苜蓿根瘤菌菌剂的研究

根据新疆气候特点,筛选出一株在耐旱、耐盐碱方面抗性较强的苜蓿根瘤菌Rhizobium sp.XJ67,并对其发酵条件及菌剂保存条件进行研究,结果表明该菌最适生长温度为30℃,最适pH为6.8,发酵液活菌数达19 300×108,菌剂最佳保存条件为冻干剂.     

导入dctABD和nifa基因对苜蓿中华根瘤菌共生固氮效率的影响

将克隆有四碳二羧酸转移酶基因dctABD、nifA基因和发光酶基因luxAB的重组质粒pHN307经三亲本杂交分别导入苜蓿根瘤菌HNM1、HNM2、HNM4和1021中得到HNM1（pHN307）等4个转移接合子，进一步比较研究了pHN307在自生培养条件下传代的稳定性，并采用本室改进的双层钵无菌砂培盆栽法，分别将4个转移接合子和出发菌接种到苜蓿品种草原1号，公农1号和图牧2号结果表明．只有用转移接合子HNM4（pHN307）和1021（pHN307）接种到草原1号和图牧2号的植株鲜重和干重明显优于出发菌     

苜蓿中华根瘤菌电转条件的优化

为了研究苜蓿中华根瘤菌电转化的条件,通过对不同的细胞生长周期、复苏缓冲液、电转缓冲液、电场强度和电阻对电转率影响程度来作出变化曲线,以确定电转化的最优条件,从而提高苜蓿中华根瘤菌电转化率.结果表明细胞的对数生长初期、复苏缓冲液Ⅴ、电转缓冲液Ⅳ、23 kv/cm和200Ω适合作为苜蓿中华根瘤菌电转的条件.     

Nodulation and growth of common bean (Phaseolus vulgaris) under water deficiency

Three experiments were conducted in order to investigate the effect of water deficiency on nodulation, rhizobial diversity and growth of common bean. In the first experiment, the effect of water deficiency was studied on two soil samples under glasshouse conditions. A significant decrease in nodulation and shoot dry weight production was observed. The molecular characterization of the root nodule isolates by PCR-RFLP of 16S rRNA and nodC genes showed that the nodulation by Rhizobium etli was severely inhibited. The in vitro analysis of salt tolerance indicated that drought stress favoured nodulation by salt-tolerant strains. In the second experiment, the effect of water deficiency was studied on sterilized sand using Rhizobium tropici CIAT899^T and Ensifer meliloti bv. mediterranense 4H41 as inoculants. The results showed that strain 4H41, which is the more salt tolerant, was more competitive and more effective under water deficiency than strain CIAT899^T. In the third experiment, the strain 4H41 was used to inoculate four fields. A significant increase in nodule number, shoot dry weight and grain yield was observed even in the non-irrigated soils. This work constitutes the first report of a strain enhancing the growth and the grain yield of common bean under water deficiency.     

Ecological pre-release risk assessment of two genetically engineered, bioluminescent Rhizobium meliloti strains in soil column model systems

In order to identify potential ecological risks associated with the environmental release of two Rhizobium meliloti strains, genetically engineered with the firefly-derived luciferase gene (luc), a pre-release greenhouse investigation was conducted. The upper 4 cm of soil columns (30 cm diameter; 65 cm depth), which were filled according to the horizons of an agricultural field (loamy sand), were inoculated with seeds of Medicago sativa (alfalfa) and R. meliloti cells at approximately 5×10⁶ cells·g^–1 soil. Four treatments were tested: inoculation with a non-engineered wild type strain (2011), strain L33 (luc ⁺), strain L1(luc ⁺, recA^–) and non-inoculated controls. The fate of the engineered strains was followed by two methods: (1) selective cultivation and subsequent detection of bioluminescent colonies and (2) PCR detection of the luc gene in DNA, directly extracted from soil. Strain R. meliloti L33 declined to 9.0×10⁴ cfu·g^–1 soil within 24 weeks and to 2.8×10³ cfu·g^–1 soil within 85 weeks in the upper 25 cm of the soil columns. Decline rates for R. meliloti L1 were not significantly different. Vertical distribution analysis of the recombinant cells after 37 weeks revealed that in three of four columns tested, the majority of cells (>98%) remained above 10 cm soil depth and no recombinant cells occurred below 20 cm depth. However, in one column all horizons below 20 cm were colonized with 2.2×10⁴ to 6.8×10⁴ cfu g^–1 soil. Ecological monitoring parameters included organic substance, total nitrogen, ammonium and nitrate, microbial biomass, culturable bacteria on four different growth media and the immediate utilization of 95 carbon sources (BiologGN) by soil-extracted microbial consortia. None of the parameters was specifically affected by the genetically engineered cells. Received: 6 December 1996     

