A proteomic analysis of bacterial strain<Emphasis Type="Italic">Sinorhizobium fredii</Emphasis> RT19 subjected to salt shock

Sinorhizobium fredii RT19, a strain of freeliving bacteria, was subjected to salt shock and its protein expression profiles were analyzed by differential display proteome approaches. The results of separation by two-dimensional polyacrylamide gel electrophoresis (2D PAGE) showed that the number of resolved proteins was 481, 465 and 424, corresponding to salt-free control, 5 and 50 min 1 mol/L salt treatment, respectively. Among the resolved proteins, 82 in total had altered expression in response to salt-shock stress. 26 out of the 82 proteins were induced and 23 were completely inhibited, while 12 were up-regulated and 21 down-regulated in response to salt shock. In addition, the appearance of differentially displayed proteins responding to different salt shock periods is also reported. The identity of the 26 induced proteins was revealed by matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF/MS) followed by database searching. Among them, 20 were assigned to proteins with known functions. Their roles in response to salt shock stress are discussed.     

The induction of Sinorhizobium meliloti C4-dicarboxylate transport system （Dct） is regulated by oxygen concentration

The Sinorhizobium meliloti C4-dicarboxylate transport （Dct） system is essential for symbiotic nitrogen fixation. The dctA gene, encoding the C4-dicarboxylate permease, is expressed in both free living and symbiotic cells. But in free living cells expression of dctD and dctB is absolutely required for the expression of dctA. In this study, in order to investigate the effect of oxygen concentration on the induction of Dct system, E. coli DH5a strain which carries the plasmid-encoded dctABD operon was used in tube assays. It was found that the specific induction of Dct system oc- curred only at a certain depth under the surface of M63-0.6% agar media, suggesting that Dct system could respond to oxygen concentration during succinate-induced expression. Furthermore, when measured at different oxygen concentrations, the highest expression level was observed at oxygen concentration of 2%. Thus, we predict that in addition to dicarboxylates, the induction of Dct system may also regulated by oxygen concentration.     

费氏中华根瘤菌042BS(Rhizobium fredii 042BS)蛋白质组学初步研究

为了从蛋白质水平阐明根瘤菌的固氮机理,扩大其宿主植物范围,应用蛋白质组学技术(2-DE),分析比较了能够在大豆和苜蓿上跨宿主结瘤的费氏中华根瘤菌042BS与已经完成基因组测序的根瘤菌模式菌株苜蓿中华根瘤菌(Rhizobium meliloti 1021)的蛋白质表达图谱差异。经过图像分析检测到二者分别有436和428蛋白点。其中约有50个蛋白点初步认为二者所共有的。     

Extra-copy nifA enhances the nodulation efficiency of Sinorhizobium fredii

Previous investigations have shown that nifA gene is involved in nodulation and symbiotic nitrogen fixation regulation of Rhizobium. We study the role of nifA on nodulation of leguminous plants. We found that Sinorhizobium fredii harboring multi-copy plasmid carrying the constitutively expressed Klebsiella pneumoniae nifA exhibited an increase of noduiation activity and nodulation competitiveness on soybean plants. The Nod-factor secreted by the rhizobia cells containing the multi-copied nifA was assayed,and preliminary results showed that S. fredii containing the multi-copy plasmid carrying nifA produced higher strength of Nod-factor than the rhizobia containing the same plasmid carrying the vector did.     

Exogenous cAMP upregulates the expression of glnII and glnK-amtB genes in Sinorhizobium meliloti 1021

Sinorhizobium meliloti is a soil-borne bacterium that can lead a symbiosis life with leguminous host plants. Successful symbiont establishment requires specific recognition and progressive differentiation of both bac- teria and host cells. Once inside the plant cells of root nodules, the bacteria differentiate into non-dividing cells called bacteroids. Bacteroids obtain carbon source from the plant and, in return, they provide the plant with ammonium, and/or amino acid, as fixed nitrogen. Sign…     

外源nfeC基因导入快生型大豆根瘤菌菌株HN01的行为分析

ｎｆｃＣ基因是从慢生型大豆根瘤菌中克隆到的，与竞争结有关的基因。     

Isolation and characterization of a <Emphasis Type="Italic">Sinorhizobium fredii</Emphasis> mutant that cannot utilize proline as the sole carbon and nitrogen source

Sinorhizobium fredii strain HN01 can use proline as the sole carbon and nitrogen source. A mutant strain GXHN100 unable to catabolize proline was screened from 6000 Tn5gusA5 random insertional mutants of S.fredii strain HN01. Sequencing analysis showed that an open reading frame, named pmrA (proline metabolic relative), was inserted by the Tn5gusA5. A positive clone, namedp GXHN100 which containing 3.3kb foreign DNA fragment of S.fredii strain HN01, was isolated from a partial gene library of S.fredii HN01 by colony in situ hybridization. Sequence analysis showed that pGXHN100 contained the entire pmrA gene. The 3.3kb DNA fragment of pGXHN100 was cloned into a broad-host-range cosmid vector pLAFR3 to form plasmid pGXHN200 which was subsequently introduced into GXHN100 to form a complemented strain GXHN200. Plant test showed that GXHN100 was effective and no obvious changes in nitrogenase activity comparing with parental strain. But GXHN100 nodulated 2 days later on soybean and its nodulation efficiency and competitiveness were decreased.The complemented strain GXHN200 restored the nodulation efficiency and competitiveness of GXHN100 to the wild type.     

Identification of genes induced during Medicago sativa nodule development by using the cDNA-AFLP technique

Under limited nitrogen conditions, rhizobia are ableto induce the formation of nitrogen-fixing root nodules on their leguminous plant host. This organogenetic process is triggered by a complex exchange of molecu- lar signals between the host plant and bac…