Dextranase from Arthrobacter oxydans KQ11-1 inhibits biofilm formation by polysaccharide hydrolysis

Dental plaque is a biofilm of water-soluble and water-insoluble polysaccharides, produced primarily by Streptococcus mutans. Dextranase can inhibit biofilm formation. Here, a dextranase gene from the marine microorganism Arthrobacter oxydans KQ11-1 is described, and cloned and expressed using E. coli DH5α competent cells. The recombinant enzyme was then purified and its properties were characterized. The optimal temperature and pH were determined to be 60°C and 6.5, respectively. High-performance liquid chromatography data show that the final hydrolysis products were glucose, maltose, maltotriose, and maltotetraose. Thus, dextranase can inhibit the adhesive ability of S. mutans. The minimum biofilm inhibition and reduction concentrations (MBIC₅₀ and MBRC₅₀) of dextranase were 2 U ml^?1 and 5 U ml^?1, respectively. Scanning electron microscopy and confocal laser scanning microscope (CLSM) observations confirmed that dextranase inhibited biofilm formation and removed previously formed biofilms.     

Cloning,expression, and purification of an antiviral protein from Pseudomonas fluorescens CZ and its antagonistic activity against tobacco mosaic virus

The antiviral alkaline phosphatase L (AapL) protein of Pseudomonas fluorescens CZ was expressed in Escherichia coli, purified using the Ni-NTA column, and its antiviral activity against tobacco mosaic virus (TMV)-infected Nicotiana was tested. The recombinant protein (360?µg/mL) showed stability and most effective suppression in vitro (94.85%) against TMV.     

Structural Modification of Stilbenoids from Acanthopanax leucorrhizus and Their Cytotoxic Activity

A new cis‐stilbenoid, 1,9‐dihydroxy‐10‐methoxy‐6H‐dibenzo[b,f]oxocin‐6‐one ( 2 ) was isolated from the AcOEt extract of the stem barks of Acanthopanax leucorrhizus, along with three known stilbenoids, 9‐hydroxy‐10‐methoxy‐6H‐dibenzo[b,f]oxocin‐6‐one ( 1 ), 5‐O‐methyl‐(E)‐resveratrol 3‐O‐β‐d ‐glucopyranoside ( 3 ), and (E)‐resveratrol 3‐O‐β‐d ‐xylopyranoside ( 4 ). Two derivatives ( 2a and 2b ) were synthesized by the structural modification of compound 2, which exhibited certain cytotoxic activities against HT‐29 and HeLa cell lines in vitro. All compounds were structurally characterized by comprehensive analysis of their spectroscopic data and comparison with literature information, and evaluated for their cytotoxic activities against three human tumor cell lines (HL‐60, HT‐29, and HeLa) by the standard MTT assay in vitro. The results showed that derivatives 2a and 2b exhibited strong activities than compounds 2 against HT‐29 and HeLa cell lines.     

Photosynthetic characteristics and effect of ATP in transgenic rice with phospho<Emphasis Type="Italic">enol</Emphasis>pyruvate carboxylase and pyruvate orthophosphate dikinase genes

In the untransformed rice (WT) and transgenic rice with the PEPC and PPDK genes (CK) we determined activities of C₄ photosynthetic enzymes, photosynthetic response to irradiance and temperature, the metabolic index of active oxygen, and the yield component factors. The activities of C₄ photosynthetic enzymes in WT were very low, while those of corresponding enzymes in CK were highly observable. Moreover, after adenosine triphosphate (ATP) treatment, and under high irradiance and high temperature, the net photosynthetic rate of CK increased by 17 and 12 %, respectively, as compared to that achieved without ATP treatment. The resistance of CK against photo-oxidation was enhanced under these conditions, and CK yield increased by 15 %. ATP treatment enhanced the photosynthetic productivity of CK, thereby proving that ATP is the key factor in enhancing the photosynthetic capacity of transgenic rice with C₄ gene. Our new technical approach can be used in breeding rice with high photosynthetic efficiency and high grain yield.     

