Cell-to-cell transfer of bacterial outer membrane lipoproteins

Myxococcus xanthus cells can glide forward by retracting type IV pili. Tgl, an outer membrane lipoprotein, is necessary to assemble pili. Tgl mutants can be transiently "stimulated" if brought into end-to-end contact with tgl+ donor cells. By separating the stimulated recipient cells from donor cells, we found that Tgl protein was transferred from the donors to the rescued recipient cells. Mutants lacking CglB lipoprotein, which is part of a second gliding engine, could also be stimulated, and CglB protein was transferred from donor to recipient cells. The high transfer efficiency of Tgl and CglB proteins suggests that donor and recipient cells briefly fuse their outer membranes.     

Translocation of Helicobacter pylori CagA into gastric epithelial cells by type IV secretion

The Gram-negative bacterium Helicobacter pylori is a causative agent of gastritis and peptic ulcer disease in humans. Strains producing the CagA antigen (cagA(+)) induce strong gastric inflammation and are strongly associated with gastric adenocarcinoma and MALT lymphoma. We show here that such strains translocate the bacterial protein CagA into gastric epithelial cells by a type IV secretion system, encoded by the cag pathogenicity island. CagA is tyrosine-phosphorylated and induces changes in the tyrosine phosphorylation state of distinct cellular proteins. Modulation of host cells by bacterial protein translocation adds a new dimension to the chronic Helicobacter infection with yet unknown consequences.     

Generating and exploiting polarity in bacteria

Bacteria are often highly polarized, exhibiting specialized structures at or near the ends of the cell. Among such structures are actin-organizing centers, which mediate the movement of certain pathogenic bacteria within the cytoplasm of an animal host cell; organized arrays of membrane receptors, which govern chemosensory behavior in swimming bacteria; and asymmetrically positioned septa, which generate specialized progeny in differentiating bacteria. This polarization is orchestrated by complex and dynamic changes in the subcellular localization of signal transduction and cytoskeleton proteins as well as of specific regions of the chromosome. Recent work has provided information on how dynamic subcellular localization occurs and how it is exploited by the bacterial cell. The main task of a bacterial cell is to survive and duplicate itself. The bacterium must replicate its genetic material and divide at the correct site in the cell and at the correct time in the cell cycle with high precision. Each kind of bacterium also executes its own strategy to find nutrients in its habitat and to cope with conditions of stress from its environment. This involves moving toward food, adapting to environmental extremes, and, in many cases, entering and exploiting a eukaryotic host. These activities often involve processes that take place at or near the poles of the cell. Here we explore some of the schemes bacteria use to orchestrate dynamic changes at their poles and how these polar events execute cellular functions. In spite of their small size, bacteria have a remarkably complex internal organization and external architecture. Bacterial cells are inherently asymmetric, some more obviously so than others. The most easily recognized asymmetries involve surface structures, e.g., flagella, pili, and stalks that are preferentially assembled at one pole by many bacteria. "New" poles generated at the cell division plane differ from old poles from the previous round of cell division. Even in Escherichia coli, which is generally thought to be symmetrical, old poles are more static than new poles with respect to cell wall assembly (1), and they differ in the deposition of phospholipid domains (2). There are many instances of differential polar functions; among these is the preferential use of old poles when attaching to host cells as in the interaction of Bradyrhizobium with plant root hairs (3) or the polar pili-mediated attachment of the Pseudomonas aeruginosa pathogen to tracheal epithelia (4). An unusual polar organelle that mediates directed motility on solid surfaces is found in the nonpathogenic bacterium Myxococcus xanthus. The gliding motility of this bacterium is propelled by a nozzle-like structure that squirts a polysaccharide-containing slime from the pole of the cell (5). Interestingly, M. xanthus, which has nozzles at both poles, can reverse direction by closing one nozzle and opening the other in response to end-to-end interactions between cells.     

CD46 in meningococcal disease

The human-specific bacterial pathogen Neisseria meningitidis is a major cause of sepsis and/or meningitis. The pili of N. meningitidis interact with CD46, a human cell-surface protein involved in regulation of complement activation. Transgenic mice expressing human CD46 were susceptible to meningococcal disease, because bacteria crossed the blood-brain barrier in these mice. Development of disease was more efficient with piliated bacteria after intranasal, but not intraperitoneal, challenge of CD46 transgenic mice, suggesting that human CD46 facilitates pilus-dependent interactions at the epithelial mucosa. Hence, the human CD46 transgenic mice model is a potentially useful tool for studying pathogenesis and for vaccine development against meningococcal disease.     

