Immobilization of Acetobacter sp. CCTCC M209061 for efficient asymmetric reduction of ketones and biocatalyst recycling

Abstract

BackgroundThe bacterium Acetobacter sp. CCTCC M209061 is a promising whole-cell biocatalyst with exclusive anti-Prelog stereoselectivity for the reduction of prochiral ketones that can be used to make valuable chiral alcohols such as (R)-4-(trimethylsilyl)-3-butyn-2-ol. Although it has promising catalytic properties, its stability and reusability are relatively poor compared to other biocatalysts. Hence, we explored various materials for immobilizing the active cells, in order to improve the operational stability of biocatalyst.ResultsIt was found that Ca-alginate give the best immobilized biocatalyst, which was then coated with chitosan to further improve its mechanical strength and swelling-resistance properties. Conditions were optimized for formation of reusable immobilized beads which can be used for repeated batch asymmetric reduction of 4′-chloroacetophenone. The optimized immobilized biocatalyst was very promising, with a specific activity of 85% that of the free-cell biocatalyst (34.66 μmol/min/g dw of cells for immobilized catalyst vs 40.54 μmol/min/g for free cells in the asymmetric reduction of 4′-chloroacetophenone). The immobilized cells showed better thermal stability, pH stability, solvent tolerance and storability compared with free cells. After 25 cycles reaction, the immobilized beads still retained >50% catalytic activity, which was 3.5 times higher than degree of retention of activity by free cells reused in a similar way. The cells could be recultured in the beads to regain full activity and perform a further 25 cycles of the reduction reaction. The external mass transfer resistances were negligible as deduced from Damkohler modulus Da < <1, and internal mass transfer restriction affected the reduction action but was not the principal rate-controlling step according to effectiveness factors η < 1 and Thiele modulus 0.3<∅ <1.ConclusionsCa-alginate coated with chitosan is a highly effective material for immobilization of Acetobacter sp. CCTCC M209061 cells for repeated use in the asymmetric reduction of ketones. Only a small cost in terms of the slightly lower catalytic activity compared to free cells could give highly practicable immobilized biocatalyst.

Production of sorbitol by repeated batch fermentation using immobilized of Lactobacillus plantarum Strain (BAA-793) via Solid State Fermentation

“…Besides that, there were appearances of corrugation on the surface of the bead, as shown in Figure 2, which was similar to the previous observation of Chen et al (2012), which used scanning electron microscopy of Ca-alginate and alginate-chitosan beads containing Acetobacter cells (Chen et al, 2012).…”

Enzymatic synthesis of enantiopure alcohols: current state and perspectives

“…29 For instance, uoxetine, which is used for the treatment of depression among others mental disorders, and (R)-benzyl-4-hydroxyl-2-pentynoate, which is a potential therapeutic for Alzheimer's disease, are synthesized from the chiral intermediate secondary alcohol (R)-4-(trimethylsilyl)-3-butyn-2-ol, respectively. 30,31 (R)-2-Octanol was proven to be a precursor compound for the several optically active pharmaceuticals products. 32 Isoproterenol, is a pharmaceutical drug which treats bradycardia, and neobenodine, which has antihistaminic and anticholinergic action, and both are obtained from chiral secondary alcohols.…”

“…20 Secondary alcohols are the most frequently used molecules in lipase-catalysed kinetic resolutions not only because of their importance in organic synthesis but also because lipases usually show much higher enantioselectivity in resolutions towards secondary alcohols than in those towards primary or tertiary alcohols. 31 In enzymatic kinetic resolutions of secondary alcohols, the outcome is normally highly predictable, and it follows Kazlauskas' rule. 40 Usually, the (R)-alcohol is converted into (R)-acetate at a higher rate than its antipode with high ee, leaving the (S)-alcohol as an enantiomerically pure unreacted enantiomer.…”

Performance analysis of immobilized and co-immobilized enriched-mixed culture for hydrogen production

“…Alginates with concentration below 1.5% produced non spherical and very fragile beads [36][37], whereas 23% concentration of alginate produced spherical and strong beads [37]. A research by Kong et al [38] demonstrated that the alginate concentration above 4% caused a very viscous solution, so it was difficult to produce spherical beads.…”