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Zi Jin,Shuli Liang,Xiuqin Zhang,Shuangyan Han,Changqiong Ren,Ying Lin,Suiping Zheng 한국생물공학회 2013 Biotechnology and Bioprocess Engineering Vol.18 No.2
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.
Shu Li,Liang Wang,Nan Wang,Wei Cong 한국생물공학회 2021 Biotechnology and Bioprocess Engineering Vol.26 No.4
A breeding approach combining genome shuffling with streptomycin resistance was developed in this research to improve the poly-γ-L-diaminobutanoic acid (γ-PAB) production in Bacillus pumilus LS-1. By this unique strategy, recombinants from the third round of genome shuffling could tolerate 18 μg/L of streptomycin and exhibited higher γ-PAB yield as 152.2 mg/L in shakeflask fermentation, 3-fold over the parent. In batch fermentation, B. pumilus GS3-9 could produce γ-PAB as high as 1284.7 mg/L in two days, 2.4-fold higher than the control, which was the highest productivity ever reported. In addition, the optimal pH in B. pumilus for γ-PAB synthesis was changed after atmospheric and room temperature plasma (ARTP) mutagenesis and protoplast fusion, because lower pH environment is favorable for accumulation of intracellular ATP. Some key enzymes in GS3-9 showed higher activities than those in parent, suggesting a greater flux to TCA circle and DAP pathway, which was a reason for enhanced γ-PAB production.