嗜水气单胞菌J-1株粘附素及其受体分析

以EPC细胞和HEp-2细胞为细胞模型，用嗜水气单胞菌（Aeromonas hydrophila,Ah)J－1株进行粘附试验，同时以Ah4型菌毛的抗血清作粘附抑制试验，用以分析AhJ-1株的粘附素及其受体。EPC细胞粘附和粘附抑制试验证实，Ah J-1株粘附素受体具有甘露糖、胆固醇成分，有少量半乳糖成分，无葡萄糖成分。HEp-2细胞粘附和粘附抑制试验证实，与其它非菌毛粘附素如S层及外膜蛋白相比，Ah4型菌毛的粘附作用较为显。抗4型菌毛抗体和抑制细菌的粘附力达80％以上。抗S层、外膜蛋白抗体也能使细菌的粘附力下降，表明Ah的粘附作用由菌毛粘附素与非菌毛粘附素共同参与。     

Regulated pole-to-pole oscillations of a bacterial gliding motility protein

Little is known about directed motility of bacteria that move by type IV pilus-mediated (twitching) motility. Here, we found that during periodic cell reversals of Myxoccocus xanthus, type IV pili were disassembled at one pole and reassembled at the other pole. Accompanying these reversals, FrzS, a protein required for directed motility, moved in an oscillatory pattern between the cell poles. The frequency of the oscillations was controlled by the Frz chemosensory system, which is essential for directed motility. Pole-to-pole migration of FrzS appeared to involve movement along a filament running the length of the cell. FrzS dynamics may thus regulate cell polarity during directed motility.     

Stabilizing isopeptide bonds revealed in gram-positive bacterial pilus structure

Many bacterial pathogens have long, slender pili through which they adhere to host cells. The crystal structure of the major pilin subunit from the Gram-positive human pathogen Streptococcus pyogenes at 2.2 angstroms resolution reveals an extended structure comprising two all-beta domains. The molecules associate in columns through the crystal, with each carboxyl terminus adjacent to a conserved lysine of the next molecule. This lysine forms the isopeptide bonds that link the subunits in native pili, validating the relevance of the crystal assembly. Each subunit contains two lysine-asparagine isopeptide bonds generated by an intramolecular reaction, and we find evidence for similar isopeptide bonds in other cell surface proteins of Gram-positive bacteria. The present structure explains the strength and stability of such Gram-positive pili and could facilitate vaccine development.     

Evidence that focal adhesion complexes power bacterial gliding motility

The bacterium Myxococcus xanthus has two motility systems: S motility, which is powered by type IV pilus retraction, and A motility, which is powered by unknown mechanism(s). We found that A motility involved transient adhesion complexes that remained at fixed positions relative to the substratum as cells moved forward. Complexes assembled at leading cell poles and dispersed at the rear of the cells. When cells reversed direction, the A-motility clusters relocalized to the new leading poles together with S-motility proteins. The Frz chemosensory system coordinated the two motility systems. The dynamics of protein cluster localization suggest that intracellular motors and force transmission by dynamic focal adhesions can power bacterial motility.     

Plague bacteria target immune cells during infection

The plague is caused by the bacterium Yersinia pestis. Plague bacteria are thought to inject effector Yop proteins into host cells via the type III pathway. The identity of the host cells targeted for injection during plague infection is unknown. We found, using Yop beta-lactamase hybrids and fluorescent staining of live cells from plague-infected animals, that Y. pestis selected immune cells for injection. In vivo, dendritic cells, macrophages, and neutrophils were injected most frequently, whereas B and T lymphocytes were rarely selected. Thus, it appears that Y. pestis disables these cell populations to annihilate host immune responses during plague.     

Ankyrin repeat proteins comprise a diverse family of bacterial type IV effectors

Specialized secretion systems are used by many bacteria to deliver effector proteins into host cells that can either mimic or disrupt the function of eukaryotic factors. We found that the intracellular pathogens Legionella pneumophila and Coxiella burnetii use a type IV secretion system to deliver into eukaryotic cells a large number of different bacterial proteins containing ankyrin repeat homology domains called Anks. The L. pneumophila AnkX protein prevented microtubule-dependent vesicular transport to interfere with fusion of the L. pneumophila-containing vacuole with late endosomes after infection of macrophages, which demonstrates that Ank proteins have effector functions important for bacterial infection of eukaryotic host cells.     

