Selective Reduction Of 5-hydroxymethylfurfural By Meyerozyma Guilliermondii SC1103 Cells

5-Hydroxymethylfufural(HMF)is a useful bio-based platform chemical,which could be prepared via carbohydrate dehydration.There are a furan ring,formyl and hydroxymethyl groups in HMF,which could be transformed into a series of valuable intermediates by chemical modifications.2,5-Bis(hydroxymethyl)-furan(BHMF)that is the hydrogenation product of the formly group in HMF is a versatile building block for the synthesis of bio-based polymers,drugs,macrocyclic polyether compounds,and crown ethers.Presently,BHMF is still mainly synthesized by chemical methods,which were generally associated with serious environmental pollution,low selectivity and harsh conditions.Compared to chemical approaches,biocatalysis has attracted increasing interest in organic transformations because of many advantages such as being environmentally-friendly,high selectivity and mild reaction conditions.Using of whole cells as biocatalysts for the redox reactions not only makes enzymes encapsulated in cell membrane keep their catalytic activities,but also facilitates in situ regeneration of cofactors.Therefore,whole cells appreared to be superior to isolated enzymes for selectivie reduction of HMF to BHMF.However,to date,there are limited reports on biocatalytic reduction of HMF in the literature.A new highly HMF-tolerant yeast strain Meyerozyma guilliermondii SC1103 was isolated from the soil around the factory.Subsequently,the catalytic performance of the yeast cells and the effects of key factors on whole-cell biocatalytic synthesis of BHMF from HMF were investigated.An efficient and selective biocatalytic approach toward BHMF was established.Finally,porous metal-organic frameworks(MOFs)were evaluated as potential materials for immobilizing M.guilliermondill SC1103 cells,and the catalytic activities and the stability of the cells were compared before and after nanoencapsulation in MOFs.The results showed that the cosubstrate exhibited a significant effect on the catalytic activity,selectivity and substrate tolerance of the microbial cells,but the nitrogen source and the mineral salts exerted no significant effect.In addition,M.guilliermondii SC1103 cells showed good catalytic activity under pH 4.0-10.0.The yeast was highly tolerant to both HMF(up to 110 mM)and BHMF(up to 200 mM).Moreover,100 mM HMF was selectively reduced to BHMF within 12 h by the yeast cells under optimal conditions with the yield of 86% and the selectivity of > 99%.And even,the production of 191 mM of BHMF was realized within 24.5 h by using a fed-batch strategy,with a productivity of approximately 24 g/L d.Additionally,this new biocatalytic approach was also applied for the reduction of furfural and 5-methylfurfural,affording the corresponding furfuryl alcohols with the yields of 83 and 89%,and the selectivities of 96% and >99%,respectively.MOFs(e.g.,ZIF-8)could assemble quikly on the surface of the yeast cells,resulting in nanoencapsulation of the cells.And the encapsulation percentage of ZIF-8 on the cell surface approaches to 99%.It was found that the catalytic activity of the cells encapsulated in ZIF-8 was much higher than that of those encapsulated in calcium alginate,which may be attributed to the thin nanoshell of the former,thus significantly reducing mass transfer limitation.ZIF-8-coated cells exhibited high resistance against lyticase as well as storage stability.After storage for 28 days,the immobilized cells kept the residual activity of 61%,and the cell viability was up to 93%.The storage stability of the immobilized cells was comparable to that of free cells,demonstrating the high biocompatibility of ZIF-8.In addition,the immobilized cells displayed goodoperational stability,the relative yield of BHMF was up to 98% when they were reused for 5 runs in the reduction of HMF.Unfortunately,no significant improvements in the thermostability of the cells and their tolerance to HMF and organic solvents were observed after nanoencapsulation.In addition,MOF(Fe-BTC)also could quickly encapsulate cells,and Fe-BTC-coated cells had a good catalytic activity.The catalytic performances of whole cells have been uncovered in selective reduction of HMF in this work,which enrich the theortical foundation for biocatalytic valorization of bio-based chemicals.In addition,a new approach for immobilizing cells with MOF has been established,which may open up new opportunities for biocatalysis and engineering cell surfaces,due to the structural and chemical diversity of MOFs.