利用纤维床反应器固定化发酵生产丙酸

构建了一种纤维床反应器(FBB), 并将其应用于丙酸的生产。将棉纤维绕成桶状, 固定于反应器中, 即可用于丙酸固定化发酵。以40 g/L的葡萄糖为碳源, 与游离细胞相比, 利用FBB生产丙酸, 丙酸产量由14.58 g/L提高至20.41 g/L, 发酵时间由120 h缩短至60 h。研究了不同糖浓度条件下FBB生产丙酸情况, 并将补料策略应用于丙酸发酵中。结果表明: 补料发酵能够有效改善Propionibacterium freudenreichii CCTCC M207015在高糖条件下丙酸对葡萄糖转化率较低、副产物较多的问题。经补料发酵280 h, 丙酸产量达45.91 g/L, 丙酸质量约占有机酸总质量比例为72.31%。     

Evaluation of antimicrobial activity of certain Chinese plants used in folkloric medicine

Six selected plants, belonging to 3 families from Nanjing of China, were extracted with the solvent 95% (v/v) ethanol to yield 11 extracts. The extracts were evaluated for their effects on the growth of eight clinical bacteria, two fungi and one yeast using a modified agar diffusion method. The results showed that the majority of the extracts investigated showed greater activities against the Gram-positive bacteria than against the Gram-negative bacteria, the fungi and the yeast. The strongest antimicrobial activity was exhibited by the stem extracts of Mahonia fortunei against multiresistant Staphylococcus aureus strains, followed by the stem extracts of Mahonia bealei, while Bacillus thuringiensis was the most sensitive to all extracts.     

Las-like quorum-sensing system negatively regulates both pyoluteorin and phenazine-1-carboxylic acid production in Pseudomonas sp. M18

A las-like quorum-sensing system in Pseudomonas sp. M18 was identified, which consisted of lasI and lasR genes encoding LuxI-LuxR type regulator. Several functions of the las system from strain M18 were investigated in this study. The chromosomal inactivation of either lasI or lasR by recombination increased the production of both pyoluteorin (Plt) and phenazine-1-carboxylic acid (PCA) by 4－5 fold and 2－3 fold over that of the wild type strain of M18, respectively. Production of both antibiotics was restored to wild-type levels after in trans complementation with the wild-type lasI or lasR gene. Ex-pression of the translational fusions pltA׳-׳lacZ and phzA׳-׳lacZ further confirmed the negative effect of lasI or lasR on both biosynthetic operons, and it was also demonstrated that the las system was related to the ability of swarming motility and the inhibition of cell growth.     

Involvement of insulin in early development of mouse one-cell stage embryos

Recent studies have suggested that growth factors and hormones play important roles in cell prolif-eration and differentiation during early embryonic development. In the present study, we examined the expression and localization of insulin in the mouse oocytes and one-cell stage embryos by quantitative ELISA, RT-PCR, Western blot and immunofluorescence. In the mouse oocytes and one-cell stage em-bryos, expression of insulin was uniformly distributed in the cytoplasm. We also examined the expres-sion, activity and localization of mTOR (mammalian target of rapamycin) and p70S6K. The expression of mTOR and p70S6K was not significantly different at the cell cycle of mouse one-cell stage embryos. mTOR and S6K were distributed evenly in the cytoplasm at G1, G2 and M phase phase, but at S phase, the distribution of mTOR and S6K was around the pronucleus. At different phases, the activity of mTOR fluctuated. We also used the PI3K specific inhibitor-Wortmannin to investigate the cleavage rate of eggs. The result showed that the rate obviously decreased. When the mTOR specific inhibitor Rapa-mycin was used, the first mitotic division of the mouse one-cell stage embryo was delayed. These re-sults suggested that insulin was expressed both in mouse oocytes and one-cell stage embryos, and may play functional roles in regulation of mouse early embryogenesis by activating the signal pathway of PI3K/PKB/mTOR/S6K.     

Cre reconstitution allows for DNA recombination selectively in dual-marker-expressing cells in transgenic mice

Cre/LoxP-based DNA recombination has been used to introduce desired DNA rearrangements in various organisms, having for example, greatly assisted genetic analyses in mice. For most applications, single gene promoters are used to drive Cre production for conditional gene activation/inactivation or lineage-tracing experiments. Such a manipulation introduces Cre in all cells in which the utilized promoter is active. To overcome the limited selectivity of single promoters for cell-type-specific recombination, we have explored the ‘dual promoter combinatorial control’ of Cre activity, so that Cre activity could be restricted to cells that express dual protein markers. We efficiently reconstituted Cre activity from two modified, inactive Cre fragments. Cre re-association was greatly enhanced by fusing the Cre fragments separately to peptides that can form a tight antiparallel leucine zipper. The co-expressed Cre fusion fragments showed substantial activity in cultured cells. As proof of principle of the utility of this technique in vivo for manipulating genes specifically in dual-marker-positive cells, we expressed each inactive Cre fragments in transgenic mice via individual promoters. Result showed the effective reconstitution of Cre activates LoxP recombination in the co-expressing cells.     

Hydrolase-catalyzed Michael addition of 1,3-dicarbonyl compounds to α,β-unsaturated compounds in organic solvent

A novel strategy to perform Michael additions between 1,3-dicarbonyl compounds and α,β-unsaturated compounds was developed by the catalysis of hydrolase. We found that 11 hydrolase could catalyze the enzymatic Michael addition reaction to form the carbon–carbon bond. In 2-methyl-2-butanol d-aminoacylase showed high Michael addition activity. The influence of substrate and Michael acceptor structure on Michael addition was evaluated systematically. Some control experiments demonstrated that the active site of d-aminoacylase was responsible for the enzymatic Michael addition reaction. This novel Michael addition activity of hydrolase is of practical significance in expanding the application of enzymes and in the evolution of new biocatalysts.     

Altered levels of histone deacetylase OsHDT1 affect differential gene expression patterns in hybrid rice

Hybrids between different inbred varieties display novel patterns of gene expression resulted from parental variation in allelic nucleotide sequences. To study the function of chromatin regulators in hybrid gene expression, the histone deacetylase gene OsHDT1 whose expression displayed a circadian rhythm was over-expressed or inactivated by RNAi in an elite rice parent. Increased OsHDT1 expression did not affect plant growth in the parent but led to early flowering in the hybrid. Nonadditive up-regulation of key flowering time genes was found to be related to flowering time of the hybrid. Over-expression of OsHDT1 repressed the nonadditive expression of the key flowering repressors in the hybrid (i.e. OsGI and Hd1) inducing early flowering. Analysis of histone acetylation suggested that OsHDT1 over-expression might promote deacetylation on OsGI and Hd1 chromatin during the peak expression phase. High throughput differential gene expression analysis revealed that altered OsHDT1 levels affected nonadditive expression of many genes in the hybrid. These data demonstrate that nonadditive gene expression was involved in flowering time control in the hybrid rice and that OsHDT1 level was important for nonadditive or differential expression of many genes including the flowering time genes, suggesting that OsHDT1 may be involved in epigenetic control of parental genome interaction for differential gene expression.