Earlier studies on fructose laurate ester products have shown that recombinant Pichia pastoris displaying Candida antarctica lipase B (CALB) on the cell surface acts as an efficient whole-cell biocatalyst for sugar ester production from fructose and lauric acid in an organic solvent. The effects of various reaction factors, including solvent composition, substrate molar ratio, enzyme dose, temperature and water activity, on esterification catalyzed by the CALB-displaying P. pastoris whole-cell biocatalyst were examined in the present study. Under the preferred reaction conditions, specifically, 5 mL organic solvent mixture of 2-methyl-2-butanol/DMSO (20% v/v), 2 mmol fructose with a lauric acid to fructose molar ratio of 2:1, 0.3 g whole-cell biocatalyst (1,264 U/g dry cell) with an initial water activity of 0.11, 1.2 g 4Å molecular sieve, reaction temperature of 55oC and 200 rpm stirring speed, the fructose mono laurate ester yield was 78% (w/w). The CALBdisplaying P. pastoris whole-cell biocatalyst exhibited good operational stability, with an evident increase, rather than decrease, in relative activity after the continuous recover and reuse cycle. The relative activity of the biocatalyst remained 50% higher than that of the first batch, even following reuse for 15 batches. Our results collectively indicate that the CALB-displaying P. pastoris whole-cell biocatalyst may be potentially utilized in lieu of free or immobilized enzyme to effectively produce non-ionic surfactants such as fatty acid sugar esters, offering the significant advantages of cost-effectiveness, good operational stability and mild reaction conditions.
Dirigent (DIR) and DIR-like family genes were involved in lignification or in the response to pathogen infection and abiotic stress in plants. Little is known to us about how rice DIR genes respond to adverse conditions. In this study, we reported genome-wide analysis of 49 DIR or DIR-likes genes in rice. The 49 OsDIRs or OsDIR-likes were tandem arranged into ten clusters. The phylogenetic analysis indicated that the 49 rice DIR and DIR-like genes cluster into five distinct subfamilies, DIR-a and four DIR-like subfamilies (DIR-b/d, and DIR-g, DIR-c, DIR-e). Meta-analysis of microarray gene expression datas indicated that all the OsDIRs or OsDIR-likes were expressed almost at the same level but with different patterns: most OsDIRs or OsDIR-likes were expressed exclusively in stigma and ovary and were induced by IAA and BAP; several genes were induced by trans-zeatin (tZ) and DMSO; 23 OsDIRs or OsDIR-likes were responded to abiotic stress. Our analysis also showed that most of these genes could respond to abiotic stresses, which contained cis-regulatory elements. The present study will provide a useful reference for further functional analysis of the DIR genes in rice. 相似文献