Effects of hydrogen partial pressure on autotrophic growth and product formation of Acetobacterium woodii.

Low aqueous solubility of the gases for autotrophic fermentations (e.g., hydrogen gas) results in low productivities in bioreactors.

Continuous gas fermentation by Acetobacterium woodii in a submerged membrane reactor with full cell retention.

Acetogenic bacteria like Acetobacterium woodii represent an ancient group of anaerobic microorganisms which use hydrogen and carbon dioxide to produce acetate. Cell concentrations and space-time yields are usually low in gas fermentations. A standard stirred‑tank bioreactor with continuous gas supply was equipped with a customized submerged microfiltration unit.

Multi-enzymatic one-pot reduction of dehydrocholic acid to 12-keto-ursodeoxycholic acid with whole-cell biocatalysts.

Ursodeoxycholic acid (UDCA) is a bile acid of industrial interest as it is used as an agent for the treatment of primary sclerosing cholangitis and the medicamentous, non-surgical dissolution of gallstones. Currently, it is prepared industrially from cholic acid following a seven-step chemical procedure with an overall yield of <30%. In this study, we investigated the key enzymatic steps in the chemo-enzymatic preparation of UDCA-the two-step reduction of dehydrocholic acid (DHCA) to 12-keto-ursodeoxycholic acid using a mutant of 7β-hydroxysteroid dehydrogenase (7β-HSDH) from Collinsella aerofaciens and 3α-hydroxysteroid dehydrogenase (3α-HSDH) from Comamonas testosteroni.