拉恩氏菌W25对缓冲容量的响应及其产酸特性

【目的】进一步了解拉恩氏菌W25的溶磷机理和对土壤缓冲容量的响应。【方法】在液体摇瓶培养过程中,采用调节培养液pH的方法研究模拟土壤的缓冲容量对拉恩氏菌W25溶磷量的影响;通过单因子试验和HPLC相结合的方法,研究不同碳源、磷源条件下W25的溶磷能力及产酸特性。【结果】拉恩氏菌W25在磷酸三钙培养液中培养120 h后有效磷含量达到最大值,培养液有效磷含量与培养液pH变化之间呈极显著负相关性(P<0.01);W25在培养第48?96 h具有较强的缓冲能力,培养液有效磷含量加碱处理与未加碱处理差异不显著(P<0.05),从第120 h开始,缓冲能力开始减弱,在168 h后基本丧失了缓冲能力;W25在不同碳源条件下溶磷能力差异显著(P<0.05),依次为葡萄糖>乳糖>蔗糖>甘露醇>淀粉,不同磷源中培养液有效磷含量差异极显著(P<0.01),依次为磷酸三钙>磷酸铁>磷酸铝>磷矿粉;不同碳源、磷源条件下W25培养液中有机酸的种类和浓度差异较大,W25溶磷能力的大小不仅与产酸的种类有关,而且也与产酸的浓度有关。【结论】研究结果为更深入研究拉恩氏菌溶磷机理提供条件,为拉恩氏菌的应用提供理论基础。     

多噬伯克霍尔德氏菌WS-FJ9对林木病原菌物的拮抗作用及代谢产物的稳定性

【背景】伯克霍尔德氏菌(Burkholderia)是一类重要的植物根际促生细菌,许多菌株具有抑制植物病原菌生长和促进植物生长等功能。【目的】探究高效解磷促生细菌多噬伯克霍尔德氏菌(B. multivorans) WS-FJ9对不同林木病原菌物的抑菌作用。【方法】采用平板对峙法检测菌株WS-FJ9对5株林木病原真菌和卵菌的抑制效果;基于比色法检测经菌株WS-FJ9处理后病原菌菌丝细胞内含物的变化;使用antiSMASH 5.0在线预测网站对其次生代谢物质进行预测;通过菌丝生长抑制速率法对其无菌发酵滤液的抑菌活性和稳定性进行研究。【结果】菌株WS-FJ9对5种林木病原菌均具有不同程度的抑制作用,其中菌悬液对樟疫霉(Phytophthora cinnamomi)的抑制作用最好,抑菌带宽度为14.82±0.20mm,无菌发酵滤液对真菌拟茎点霉(Phomopsismacrospore)和松杉球壳孢(Sphaeropsis sapinea)的抑制效果显著,抑菌率分别为62.22%和62.78%;经无菌发酵滤液处理后的病原菌菌丝内的丙二醛含量增高,还原糖和可溶性蛋白含量显著降低。WS-FJ9菌株的基因组中含27个不同的次级代谢产物编码基因簇,其中包含编码嗜铁素、细菌素和抗生素等抑菌基因簇;该菌株发酵液在高温、紫外照射和强酸强碱环境条件下及经蛋白酶处理后,其抑菌活性均未受到影响。【结论】多噬伯克霍尔德氏菌WS-FJ9对林木病原菌物具有很好的生防潜力。     

水霉拮抗菌的筛选及其拮抗作用的初步研究

为了获得水产动物水霉病病原菌的拮抗微生物,以水霉为靶标,对其拮抗菌进行了筛选,并研究了拮抗作用最强菌株的拮抗活性.实验结果表明:从发生过水霉病害的水体中分离得到了130株细菌,能抑制水霉菌落生长的有三株:LD038、LD057和LD106,其中以LD038的拮抗作用最强,经梅里埃ATB微生物自动鉴定系统鉴定为黏质沙雷氏菌(Serratia marcescens).培养基对LD038的拮抗活性影响显著,LD038在PDA平板上表现出的拮抗活性最强,大小依次为PDA＞BHI＞GY＞CA＞Sabouraud.进一步对菌株LD038体外拮抗活性进行了研究.平板抑制实验表明,LD038能抑制水霉菌丝生长和孢子萌发.琼脂扩散法中,LD038菌落周围产生的抑菌圈直径为20mm,而无菌水对照组中水霉菌丝蔓过滤纸纸片并长至平板边缘;D38菌线间孢子的萌发与孢子距菌线的距离有关,距LD038菌线22mm范围内,孢子的萌发完全被抑制.无菌发酵上清液实验表明,与对照组相比,LD038无菌发酵上清液对孢子的萌发和菌丝生长都表现出显著的抑制作用.其中孢子较菌丝对上清液更为敏感,5倍稀释上清液下的孢子萌发率仅为10%,且萌发后的菌丝生长也同样受到抑制,整个实验过程中菌丝均未形成网状,对照组中萌发形成的菌丝在16h后呈网状.无菌上清原液和2倍稀释上清液中孢子均未萌发.对菌丝而言,仅无菌上清原液能彻底抑制菌丝生长,与对照组相比,2倍和5倍稀释上清液显著延缓了菌丝的生长.当对照组中的菌丝铺满整孔时,2倍和5倍稀释上清液中的菌丝长度分别为0和2.6mm.显微观察表明LD038的无菌发酵上清液导致水霉菌丝形态发生变化,较正常菌丝短而粗大,且出现了黑色原生质聚集.本研究为水霉病害的生物防治提供了一定的理论基础和依据.     

