Host cell RecA activates a mobile element-encoded mutagenic DNA polymerase

Homologs of the mutagenic Escherichia coli DNA polymerase V (pol V) are encoded by numerous pathogens and mobile elements. We have used Rum pol (RumA′₂B), from the integrative conjugative element (ICE), R391, as a model mobile element-encoded polymerase (MEPol). The highly mutagenic Rum pol is transferred horizontally into a variety of recipient cells, including many pathogens. Moving between species, it is unclear if Rum pol can function on its own or requires activation by host factors. Here, we show that Rum pol biochemical activity requires the formation of a physical mutasomal complex, Rum Mut, containing RumA′₂B-RecA-ATP, with RecA being donated by each recipient bacteria. For R391, Rum Mut specific activities in vitro and mutagenesis rates in vivo depend on the phylogenetic distance of host-cell RecA from E. coli RecA. Rum pol is a highly conserved and effective mobile catalyst of rapid evolution, with the potential to generate a broad mutational landscape that could serve to ensure bacterial adaptation in antibiotic-rich environments leading to the establishment of antibiotic resistance.     

LGR5 regulates osteogenic differentiation of human thoracic ligamentum flavum cells by Wnt signalling pathway

Thoracic ossification of the ligamentum flavum (TOLF) is ectopic ossification of the spinal ligaments. Histologically, the development of TOLF can be described as the process of endochondral ossification. However, the underlying aetiology has not been completely clarified. In this investigation, the gene expression profile associated with leucine‐rich repeat‐containing G‐protein‐coupled receptors (LGR) and Wnt signalling pathway in the thoracic ligamentum flavum cells (TLFCs) of different ossification stages was analysed via RNA sequencing. We further confirmed the significant differences in the related gene expression profile by Gene Ontology (GO) enrichment analysis. LGR5 was first identified in primary human TLFCs during osteogenic differentiation. To evaluate the effect of LGR5 on osteogenic differentiation, LGR5 has been knocked down and overexpressed in human TLFCs. We observed that the knockdown of LGR5 inhibited the activity of Wnt signalling and attenuated the potential osteogenic differentiation of TLFCs, while overexpression of LGR5 activated the Wnt signalling pathway and increased osteogenic differentiation. Our results provide important evidence for the potent positive mediatory effects of LGR5 on osteogenesis by enhancing the Wnt signalling pathway in TOLF.     

A new bacteria-free strategy induced by MaGal2 facilitates pinewood nematode escape immune response from its vector beetle

Symbiotic microbes play a crucial role in regulating parasite–host interactions; however, the role of bacterial associates in parasite–host interactions requires elucidation. In this study, we showed that, instead of introducing numerous symbiotic bacteria, dispersal of 4th-stage juvenile (J_IV) pinewood nematodes (PWNs), Bursaphelenchus xylophilus, only introduced few bacteria to its vector beetle, Monochamus alternatus (Ma). J_IV showed weak binding ability to five dominant bacteria species isolated from the beetles’ pupal chamber. This was especially the case for binding to the opportunistic pathogenic species Serratia marcescens; the nematodes’ bacteria binding ability at this critical stage when it infiltrates Ma for dispersal was much weaker compared with Caenorhabditis elegans, Diplogasteroides asiaticus, and propagative-stage PWN. The associated bacterium S. marcescens, which was isolated from the beetles’ pupal chambers, was unfavorable to Ma, because it caused a higher mortality rate upon injection into tracheae. In addition, S. marcescens in the tracheae caused more immune effector disorders compared with PWN alone. Ma_Galectin2 (MaGal2), a pattern-recognition receptor, was up-regulated following PWN loading. Recombinant MaGal2 protein formed aggregates with five dominant associated bacteria in vitro. Moreover, MaGal2 knockdown beetles had up-regulated prophenoloxidase gene expression, increased phenoloxidase activity, and decreased PWN loading. Our study revealed a previously unknown strategy for immune evasion of this plant pathogen inside its vector, and provides novel insights into the role of bacteria in parasite–host interactions.     

不同植物生长调节剂对中华猕猴桃扦插生根的影响

以中华猕猴桃"桂海4号"为试材,采用500mg·L-1、1000mg·L-1、1500mg·L-1三种不同浓度的吲哚丁酸、萘乙酸、和ABT生根粉处理插条,进行了猕猴桃扦插试验。结果表明:吲哚丁酸1500mg·L-1的扦插生根率极显著高于萘乙酸和ABT生根粉的各个处理,显著高于吲哚丁酸1000mg·L-1;吲哚丁酸对根数和根长的促进作用优于萘乙酸和ABT生根粉,ABT生根粉对于根粗的促进作用却较其它两者强;主成分分析结果表明,吲哚丁酸1500mg·L-1处理的插条生长情况最好。     

四合木种群的生态适应性

通过四合木异地播种生长量比较、以及四合木对土壤的适应性和对水热综合因子的适应性分析,得到如下结果：（1）四合木生长量高低的顺序为乌海区的东胜土（12．12g）〉乌海区的乌海土（10．62g）〉东胜区的乌海土（3．10g）〉东胜区的东胜土（2．59g）。同一地区不同土壤间四合木生长量之间没有差异（P≥0．05）,不同地区相同土壤间的生长量之间却有十分显著的差异,说明了土壤条件对四合木的生存影响是次要的,气候条件是保证四合木生存的最重要的条件。（2）四合木分布区与异地保护区之间9种土壤微量元素具有差异,但由于四合木植株中的微量元素含量均高于土壤中的有效量,说明四合木对微量元素具有富集作用,土壤微量元素含量不是四合木成活与生长的限制因子。（3）四合木分布区与异地保护区之间各月平均温度差异显著;全年气温日较差以及温暖指数、寒冷指数、湿润指数和水热综合因子指数差异显著;生长季地表地温昼夜温差具有特殊性,这可能是异地保护不易成功的限制因子之一。     