The Evolutionary Divergence of psbA Gene in Synechococcus and Their Myoviruses in the East China Sea

Marine Synechococcus is a principal component of the picophytoplankton and makes an important contribution to primary productivity in the ocean. Synechophages, infecting Synechococcus, are believed to have significant influences on the distribution and abundance of their hosts. Extensive previous ecological studies on cyanobacteria and viruses have been carried out in the East China Sea (ECS). Here we investigate the diversity and divergence of Synechococcus and their myoviruses (Synechomyoviruses) based on their shared photosynthesis psbA gene. Synechococcus is dominated by subclades 5.1A I, 5.1A II and 5.1A IV in the ECS, and clades I and II are the dominant groups in the Synechomyoviruses. As two phylogenetically independent clades, there is much higher diversity of the Synechomyoviruses than Synechococcus. Obvious partitioning characteristics of GC and GC3 (the GC content at the third codon position) contents are obtained among different picophytoplankton populations and their phages. The GC3 content causes the psbA gene in Synechococcus to have a higher GC content, while the opposite is true in the Synechomyoviruses. Analyzing more than one-time difference of the codon usage frequency of psbA sequences, the third position nucleotides of preferred codons for Synechococcus are all G and C, while most Synechomyoviral sequences (72.7%) have A and T at the third position of their preferred codons. This work shed light on the ecology and evolution of phage-host interactions in the environment.     

拟南芥转录因子GRAS 家族基因群响应渗透和干旱胁迫的初步探索

GRAS家族是一类植物特有的转录调控因子, 已有报道表明该家族基因在植物生长发育和光信号转导过程中具有重要作用。目前在拟南芥(Arabidopsis thaliana)基因组中已鉴定了33个GRAS家族基因。利用功能基因组学和生物信息学手段,通过基因芯片数据挖掘和基因功能预测, 对拟南芥GRAS家族基因在渗透和干旱胁迫过程中的应答模式进行了初步探索, 提出了一类响应渗透胁迫和干旱胁迫的拟南芥GRAS家族基因。以SCL13为例, 利用基因芯片相关性和GO分析, 对其在渗透胁迫信号转导过程中可能的调控机制进行了预测和分析。这一研究将为阐明GRAS家族基因参与水分胁迫的分子机制提供新的思路, 同时也为植物抗逆分子育种提供候选基因。     

一株红球菌(Rhodococcus sp.)二噁英降解质粒的稳定性与接合转移特性

【目的】考察一株红球菌Rhodococcus sp.strain p52中的二噁英降解质粒pDF01(170 kb)和pDF02(242 kb)的稳定性和接合转移特性。【方法】在无选择压力的条件下对菌株p52进行连续传代培养,考察质粒pDF01、pDF02的丢失;以菌株p52为供体菌,以不同种属的菌株作受体菌,通过平板接合实验探讨质粒pDF01、pDF02接合转移的受体菌范围以及接合转移频率,利用菌落杂交、Southern杂交对质粒转移结果进行确认,利用降解实验测试转移质粒降解基因的表达。【结果】质粒pDF01和pDF02在红球菌p52中均具有较高的稳定性,在LB培养基上连续传代少于47次时pDF02可保持,连续传代少于65次时pDF01可保持。质粒pDF01和pDF02具备在同属和属间接合转移的能力,可向受体菌——紫红红球菌(Rhodococcus rhodochrous)、红串红球菌(Rhodococcus erythropolis)、大地两面神菌(Terrabacter tumescens)和节杆菌(Arthrobacter sp.)转移,其中以节杆菌作受体菌时质粒pDF01和pDF02接合转移频率最高,达到3.5×10~(-6)(接合子/受体菌);对节杆菌接合子质粒进行Southern杂交进一步确认了质粒pDF01、pDF02的存在。另外获得质粒pDF01、pDF02后的节杆菌接合子可以对二苯并呋喃高效利用,且降解能力与红球菌供体菌株p52相当。【结论】红球菌菌株p52可通过降解质粒转移强化生物修复过程,在去除环境中二噁英污染中具有良好的应用前景。