一株产嗜铁素耐镉菌的分离及其对黑麦草种子萌发的作用

[背景]产嗜铁素细菌(Siderophore-Producing Bacteria,SPB)是一类耐重金属性能较好的促生微生物,将其应用于土壤重金属污染修复方面的研究已成为该领域的研究热点.[目标]为重金属镉污染土壤修复提供种质资源,并探究产嗜铁素细菌对Cd2+胁迫下黑麦草种子萌发的影响.[方法]采用微生物分离纯化技术...     

拮抗菌SB1的鉴定及其抗菌物质的分析

对番茄根系菌株SB1的抗菌活性进行测定,结果表明该菌株对多种植物病原真菌、细菌具有明显的抑制作用,表现出广谱抗菌活性。通过菌体形态、生理生化反应及16SrDNA序列分析,鉴定菌株SB1为枯草芽孢杆菌内生亚种。以青枯雷尔氏菌为指示菌,测定了菌株SB1抗菌物质的理化性质及组成。结果表明,其抗菌物质表现出良好的热稳定性、水溶性和醇溶性,且对紫外线照射和蛋白酶K处理不敏感。高效液相色谱分析结果进一步显示菌株SB1的抗菌物质中含有抗菌肽Surfactin。     

黄瓜枯萎病病原菌拮抗菌的筛选及其生物防治效应

分离筛选到一株对黄瓜枯萎病病原菌——尖孢镰刀菌具有显著拮抗作用的菌株YHJ15,并根据其生理生化特征和16SrRNA基因序列将其初步鉴定为短小芽孢杆菌;研究了其最适的生长条件。为黄瓜枯萎病的生物防治提供了种质资源。     

铜绿假单胞菌中S型绿脓杆菌素与荧光嗜铁素的功能协同性分析

在铜绿假单胞菌(Pseudomonas aeruginosa)中,S型绿脓杆菌素S2和S4与细菌中的铁载体荧光嗜铁素(pyoverdine)使用相同的摄取通道,表明二者之间存在某些联系。本研究表征了细菌中3个S型绿脓杆菌素(Pys2、PA3866、PyoS5)的单细菌基因表达分布,并研究了S2型绿脓杆菌素对细菌摄取荧光嗜铁素的影响。结果表明,在DNA损伤压力下,S型绿脓杆菌素基因的表达在细菌种群中呈现出高度分化,外源加入S2型绿脓杆菌素会减少细菌对荧光嗜铁素的摄取,因此S2型绿脓杆菌素的存在会阻止不合成荧光嗜铁素的“欺骗者”摄取环境中荧光嗜铁素,进而减弱其对活性氧(reactive oxygen species,ROS)压力的抵抗能力。另外我们发现,在细菌中过表达SOS响应(SOS response)调节因子PrtN时,荧光嗜铁素相关合成基因的表达量显著降低,进而导致荧光嗜铁素的总合成量和外分泌量显著降低。以上结果表明细菌中SOS压力响应系统与铁摄取系统的功能是存在相互联系的。     

嗜黏蛋白阿克曼氏菌治疗疾病的潜力与作用机制研究进展

嗜黏蛋白阿克曼氏菌(Akkermansia muciniphila, AKK)可促进肠道黏液分泌,维持肠道黏液动态平衡,调节肠黏膜屏障功能,在机体代谢调节、免疫应答中发挥重要作用。AKK对肠道炎症、神经炎症、机体代谢紊乱和癌症等疾病具有显著改善作用,被视为极具潜力的下一代益生菌。本文分别从消化系统、神经系统、代谢性紊乱和癌症等角度入手,系统概述AKK在疾病治疗中的潜力及作用分子机制。     

杉木炭疽病拮抗菌AM53的发酵条件优化

旨在优化地衣芽孢杆菌(Bacillus licheniformis)AM53的发酵条件。通过Plackett-Burman试验筛选到影响AM53活菌数的重要因素为培养温度、初始pH、摇床转速。经最陡爬坡试验和Box-Behnken试验,获得AM53的最佳发酵条件为培养温度30.5℃,初始pH8,摇床转速185 r/min,接种量为5%,培养24 h。结果显示,在此条件下,OD600平均为1.861,其值与预测值基本相符,说明该模型可信度高,可应用于AM53发酵条件优化。     

