木质纤维素水解抑制物耐受基因筛选和鉴定

以竹屑、秸秆等为代表的木质纤维素原料用于生产燃料乙醇近年来备受关注,但是在水解过程中会产生大量的毒性物质会抑制酿酒酵母的乙醇发酵。为了不增加生产成本,提高毒性抑制物在应激条件下的发酵效率,筛选酿酒酵母中对这些抑制物广谱耐受基因至关重要。通过全基因组敲除文库扫描、生物信息学分析和基因回补验证,筛选出了酿酒酵母中对代表性抑制物糠醛、苯酚、乙酸以及三者混合抑制剂耐受的共有基因,分别是ASC1、ISC1、DRS2、RIC1、RPE1、YPT6、SEC66和ERG2;根据基因功能分析,明确了转录调控、信号转导、氧化应激耐受、麦角甾醇生物合成、自噬和内吞作用等蛋白与木质纤维素水解液复合抑制剂耐受相关。研究结果对燃料乙醇发酵的工程菌株改造具有重要借鉴意义。

微生物基因组精简优化的研究进展

微生物基因组精简优化是构建合成生物学底盘细胞的重要策略。文中从基因组精简的整体设计出发,归纳了微生物的必需基因及其确定方法,重点介绍了各种微生物基因组精简策略,分析了多种基因组精简菌株的特点,充分展示了基因组精简优化在构建合成生物学底盘细胞中的重要作用。

大肠杆菌最小基因组分析和删减进展

大肠杆菌是基础研究最透彻、应用广泛的微生物,构建含减小甚至是最小基因组的大肠杆菌将为合成生物学的研究和应用提供理想的底盘生物。介绍了大肠杆菌最小基因组的生长与繁殖必需基因的生物信息学分析和实验鉴定,基因组敲除技术,以及删减基因组的大肠杆菌菌株的构建和应用等方面的研究进展。

Engineering of Corynebacterium glutamicum to Enhance L-ornithine Production by Gene Knockout and Comparative Proteomic Analysis

Engineered Corynebacterium glutamicum was constructed for L-ornithine production by disrupting genes of argF and proB to prevent the flux away from L-ornithine.Effect of the inactivation of 2-oxoglutarate de-hydrogenase complex(ODHC) on L-ornithine production was also investigated.It was found that the inactivation of ODHC by knockout of the kgd gene enhanced L-ornithine production.The engineered C.glutamicum ATCC13032(ΔargFΔproBΔkgd) produced L-ornithine up to 4.78 g·L-1 from 0.24 g·L-1 of the wild-type strain.In order to understand the mechanism of L-ornithine production in C.glutamicum ATCC13032(ΔargFΔproBΔkgd) and find out new strategies for further enhancing L-ornithine production,the comparative proteome between the wild-type and the engineered strain was analyzed.L-Ornithine overproduction in the engineered strain was related to the up-regulation of the expression levels of enzymes involved in L-ornithine biosynthesis pathway and down-regulation of the expression levels of proteins involved in pentose phosphate pathway.The overexpression of genes in the upstream pathway of glutamate to increase the availability of endogenous glutamate may further in-crease ornithine production in the engineered C.glutamicum and the ornithine synthesis enzymes(ArgCJBD) may not be the limiting enzymes in the engineered C.glutamicum.

Epigenetic Repression of SATB1 by Polycomb Group Protein EZH2 in Epithelial Cells

Objective To study the regulatory mechanism of SATB1 repression in cells other than T cells or erythroid cells, which have high expression level of SATB1. Methods HeLa epithelial cells were treated with either histone deacetylase inhibitor (HDACi) trichostatin A (TSA) or DNA methylation inhibitor 5-Aza-C before detecting SATB1 expression. Luciferase reporter system was applied to measure effects of EZH2 on SATB1 promoter activity. Over-expression or knockdown of EZH2 and subsequent quantitative reverse transcription-polymerase chain reaction were performed to determine the effect of this Polycomb group protein on SATB1 transcription. Chromatin immunoprecipitation (ChIP) assay was applied to measure enrichment of EZH2 and trimethylated H3K27 (H3K27me3) at SATB1 promoter in HeLa cells. K562 cells and Jurkat cells, both having high-level expression of SATB1, were used in the ChIP experiment as controls. Results Both TSA and 5-Aza-C increased SATB1 expression in HeLa cells. Over-expression of EZH2 reduced promoter activity as well as the mRNA level of SATB1, while knockdown of EZH2 apparently enhanced SATB1 expression in HeLa cells but not in K562 cells and Jurkat cells. ChIP assay results suggested that epigenetic silencing of SATB1 by EZH2 in HeLa cells was mediated by trimethylation modification of H3K27. In contrast, enrichment of EZH2 and H3K27me3 was not detected within proximal promoter region of SATB1 in either K562 or Jurkat cells. Conclusion SATB1 is a bona fide EZH2 target gene in HeLa cells and the repression of SATB1 by EZH2 may be mediated by trimethylation modification on H3K27.

Impact of asialoglycoprotein receptor deficiency on the development of liver injury

The asialoglycoprotein （ASGP） receptor is a wellcharacterized hepatic receptor that is recycled via the common cellular process of receptor-mediated endocytosis （RME）. The RME process plays an integral part in the proper trafficking and routing of receptors and ligands in the healthy cell. Thus, the missorting or altered transport of proteins during RME is thought to play a role in several diseases associated with hepatocyte and liver dysfunction. Previously, we examined in detail alterations that occur in hepatocellular RME and associated receptor functions as a result of one particular liver injury, alcoholic liver disease （ALD）. The studies revealed profound ethanol- mediated impairments to the ASGP receptor and the RME process, indicating the importance of this receptor and the maintenance of proper endocytic events in normal tissue. To further clarify these observations, studies were performed utilizing knockout mice （lacking a functional ASGP receptor） to which were administered several liver toxicants. In addition to alcohol, we examined the effects following administration of anti- Fas （CD95） antibody, carbon tetrachloride （CCh） and lipopolysaccharide （LPS）/galactosamine. The results of these studies demonstrated that the knockout mice sustained enhanced liver injury in response to all of the treatments, as shown by increased indices of liver damage, such as enhancement of serum enzyme levels, histopathological scores, as well as hepatocellular death. Overall, the work completed to date suggests a possible link between hepatic receptors and liver injury. In particular, adequate function and content of the ASGP receptor may provide protection against various toxinmediated liver diseases.

Deletions are easy detectable in cochlear mitochondrial DNA of Cu/Zn superoxide dismutase gene knockout mice

Abstract Objectives To investigate the tissue specificity of reactive oxygen species (ROS) damage to mitochondrial DNA (mtDNA) and to determine whether cochlear mtDNA is a sensitive target for ROS damage. Methods 10 Cu/ZnSOD gene (Cu/Zn superoxide dismutase gene, Sod1) knockout mice and 16 wild-type mice were analyzed by nested polymerase chain reaction (PCR).Results Three deletions were detected in various tissues of Sod1 knockout mice. MtDNA3867bp and mtDNA3726bp deletions were the most visible, and mtDNA4236bp deletion was barely detected in these tissues. There were obvious differences in the ratio of deleted mtDNA/total mtDNA in different tissue. Deleted mtDNA was most abundant in the liver and kidney and less in cochlea, heart and brain. The lowest was in spleen and skin. The ratio in various tissues was 3-20 times in Sod1 knockout mice over wild-type mice. In cochlea, the ratio was about 15. Conclusions Without the protection of Sod1, ROS can lead to mtDNA deletions in various tissues with significant tissue specificity. Cochlear mtDNA is a sensitive target for ROS damage.