Novel Rhizobium lineages isolated from root nodules of the common bean (Phaseolus vulgaris L.) in Andean and Mesoamerican areas

The taxonomic affiliations of nineteen root-nodule bacteria isolated from the common bean (Phaseolus vulgaris L.) in Mexico, Ecuador and Brazil were investigated by analyses of 16S rRNA and of four protein-coding housekeeping genes. One strain from Mexico could be assigned to Rhizobium etli and two from Brazil to Rhizobium leucaenae, whereas another from Mexico corresponded to a recently described bean-nodulating species-level lineage related to R. etli and Rhizobium phaseoli. Ten strains isolated in Ecuador and Mexico corresponded to three novel Rhizobium lineages that fall into the R. phaseoli/R. etli/Rhizobium leguminosarum clade. One of those lineages, with representatives isolated mostly from Ecuador, seems to be dominant in beans from that Andean region. Only one of the Mexican strains clustered within the Rhizobium tropici clade, but as an independent lineage. Interestingly, four strains were affiliated with species within the Rhizobium radiobacter clade. The existence of yet non-described native Rhizobium lineages in both the Andean and Mesoamerican areas is discussed in relation to common-bean diversity and environmental conditions.     

Effects of removing symbiotic green algae on the response of Hydra viridissima (Pallas 1776) to metals

Hydra viridissima is distinctively green due to symbiotic algae within the endodermal cells. The current investigation was designed to see if these algae influenced the response of Hydra to pollutants, by comparing the toxicity of copper, cadmium, and zinc to both symbiotic and aposymbiotic (free of their endosymbiotic algae) H. viridissima. The results demonstrated that the toxicity of the metals was generally similar for both groups of Hydra. However, at the lowest copper concentrations there was a difference between the two group of polyps, with aposymbiotic animals dying at concentrations where symbiotic Hydra survived. The lowest observed effect concentrations were 0.0068 and 0.016 mg/L for aposymbiotic and symbiotic Hydra, respectively. It is suggested that the symbiotic Hydra derive benefits from the association that enable them to better tolerate the toxicant. This work demonstrated that experimental manipulation of symbionts can help to explain their complex interactions and the ways in which they respond to pollutants.     

Chemical biology of the mutualistic relationships of sea anemones with fish and crustaceans

Fish species of the genera Amphiprion and Premnas (Perciformes: Pomacentridae) as well as various crustaceans seek protection from predators among the tentacles of sea anemones, where they live essentially unharmed from stinging by the host's nematocysts. The mucous coats of anemonefish and crustaceans have been suggested as mechanisms that prevent the discharge of the nematocysts upon contact. Whereas some fish species seem to produce their own protecting mucous coating, others may acquire mucus from the sea anemone during an acclimation period, as crustaceans do. Whether the natural or acquired mucus layers contain components that inhibit nematocyst discharge or simply lack compounds stimulating the stinging cell's exocytosis is still unknown.     

Evolutionary Origin of Eukaryotic Cells

This article reviews literature on the transition from rudimentary prokaryotic life to eukaryotes. An overview of the differences between these organisms and theories of eukaryogenesis are reviewed. Various methods of investigating the transformation from prokaryotes to eukaryotes are elaborated, including the fossil, the molecular and living records, and examples are given. Lastly, the recent molecular studies and the impact on phylogenetic classification for the tree of life, based on molecular evolution, are discussed.     

成年大鼠联体诱导的移植耐受与嵌合状态相关性的研究

目的 将异基因成年大鼠联体共生（ｐａｒａｂｉｏｓｉｓ）以诱导相互特异的移植耐受，探讨嵌合体与耐受的关系。方法 联体前后低剂量环磷酰胺（ＣＰ，１００ｍｇ／ｋｇ）腹腔注射，观察联体大鼠存活时间。分别于联体５、１５、４５ｄ时将联体大鼠分开，并相互植皮，观察皮肤存活情况，并在上述时间点以流式细胞仪检测联体分开后大鼠胸腺、脾脏中供体来源细胞的嵌合状态。在联体１５ｄ时检测同种异型混合淋巴细胞反应（ＭＬＲ）、迟     