强化产电微生物与电极间电子传递速率的研究进展

产电微生物是微生物燃料电池、电解池和电合成等微生物电化学技术(Microbial electrochemical technologies,METs)的研究基础.产电微生物与电极界面间的胞外电子传递(Extracellular electron transfer,EET)效率低以及生物被膜形成能力弱限制了METs在有机...     

培养和非培养法分析冷藏鸡肉胴体中的细菌多样性

运用纯培养和非培养法对冷藏鸡肉胴体上细菌多样性进行了对比研究。采用培养法从鸡肉胴体中初步分离到45株细菌菌株,16S rDNA-ARDRA分析得到9株代表性细菌,其16S rDNA序列系统发育分析表明,这些菌株隶属于Bacillus sp.、Shigella sp.、Pseudomonas sp.、Citrobacter sp.、Klebsiella sp.和Escherichia sp.6个属。16S rDNA-ARDRA联合PAGE和16S rDNA全序列分析的非培养法结果表明,冷藏鸡肉中细菌主要属于Acinetobacter sp.、Bacillus sp.、Acidovorax sp.、Brochothrix thermosphacta、Lactococcus garvieae和Leuconostoc lactis等16个属。非培养法揭示的细菌多样性比培养法丰富,但二者结合使用能让肉品中微生物多样性得到更全面的展示。     

mTORC1-independent translation control in mammalian cells by methionine adenosyltransferase 2A and S-adenosylmethionine

Methionine adenosyltransferase (MAT) catalyzes the synthesis of S-adenosylmethionine (SAM). As the sole methyl-donor for methylation of DNA, RNA, and proteins, SAM levels affect gene expression by changing methylation patterns. Expression of MAT2A, the catalytic subunit of isozyme MAT2, is positively correlated with proliferation of cancer cells; however, how MAT2A promotes cell proliferation is largely unknown. Given that the protein synthesis is induced in proliferating cells and that RNA and protein components of translation machinery are methylated, we tested here whether MAT2 and SAM are coupled with protein synthesis. By measuring ongoing protein translation via puromycin labeling, we revealed that MAT2A depletion or chemical inhibition reduced protein synthesis in HeLa and Hepa1 cells. Furthermore, overexpression of MAT2A enhanced protein synthesis, indicating that SAM is limiting under normal culture conditions. In addition, MAT2 inhibition did not accompany reduction in mechanistic target of rapamycin complex 1 activity but nevertheless reduced polysome formation. Polysome-bound RNA sequencing revealed that MAT2 inhibition decreased translation efficiency of some fraction of mRNAs. MAT2A was also found to interact with the proteins involved in rRNA processing and ribosome biogenesis; depletion or inhibition of MAT2 reduced 18S rRNA processing. Finally, quantitative mass spectrometry revealed that some translation factors were dynamically methylated in response to the activity of MAT2A. These observations suggest that cells possess an mTOR-independent regulatory mechanism that tunes translation in response to the levels of SAM. Such a system may acclimate cells for survival when SAM synthesis is reduced, whereas it may support proliferation when SAM is sufficient.     

草原沙漠化过程中植物的耐胁迫类型研究

以内蒙古锡林郭勒盟多伦县草原沙漠化过程中不同梯度共有种群为研究对象 ,探讨植物的受损机理 ,综合 2 0 0 1～ 2 0 0 3年的研究结果表明 :随着沙漠化的进展 ,共有种群的 1叶片含水量及叶绿素 a、b和总叶绿素含量均呈降低趋势。叶片含水量高低顺序为扁蓿豆 (Melilotoides ruthenica) >冷蒿 (Artemisia frigida) >羊草 (L eymus chinensis) >糙隐子草 (Cleistogenessquarrosa) ,反映了共有种群水分状况的不同。2质膜相对透性、游离脯氨酸含量均呈上升趋势 ,其中羊草、糙隐子草和冷蒿变化表现出先升后降再升的规律。3MDA含量变化均表现出先升后降再升的规律 ,不同植物不同阶段 MDA积累程度 (积累率大小顺序为沙漠化初期 :冷蒿 2 9.5 9% >羊草 18.14 % >扁蓿豆 13.6 8% >糙隐子草 3.77% ;沙漠化后期 :糙隐子草 80 .11% >冷蒿 77.2 9% >羊草 39.31% >扁蓿豆 8.5 6 % )的不同反映了不同阶段细胞受伤害程度的差异。4 SOD、CAT活性变化总体上均呈上升趋势 ,其中羊草 CAT活性呈降低趋势 ;酶活性均梯度间差异显著 (P<0 .0 0 1)。 5内源激素 ABA含量的变化因不同种群抗逆性强弱而异。糙隐子草、冷蒿和扁蓿豆 ABA增幅小 ,而羊草 ABA增幅大。综合各种生理特征及其对沙漠化环境的响应 ,对共有种群分类 :羊草为敏感型