Due to its dense crystalline structure and extensive hydrogen bonding network, cellulose exhibits limited reactive accessibility and reactivity, which severely restricts the reaction efficiency, degree of substitution, and uniformity of cellulose modifications such as carboxymethylation. To overcome these limitations, this study developed a novel glycerol-based pretreatment strategy to disrupt the hydrogen bonding network of bacterial cellulose (BC), thereby improving its reactive accessibility. The results confirmed that glycerol pretreatment significantly enhanced the reactivity of BC. The reaction time for preparing carboxymethyl cellulose (CMC) from glycerol-pretreated powdered BC was reduced from 2 to 1 h, representing a 100% improvement in reaction efficiency. In addition, glycerol pretreatment facilitated the exposure of hydroxyl groups in BC, thereby increasing the degree of substitution of CMC from 0.297 to 0.433 and from 0.427 to a peak value of 0.626, an approximately 46% enhancement. In addition, the CMC films prepared from glycerol-pretreated BC exhibited significantly improved light transmittance, reaching over 95% in the wavelength range of 300-1000 nm. This study provides theoretical support and technical guidance for the efficient production of CMC, expands its application potential in high-end fields, and promotes the high-value utilization of cellulose resources.

该研究利用含有组成型启动子的质粒pET-20b载体,在大肠杆菌(Escherichia coli)BL21(DE3)中对3种D-阿洛酮糖3-差向异构酶进行异源表达,其后以D-果糖为底物进行静息细胞转化.结果表明,重组菌在摇床30℃、200 r/min转速下发酵48 h,能够利用D-果糖为底物生产D-阿洛酮糖,转化率分别达到27.56％、23.99％和25.98％.为降低D-果糖对D-阿洛酮糖纯化过程中的影响,在产糖的过程后偶联酿酒酵母(Saccharomycescerevisiae)好氧发酵过程,消耗掉混合糖液中的D-果糖,结果显示转化24 h后D-果糖去除率达到94.22％,该研究为下游D-阿洛酮糖的分离和纯化提供了新的思路.

2-癸烯酸是一种具有2位不饱和键的中链脂肪酸,是合成功能化合物10-羟基-2-癸烯酸的重要前体物质.本研究首先将硫脂酶基因YdiI和脂肪酸CoA脱氢酶基因FadA分别连接至具有pGAP启动子的pGAPZαA载体上,并电转化至毕赤酵母GS115感受态中,经过Zeocin抗性筛选及基因组PCR鉴定后,成功获得重组载体同源重组至毕赤酵母GS115基因组上的阳性重组子.采用气相色谱-质谱联用方法对发酵产物进行检测,结果发现培养12 h后发酵产物中有2-癸烯酸出现,在发酵24 h产量可达33.7 mg/L,这表明YdiI和FadA基因已成功转入毕赤酵母GS115中.本研究成功构建了能够合成2-癸烯酸的重组毕赤酵母GS115工程菌,为下一步利用毕赤酵母进一步合成10-羟基-2-癸烯酸打下基础.

Candida tropicalis can metabolize alkanes or fatty acids to produce long-chain dicarboxylic acids (DCAs). Fatty acid transporters located on the cell or peroxisome membrane may play an important role in this process. Using amino acid sequence homologous alignment, two putative proteins, CtFat1p and CtPxa1p, located on the cell and peroxisome membrane were found, respectively. Moreover, single- and double-knockout homologous recombination technology was used to study ctfat1p and ctpxa1p gene effects on DCA synthesis. In comparison to the wild-type strain, long-chain DCA yield decreased by 65.14%, 88.38% and 56.19% after single and double-copy knockout of ctfat1p genes and double-copy knockout of ctpxa1p genes, respectively, indicating that the knockout of ctfat1p and ctpxa1p genes had a significant effect on the conversion of oils and fats into long-chain DCAs by C. tropicalis. However, the yield of long-chain DCAs increased by 21.90% after single-knockout of the ctpxa1p gene, indicating that the single-knockout of the ctpxa1p gene may reduce fatty acid transport to peroxisome for further oxidation. Moreover, to improve the intracellular transport rate of fatty acids, ctfat1p copy number increased, increasing DCA yield by 30.10%. These results may provide useful information for enhancing the production of long-chain DCAs by C. tropicalis.

Corynebacterium glutamicum has a long and successful history in the biotechnological production of l-lysine. Besides the adjustment of metabolic pathways, intracellular and extracellular transport systems are critical for the cellular metabolism of l-lysine or its by-products. Here, three amino acid transmembrane transporters, namely, GluE, BrnE/BrnF, and LysP, which are widely present in C. glutamicum strains, were each investigated by gene knockout. In comparison with that in the wild-type strain, the yield of l-lysine increased by 9.0%, 12.3%, and 10.0% after the deletion of the gluE, brnE/brnF, and lysP genes, respectively, in C. glutamicum 23,604. Moreover, the amount of by-product amino acids decreased significantly when the gluE and brnE/brnF genes were deleted. It was also demonstrated that there was no effect on the growth of the strain when the gluE or lysP gene was deleted, whereas the biomass of C. glutamicum WL1702 (ΔbrnE/ΔbrnF) in the fermentation medium was significantly reduced in comparison with that of the wild type. These results also provide useful information for enhancing the production of l-lysine or other amino acids by C. glutamicum.