一种根瘤菌胞外多糖对小鼠免疫功能的影响

目的研究一种根瘤菌胞外多糖(REPS)对正常小鼠免疫功能的影响。方法将该多糖以大、中、小3个剂量[(40、20、10 mg/(Kg.d)]给小鼠连续腹腔注射(ip)10 d,测定胸腺质量、脾脏质量、碳粒廓清指数、血清抗绵羊红细胞(SRBC)抗体凝集效价和淋巴细胞转化值。结果与对照组比较,该多糖使小鼠脾脏质量明显增加,单核吞噬细胞的吞噬能力显著增强,提高了血清抗SRBC抗体凝集效价,增强了小鼠脾淋巴细胞转化功能。结论此根瘤菌胞外多糖对小鼠的非特异性和特异性免疫功能均有明显的增强作用。     

根癌农杆菌介导的尿嘧啶缺陷烟曲霉转化是基因敲除的有效方法

目的:探讨用嘧啶营养缺陷作为筛选标记、根癌农杆菌介导的转化方法敲除烟曲霉基因.方法:以pyrG作为筛选标记,在双元载体pDHt/sk上分别构建烟曲霉FAPI,和SHOI基因的打靶序列.构建好的质粒分别转化入根癌农杆菌.24℃条件下,含打靶质粒的根癌农杆菌与烟曲霉在不含尿嘧啶和尿苷的诱导培养基上共培养48h;然后将培养物转移到37℃,筛选转化子.结果:根癌农杆菌介导的烟曲霉转化同源重组率较高,FAPI基因为44%(7/16)、SHOI基因为35%(7/20).结论:以pyrG作为筛选标记、根癌农杆菌介导的转化方法能高效敲除烟曲霉基因,为烟曲霉基因功能研究提供了有效方法.     

Protective Role of Native Rhizospheric Soil Microbiota Against the Exposure to Microcystins Introduced into Soil-Plant System via Contaminated Irrigation Water and Health Risk Assessment

Microcystins (MCs) produced in eutrophic waters may decrease crop yield, enter food chains and threaten human and animal health. The main objective of this research was to highlight the role of rhizospheric soil microbiota to protect faba bean plants from MCs toxicity after chronic exposure. Faba bean seedlings were grown in pots containing agricultural soil, during 1 month under natural environmental conditions of Marrakech city in Morocco (March–April 2018) and exposed to cyanobacterial extracts containing up to 2.5 mg·L⁻¹ of total MCs. Three independent exposure experiments were performed (a) agricultural soil was maintained intact “exposure experiment 1”; (b) agricultural soil was sterilized “exposure experiment 2”; (c) agricultural soil was sterilized and inoculated with the rhizobia strain Rhizobium leguminosarum RhOF34 “exposure experiment 3”. Overall, data showed evidence of an increased sensitivity of faba bean plants, grown in sterilized soil, to MCs in comparison to those grown in intact and inoculated soils. The study revealed the growth inhibition of plant shoots in both exposure experiments 2 and 3 when treated with 2.5 mg·L⁻¹ of MCs. The results also showed that the estimated daily intake (EDI) of MCs, in sterilized soil, exceeded 2.18 and 1.16 times the reference concentrations (0.04 and 0.45 µg of microcysin-leucine arginine (MC-LR). Kg⁻¹ DW) established for humans and cattle respectively, which raises concerns about human food chain contamination.     

Analysis of Rhizobium etli and of its symbiosis with wild Phaseolus vulgaris supports coevolution in centers of host diversification

Common beans (Phaseolus vulgaris) comprise three major geographic genetic pools, one in Mexico, Central America, and Colombia, another in the southern Andes, and a third in Ecuador and northern Peru. Species Rhizobium etli is the predominant rhizobia found symbiotically associated with beans in the Americas. We have found polymorphism in the common nodulation gene nodC among R. etli strains from a wide range of geographical origins, which disclosed three nodC types. The different nodC alleles in American strains show varying predominance in their regional distributions in correlation with the centers of bean genetic diversification (BD centers). By cross-inoculating wild common beans from the three BD centers with soils from Mexico, Ecuador, Bolivia, and Northwestern Argentina, the R. etli populations from nodules originated from Mexican soil again showed allele predominance that was opposite to those originated from Bolivian and Argentinean soil, whereas populations from Ecuadorian soil were intermediate. These results also indicated that the preferential nodulation of beans by geographically related R. etli lineages was independent of the nodulating environment. Coinoculation of wild common beans from each of the three BD centers with an equicellular mixture of R. etli strains representative of the Mesoamerican and southern Andean lineages revealed a host-dependent distinct competitiveness: beans from the Mesoamerican genetic pool were almost exclusively nodulated by strains from their host region, whereas nodules of beans from the southern Andes were largely occupied by the geographically cognate R. etli lineages. These results suggest coevolution in the centers of host genetic diversification.     

患儿导管相关性放射根瘤菌血流感染实验室诊断方法探讨

目的探讨患儿导管相关性放射根瘤菌血流感染的诊断方法和感染因素。方法收集某院2012年2月—2014年2月1 014例使用各类中心静脉导管的患儿资料,检测放射根瘤菌感染患儿导管半定量培养,导管与静脉血菌落数比,以及静脉血与导管培养时间差;分析放射根瘤菌感染危险因素。结果 1 014例使用各类中心静脉导管的患儿,导管和静脉血标本分别培养出放射根瘤菌32例和28例,27例患儿导管血和静脉血均为阳性。导管半定量培养菌落数≥15 CFU者27例,15 CFU者5例;导管与静脉血菌落数比≥5∶1者22例,5∶1者6例;静脉血与导管培养时间差≥2 h者26例,2 h者2例。危险因素分析结果显示,患儿年龄、导管留置时间各组比较差异有统计学意义(均P0.05)。结论导管半定量培养、导管与静脉血菌落数比值及静脉与导管血培养时间差均是判断导管相关性放射根瘤菌血流感染的重要诊断依据;患儿年龄2岁、导管留置时间5 d是导管相关性放射根瘤菌血流感染的危险因素。     

Tsukamurella tyrosinosolvens and Rhizobium radiobacter sepsis presenting with septic pulmonary emboli

Septic pulmonary embolism (SPE) is an uncommon, but life-threatening event that is usually associated with extrapulmonary infections. We report the first case of bilateral SPE secondary to a central venous catheter-related bloodstream infection involving pathogens commonly considered environmental contaminants: Tsukamurella tyrosinosolvens and Rhizobium radiobacter. Empirical levofloxacin treatment was confirmed by in vitro susceptibility data and produced prompt clinical improvement, but removal of the infected line proved indispensable for eradication of the infection. Laboratory personnel should be aware of the pathogenic potential of these environmental organisms, particularly in immunocompromised hosts with indwelling catheters.     

Iraq's Biological Warfare Agents: A Comprehensive Analysis

The leguminous crop Arachis hypogaea L. (peanut) is originally from South America and then was disseminated to tropical and subtropical regions. The dissemination of the crop resulted in peanut plants establishing a symbiotic nitrogen-fixing relationship with a wide diversity of indigenous soil bacteria. We present in this review, advances on the molecular basis for the crack-entry infection process involved in the peanut-rhizobia interaction, the diversity of rhizobial and fungal antagonistic bacteria associated with peanut plants, the effect of abiotic and biotic stresses on this interaction and the response of peanut to inoculation.