Distribution and genetic diversity of rhizobia nodulating natural populations of Medicago truncatula in tunisian soils

A collection of 299 isolates of rhizobia nodulating Medicago truncatula was isolated from 10 Tunisian soils and was characterized by restriction fragment length polymorphism analysis of polymerase chain reaction (PCR/RFLP) of 16S rRNA gene. Results showed that 227 and 72 isolates were assigned, respectively, to Sinorhizobium meliloti and Sinorhizobium medicae. In 9 out of 10 soils S. meliloti was detected, whereas S. medicae was recovered from only 5 out of 10 soils. The cross-nodulation of three populations of M. truncatula grown on Bulla Regia soil, which contained naturally the two Sinorhizobium species, showed that M. truncatula population collected from Amra site was selective to S. meliloti at least in soil conditions. Forty-eight isolates of each Sinorhizobium species trapped by M. truncatula populations collected from Bulla Regia, Soliman and Rhayet sites on Bulla Regia soil were characterized by repetitive extragenic palindromic-PCR (REP-PCR) and showed a clear distinction between the two Sinorhizobium species and a higher diversity for S. meliloti.     

Genetic Variation in Alfalfa, Sweet Clover and Fenugreek for the Activity of Symbiosis with Rhizobium meliloti

The aim of this work was to examine variation for activity of symbiosis with Rhizobium meliloti in alfalfa, sweet clover and fenugreek. Seed specimens were obtained from the collection of the All-Union Research Institute for Plant Breeding and Rhizobium strains from the All-Union Research Institute for Agricultural Microbiology, both in Leningrad. Sterile methods of vegetative culture were employed. Statistical analysis of data on inter- and intracultivar variation allow one to suppose that in alfalfa and sweet clover, nitrogenase activity and symbiotic efficiency (ability of plants to increase biomass after inoculation) are controlled by different groups of genes. The latter symbiotic property is more strictly controlled by host genotype than the former. Fenugreek appeared to be more variable in its capacity for symbiosis than alfalfa and sweet clover. Differences between genotyyes in symbiotic activity correlate with division into subspecies and are inherited in self-fertile progeny of fenugreek plants. Differences between R. meliloti strains for the efficiency of symbiosis with heterogceic natural fenugreek population are expressed to a lesser degree than with plants of more homogenic cultivar populations.     

中华苜蓿根瘤菌被种子分泌物诱导的基因筛选和分析

土壤中的根瘤菌与宿主植物的共生结瘤过程中,豆科植物可以通过分泌氨基酸,有机酸,糖类,有机酚及其他的次级代谢产物的种类及丰度来影响根圈范围内微生物的群体种类及数量。豆科植物可以通过分泌趋化性物质如糖蛋白等协助根瘤菌吸附在合适的侵染位点,从而增加自身被感     

荒漠草原区苜蓿根瘤菌接种与冰草混播效果试验研究

对中华根瘤菌在苜蓿上接种,与蒙古冰草进行混合播种试验,并在形态、产量、营养品质等方面作了比较分析,探讨苜蓿与禾本科牧草混作后的增产效益。结果表明,苜蓿接种根瘤菌处理后混播较不接种根瘤菌、施氮肥和不接种根瘤菌、不施氮肥处理的牧草产量分别提高33.91%和64.89%,提高了群体草地利用效益,混播既便于牧草贮藏与利用,又可提高牧草的饲用价值,能够获得较好的经济效益。     

中华根瘤菌NL的筛选与鉴定

从吉林某菜园土样中筛选到菌株NL,用该菌对伊利石进行浸矿脱硅试验,测得接种NL的溶液中的可溶性硅的浓度比对照液中的增67.83%,说明该菌能促进伊利石中硅的溶解.从菌株NL的培养特征、形态大小、生理生化测试和16S rDNA序列的比对分析等方面进行了鉴定,其16S rDNA序列与GenBank中的中华根瘤菌属Sinorhizobium sp.S1-5(AY505134)的相似性达99.62%.试验结果表明菌株NL属于中华根瘤菌(Sinorhizobium).