Legionella effectors that promote nonlytic release from protozoa

Legionella pneumophila, the bacterial agent of legionnaires' disease, replicates intracellularly within a specialized vacuole of mammalian and protozoan host cells. Little is known about the specialized vacuole except that the Icm/Dot type IV secretion system is essential for its formation and maintenance. The Legionella genome database contains two open reading frames encoding polypeptides (LepA and LepB) with predicted coiled-coil regions and weak homology to SNAREs; these are delivered to host cells by an Icm/Dot-dependent mechanism. Analysis of mutant strains suggests that the Lep proteins may enable the Legionella to commandeer a protozoan exocytic pathway for dissemination of the pathogen.     

西北盐碱土主要植物丛枝菌根研究

对西北地区盐碱土主要植物的丛枝菌根真菌共生状况进行了调查与分析。结果表明,在14科29种植物中,除红砂(Reaumuria songarica Maxim.)外,其余植物均被菌根真菌侵染,侵染比例为96.55%;在过去认为不被侵染的莎草科(Cyperaceae)和藜科(Chenopodiaceae)植物中,发现寸草苔(Carex duriuscula C.A.Mey.)、筛草(Carex kobomugi Ohwi)、盐角草(Saliconia europaea L.)、碱蓬(Suaeda glauca Beg.)和盐爪爪(Kalidium foliatumMoq.)有侵染现象;所调查的乔木和草本类植物的菌根植物比例为100%,灌木植物为87.50%;丛枝菌根结构类型以A型为主,占65.52%,P型占27.59%;菌根侵染率和侵染强度与植物的种类、生活型、根系类型及土壤含水量的关系密切;菌根结构类型主要受植物种类及其根系类型的影响,与土壤含水量和植物的生活型无关。     

3个血清型鸡源大肠杆菌1型菌毛蛋白抗原位点变异分析

采用Goldkey及DNA Star分析软件对发表的3个不同血清型的鸡大肠杆菌1型菌毛结构基因(pilA)进行同源性及抗原位点分析。结果显示,3种鸡大肠杆菌(O_1、O_(78)及O_(88))l型菌毛pilA基因相似性为91.36％～98.38％,所编码的氨基酸同源性为93.50％～97.84％;3种血清型鸡大肠杆菌(O_1、O_(78)及O_(88))1型菌毛蛋白二级结构在1～73位及150～185位氨基酸的二级结构基本相似,而111～150位氨基酸的α螺旋与β折叠的数量有所不同。菌毛蛋白亲水性、抗原性及抗原决定簇预测表明,来源于3种血清型大肠杆菌的1型菌毛蛋白在l～110位及150～184位氨基酸存在相似的二级结构及抗原位点,且不同血清型之间存在一定的共同抗原。     

肠出血性大肠杆菌O157∶H7 toxB基因缺失株的构建

为了明确肠出血性大肠杆菌(Enterohemorrhagic Escherichia coli)O157∶H7大质粒pO157编码的蛋白质ToxB与O157∶H7在肠道黏附、定殖的关系,构建含有toxB基因同源臂的重组自杀性质粒pMEG375-BN-Kan-BC,转化SM10宿主菌获得重组SM10(pMEG375-BN-Kan-BC)。将SM10(pMEG375-BN-Kan-BC)与O157∶H7进行混合培养,通过同源重组,获得杂交toxB基因缺失株。用体外接种的HEp-2细胞和体内感染链霉素处理的小鼠,明确缺失株黏附定殖能力。经PCR和Western blot鉴定,toxB基因被卡那霉素(Kan+)选择标记基因表达盒所代替。O157∶H7(△toxB)生长特性与亲本株相比无明显差异。O157∶H7(△toxB)与亲本株相比,对HEp-2细胞的黏附能力降低了2倍。口服感染小鼠后,O157∶H7(△toxB)第3 d粪便排菌量仅为3.1×105 CFU,持续排菌11 d;而亲本株排菌量高达4.03×107 CFU,持续排菌时间超过14 d。     

A bacterial protein targets the BAHD1 chromatin complex to stimulate type III interferon response

Intracellular pathogens such as Listeria monocytogenes subvert cellular functions through the interaction of bacterial effectors with host components. Here we found that a secreted listerial virulence factor, LntA, could target the chromatin repressor BAHD1 in the host cell nucleus to activate interferon (IFN)-stimulated genes (ISGs). IFN-λ expression was induced in response to infection of epithelial cells with bacteria lacking LntA; however, the BAHD1-chromatin associated complex repressed downstream ISGs. In contrast, in cells infected with lntA-expressing bacteria, LntA prevented BAHD1 recruitment to ISGs and stimulated their expression. Murine listeriosis decreased in BAHD1(+/-) mice or when lntA was constitutively expressed. Thus, the LntA-BAHD1 interplay may modulate IFN-λ-mediated immune response to control bacterial colonization of the host.     