1至4个月龄正常婴幼儿结膜囊菌群分布特征分析

目的 探讨1至4个月龄正常婴幼儿结膜囊的菌群分布及其相关影响因素.方法 横断面研究方法.2009年1至3月天津医科大学眼科中心与天津市妇女儿童保健中心合作,采取简单随机抽样研究方法选择109例接受眼病筛查的1至4个月龄的健康小儿,进行双眼结膜囊分泌物取材并做细菌培养和鉴定.应用卡方检验、t检验和回归分析方法对数据进行统计学处理,分析结膜囊细菌种类和分布以及相关影响因素.结果 结膜囊分泌物培养阳性的小儿26例(36只眼),占23.9%.共检出7种44株细菌,包括革兰阳性球菌25株,革兰阳性杆菌18株,革兰阴性杆菌1株.其中类白喉棒状杆菌17株(17/44,38.6%),表皮葡萄球菌16株(16/44,36.4%),金黄色葡萄球菌6株(6/44,13.6%).单眼分离出2种细菌者8只眼(8/36,22.2%),均为葡萄球菌和类白喉棒状杆菌.不同月龄、性别及喂养方式的细菌培养结果差异无统计学意义(X2=0.351,X2=0.001,X2=1.182,P值均大于0.05).结膜囊培养阳性者26例(36只眼),培养阴性者83例(166只眼),两组小儿的出生体重、胎龄及受检周龄比较差异无统计学意义(t=0.078,t=0.940,t=0.686,P值均大于0.05).本研究中性别、年龄、出生体重、胎龄及喂养方式不影响结膜囊带菌状态(Wald X2=0.001,Wald X2=0.003,Wald X2=0.117,Wald X2=1.307,Wald X2=1.490,P值均大于0.05).结论 婴儿期结膜囊正常菌群已经建立,以表皮葡萄球菌和类白喉棒状杆菌为主要菌种.葡萄球菌与类白喉棒状杆菌有共生现象.小儿结膜囊带菌状态相关影响因素仍需进一步研究.     

蚊虫的共生菌及其在媒介控制中的应用

许多昆虫与寄生在昆虫体表或肠道细胞中的微生物建立了共生关系。臭虫、蚜虫、猎蝽等昆虫可以依靠非最佳食物为生,这一是由于其特殊的生存环境,还由于其体内的共生微生物可以帮助合成和补充其食物中所缺乏的必需营养物质。蚊虫也与其肠道中共生细菌有着密切的联系。成蚊喜产卵于富舍细菌的水体中,水体细菌成为蚊虫幼虫的重要食物来源。伊蚊和库蚊幼虫正常生长发育不可缺少细菌,在无菌条件下饲养,蚊虫或其他媒介昆虫不能正常发育至成熟或不能传播人畜疾病。该文对蚊虫与细菌的共生现象以及其在以下几方面的应用进行综述,（1）蚊虫共生细菌的分离与鉴定,（2）共生细菌的形成与传代,（3）共生细菌在昆虫中的分布,并讨论了经过遗传改造的蚊虫共生细菌对蚊虫防治及控制疟疾等由昆虫传播的疾病的应用前景。     

Acanthamoeba castellanii supports extracellular survival of Helicobacter pylori in co-culture

This study aimed to demonstrate whether Helicobacter pylori is able to survive in co-culture with a protozoan, Acanthamoeba castellanii, in order to further investigate a possible aqueous environmental mode of transmission. Numbers of H. pylori in co-culture with A castellanii were assessed by colony forming unit (CFU) assay and cell morphology was observed by electron microscopy. Viable and intact H. pylori in co-culture were detected and the number of H. pylori in co-culture with A. castellanii was significantly higher than in bacterial single culture. It was also shown that co-culture of H. pylori with A. castellanii physically separated by a filter membrane negated this survival effect, suggesting that adherence of H. pylori to A. castellanii affects its survival. Scanning electron microscopy revealed helical forms of H. pylori in co-culture with A. castellanii, but not in single culture. These results imply that mutual interaction between H. pylori and A. castellanii in the environment is critical for survival of H. pylori. In addition, the H. pylori gene expression profile was found to differ between single and co-cultured cells using RNA-sequence analysis.     

Bacterial endosymbionts in field-collected samples of Trialeurodes sp. nr. abutiloneus (Hemiptera: Aleyrodidae)

Facultative bacterial endosymbionts are common, influential associates of arthropods, yet their movement among host species has not been well documented. Plant-mediated transmission of Rickettsia has been shown for the whitefly Bemisia tabaci. Bemisia tabaci in USA cotton fields harbors the secondary symbionts Rickettsia and Hamiltonella, and co-occurs with Trialeurodes sp. nr. abutiloneus whiteflies. To determine whether symbionts may be shared, the microbial diversity of these whiteflies on cotton across the USA was analyzed. Trialeurodes sp. nr. abutiloneus bore Portiera, Pseudomonas, Serratia, Arsenophonus and Wolbachia. No Rickettsia or Hamiltonella were detected. These results provide no evidence for horizontal transmission of symbionts between these whitefly genera.