Immobilized and Free Cells of Geotrichum candidum for Asymmetric Reduction of Ketones: Stability and Recyclability

Abstract

Marine-derived fungus Geotrichum candidum AS 2.361 was previously reported by our group as an active strain for the enantioselective reduction of ketones. Although some other Geotrichum strains were also found from the terrestrial sources, information on their stability and reusability is scarce. Herein, the stabilities—in terms of pH tolerance, thermostability, and storage stability, and reusability—of G. candidum AS 2.361 were described for the asymmetric reduction of a series of aromatic ketones. Two differently immobilized cells (agar immobilization and calcium alginate immobilization) as well as free cells were prepared. For three substrates (1-(3-bromophenyl) ethan-1-one (1b), 1-(2-chlorophenyl) ethan-1-one (1d), and acetophenone (1g)) immobilized cells on agar showed a great improvement in the bioreduction activities compared to the free cells, increasing yields up to 97% with ee values of 99%. Cells immobilized on agar/calcium alginate could maintain more than 90% of the original activities within the assayed pH ranges of 3.5–11, while free cells were highly sensitive to alkaline and acidic conditions. Concerning thermostability, immobilized cells on agar kept 99% of their original activities after incubation at 60 °C for 1 h, while almost no activity was detected for the free cells under the same condition. Immobilized cells were stable at 4 °C for 80 days without any activity loss, while free cells started to decrease the activity after storage at 4 °C for six days. The immobilized cells retained almost 99% activity after four reuse cycles, while free cells lost almost all the activities at on the third cycle.

Rapid Degradation of Hazardous Amides by Immobilized Engineered Pseudomonas putida KT2440 Based on a Novel Gene Expression Vector

“…Peaks of free P. putida KT2440 pLSJ15-amiA at 3306, 2928, 1655, and 1078 cm –1 (Figure A) corresponded to the stretching vibrations of O–H, C–H, CO, and C–O, respectively. − The peaks at 3427 cm –1 (O–H stretching vibration), 1631 cm –1 (−COO asymmetric stretching vibration), 1429 cm –1 (−COO symmetric stretching vibration), and 1028 cm –1 (C–O–C stretching vibration) were the characteristic peaks of native calcium alginate (Figure C) . Compared with the spectra of free P.…”

Marine-derived fungi as biocatalysts

“…That same year, Liu et al (2018b) studied immobilized and free cells of Geotrichum candidum for the asymmetric reduction of aromatic ketones. The marine fungus G. candidum was isolated from the Chinese cnidarian zoanthid, P. variabilis, collected from Zhuhai City.…”

Enhanced upgrading of corncob to furfuryl alcohol with a novel silica-supported SO42−-TiO2 chemocatalyst and immobilized whole-cell biocatalyst

“…33,34 Whole cells can be regarded as microreactors that contain enzymes and all the necessary cofactors. 35 The adoption of whole cells biocatalysis offers further advantages over the adoption of enzymatic biocatalysis. However, the free cells are easily inactivated in solution and have a short service life, which limits the subsequent product separation and purification.…”