ into organic acids and multi‑carbon compounds, but its industrial application requires improved product recovery methods. In this study, we developed an integrated MES-sorption-distillation system for the recovery of pure hexanoic acid. Adsorption experiments identified conditions for C6-selective capture from C2–C6 carboxylate mixtures typically produced from MES. Subsequent desorption using CO₂ expanded methanol enriched hexanoic acid concentration by 13-fold compared to the aqueous feed, achieving 67 % recovery in a single pass, but 100 % overall, since recirculation of unrecovered carboxylates back to the MES reactor is proposed. This recirculation will enhance chain elongation, eliminate loss of unrecovered carboxylates, and reduce the need for external pH control during MES. Distillation of the desorbed mixture led to streams of pure products and reusable solvent, without losses. Notably, 87 % of the total energy demand for product formation is attributed to the MES stage, where electrical energy is directly supplied as electrons to drive microbial production. Thus, MES with the proposed recovery method enables pure hexanoic acid production with minimal losses of materials or energy and potentially allows the system to operate in a carbon-negative manner. • An integrated MES–adsorption–desorption–distillation process was developed for C6 acid recovery. • CO₂-expanded methanol enabled >13-fold enrichment and >99 % recovery of hexanoic acid. • Heat-integrated distillation achieved >99.9 % product purity with 65 % lower energy consumption. • All waste streams were internally recycled; green electricity enables carbon-negative operation. • The system was experimentally validated and designed to be scalable for practical implementation.

Genes of β-mannosidase 97 kDa, GH family 2 (bMann9), β-mannanase 48 kDa, GH family 5 (bMan2), and α-galactosidase 60 kDa, GH family 27 (aGal1) encoding galactomannan-degrading glycoside hydrolases of Myceliophthora thermophila C1 were successfully cloned, and the recombinant enzymes were purified to homogeneity and characterized. bMann9 displays only exo-mannosidase activity, the K(m) and k(cat) values are 0.4 mM and 15 sec(-1) for p-nitrophenyl-β-D-mannopyranoside, and the optimal pH and temperature are 5.3 and 40°C, respectively. bMann2 is active towards galactomannans (GM) of various structures. The K(m) and k(cat) values are 1.3 mg/ml and 67 sec(-1) for GM carob, and the optimal pH and temperature are 5.2 and 69°C, respectively. aGal1 is active towards p-nitrophenyl-α-D-galactopyranoside (PNPG) as well as GM of various structures. The K(m) and k(cat) values are 0.08 mM and 35 sec(-1) for PNPG, and the optimal pH and temperature are 5.0 and 60°C, respectively.

Modification of Xanthophyllomyces dendrorhous toward a higher carotenoid synthesis will make the exploitation of X. dendrorhous as a natural source for astaxanthin more competitive. By recombinant DNA technology, the X. dendrorhous isopentenyl-pyrophosphate isomerase-encoding gene (idi) was inserted in a X. dendrorhous expression cassette that directs expression by the endogenous glyceraldehyde-3-phosphate dehydrogenase gene expression signals. X. dendrorhous transformation vector pPR2TN was used to deliver this expression cassette, by means of electroporation, into the ribosomal DNA of X. dendrorhous strain CBS 6938, which was confirmed by Southern analysis. High-performance liquid chromatography analysis of the carotenoids produced by idi-overexpressing transformant strains indicated a lower overall carotenoid formation when compared to the control strain. This finding is in contrast to that observed in bacterial systems, where enhanced expression of the idi gene increases the carotenoid content.