嗜水管单胞菌超微结构的研究

嗜水气单胞菌的代表株Ｊ－Ｉ负染显示它具有一端生单鞭毛及周身菌毛,菌毛有两种形态：一种是短而硬（Ｂ菌毛）,数量多;另一种是细而长（Ｗ菌毛）,易弯曲,数量少。超薄切片可见在细胞外膜外有一层结构即Ｓ层,将提取的Ｓ层负染,可见晶格状规则排列的蛋白亚单位。不同的培养条件影响菌毛、Ｓ蛋白的表达。     

Complete genome sequence of Neisseria meningitidis serogroup B strain MC58

The 2,272,351-base pair genome of Neisseria meningitidis strain MC58 (serogroup B), a causative agent of meningitis and septicemia, contains 2158 predicted coding regions, 1158 (53.7%) of which were assigned a biological role. Three major islands of horizontal DNA transfer were identified; two of these contain genes encoding proteins involved in pathogenicity, and the third island contains coding sequences only for hypothetical proteins. Insights into the commensal and virulence behavior of N. meningitidis can be gleaned from the genome, in which sequences for structural proteins of the pilus are clustered and several coding regions unique to serogroup B capsular polysaccharide synthesis can be identified. Finally, N. meningitidis contains more genes that undergo phase variation than any pathogen studied to date, a mechanism that controls their expression and contributes to the evasion of the host immune system.     

Bleeding canker of pear——An emerging devastating disease

正Bleeding canker (BC) of pear trees,is a devastating disease in China.The disease was originally observed in Jiangsu Province and its causal agent was identified first as Erwinia sp.in the early 1970's and latter as a novel species,Dickeya fangzhongdai.BC is epidemically emerging prevalently from April to September annually in pear-growing regions in Zhejiang,Anhui and Shandong provinces,and threatening pear industry currently in China.To better control BC disease,it is crucial to know BC symptomatology,epidemics,etiology,and diagnostics first.The special topic of the three papers have well illustrated the points mentioned above.The first article by Chen et al.(2020b) described in detail the symptomatology,etiology and epidemiology of BC disease.BC mainly damages pear trunks and branches with no obvious symptoms early and bacterial rusty oozes mixed with tree saps exuded from died tissues later.The diseased portions display small soft and sap-filled brown spots or red streaks with strong smells likely of yeast fermentation.Importantly in this paper,the causal agent is identified as     

不同宿主植物对井陉矿区AM真菌繁殖的影响

温室盆栽条件下,以灭菌土[土∶沙=1∶1(V/V)]为基质,研究紫花苜蓿、黑麦草和高丹草对井陉煤矿菌根(AM)真菌生长繁殖的影响。结果表明,3种植物都能与AM真菌形成良好共生关系。综合分析孢子密度、总定殖率、菌丝定殖率、泡囊定殖率和SDH活性5项指标,发现紫花苜蓿作为宿主时AM真菌扩繁效果最好,孢子密度为5.03个/g,总定殖率为42.22%,菌丝定殖率为40.00%、泡囊定殖率为13.33%,SDH活性为31.11%。仅泡囊定殖率和SDH活性紫花苜蓿与高丹草差异不显著,与黑麦草差异显著;其他指标紫花苜蓿与黑麦草、高丹草均有显著差异。相关性分析表明,AM真菌孢子产量与定殖率、宿主植物生长状况无显著相关性。     

青枯雷尔氏菌致病机制及其相关基因的研究进展

阐述青枯雷尔氏菌致病基因以及它们之间的相互调节。由于青枯雷尔氏菌的复杂性,进而发展了许多青枯雷尔氏菌分子鉴定技术,并且对青枯雷尔氏菌的鉴定逐渐走向快速、便捷和灵敏高的趋势。青枯雷尔氏菌基因组约5.8Mb,具有高(G+C)含量和约5 120个可能的编码基因;它是由3.7Mb的染色体和2.1Mb的大质粒所组成,主要的致病因子有Ⅲ型hrp分泌系统产物、胞外多糖、细胞壁降解酶(包括果胶质酶以及纤维素酶等),其涉及的基因主要包括hrp基因簇、avr基因、毒性基因;青枯雷尔氏菌通过Ⅲ型分泌系统(T3SS)、II型分泌系统(T2SS)等分泌系统将多种毒性因子输送到胞外使寄主植物致病。同时,T3SS和T2SS之间也是相互影响的。上述致病因子的协调作用是由一个复杂的网络调节系统控制的,并以PhcA调节基因的启动和转录为核心,自动而精密地调节有关致病基因的表达及关闭,从而控制细菌的生长状态。