水霉拮抗菌的筛选与拮抗物特点初步分析

水霉病是淡水和咸淡水鱼类被水霉菌感染引起的常见疾病。该研究从多个养殖水体中分离得到6株水霉拮抗菌,SZK15、XL03、TG08、DJ12、HD05和DS08,以SZK15的拮抗作用最强。对SZK15研究发现,在PDA平板上,其对水霉菌丝抑制距离为11.5 mm,对水霉孢子抑制圈直径为29.7 mm,其10倍浓缩的无细胞发酵液的抑水霉菌圈直径达30.2 mm;在液体培养条件下,SZK15无细胞发酵原液能完全抑制水霉菌丝和孢子的萌发生长,其5倍稀释液中,水霉菌丝生长受抑制而长度稳定在2.0 mm,有30%的孢子萌发,且萌发后菌丝受抑制而未形成菌丝网,其10倍稀释液中水霉菌丝生长慢于对照组。SZK15分泌的拮抗活性物质对121℃高温敏感,对80℃、100℃高温、蛋白酶K和胰蛋白酶均部分敏感。本研究为水霉病害的生物防治提供了潜在新途径。     

Biological control of bacterial spot of tomato caused by Xanthomonas campestris pv. vesicatoria by Rahnella aquatilis

Xanthomonas campestris pv. vesicatoria strain 2 was isolated from infected tomato seedlings grown in open field in Egypt. This strain produced irregular yellow-necrotic areas on tomato leaves and spotting of the stem. In an attempt to control this disease biologically, four experiments were conducted and tomato seedlings were pretreated, before the pathogen, with either of two antagonistic strains of Rahnella aquatilis through leaves, roots, soil or seeds. In all experiments, seedlings pretreated with R. aquatilis showed reduced susceptibility toward X. c. pv. vesicatoria. They also contained reduced protein concentration and showed reduced number of protein bands in SDS-PAGE analysis as well as increased fresh and dry weight relative to control seedlings inoculated with the pathogen only. This indicates that R. aquatilis reduced the deleterious effect and the stress exerted by X. c. pv. vesicatoria on tomato seedlings. Foliar application of R. aquatilis was the most effective method in disease reduction which could be attributed to the direct effect of the antagonistic bacteria on the pathogen. The highest amounts of fresh and dry weight ere obtained from seed treatment, which might suggest that bacterial seed inoculation provides earlier protection than could be achieved with foliar, soil or root treatment.     

Purification and partial characterization of an outer membrane protein involved in the adhesion of Rahnella aquatilis to wheat roots

Abstract A 38 kDa major outer membrane protein isolated from the nitrogen-fixing enterobacterium Rahnella aquatilis CF3 showed high affinity for wheat roots in an in vitro adhesion assay. Antibodies directed against the 38 kDa protein were able to bind to whole cells of R. aquatilis and strongly reduced attachment to wheat roots, suggesting a role in adhesion to and colonization of plant roots. The N-terminal sequence of the 38 kDa protein revealed a strong homology with enterobacterial porins.     

Freezing and freeze-drying of the bacterium Rahnella aquatilis BNM 0523: study of protecting agents, rehydration media and freezing temperatures

Aims: The aim of the present study was to evaluate and compare freezing and freeze‐drying treatments for conserving Rahnella aquatilis (BNM 0523) with the goal to achieve an adequate commercial formulation of this biocontrol agent. Methods and Results: The effect of several protective agents, rehydration media and freezing temperatures on the viability and functional activity of the R. aquatilis was investigated. The storage stability at 3 months and 4 years was determined by checking the viability of the cells and their biocontrol capability against Botrytis cinerea by measuring the percentage of reduction of disease severity on apple. The best results were obtained by the freeze‐drying of the cells using a mixture of skimmed nonfat milk 10%, yeast extract 0·5% and glucose 1% as the protecting and rehydrating medium, and a quickly freezing (?70°C) before the freeze‐drying. In this case, the viability of the cells after 4 years was 98%, and their antagonistic ability showed a little decrease with respect fresh cells. Conclusions: The studies showed that R. aquatilis was resistant to freezing and freeze‐drying when it was used a mixture of cryoprotectants and that it was possible to obtain inoculums with high viability and good effectiveness for reduction of decay caused by B. cinerea. Significance and Impact of the study: This study is probably the first report about the resistance of R. aquatilis to freezing and freeze‐drying treatments and shows that these operations could be useful for obtaining a commercial formulation of this biocontrol agent.     

Effects of Rahnella aquatilis JZ-GX1 on Treat Chlorosis Induced by Iron Deficiency in Cinnamomum camphora

Journal of Plant Growth Regulation - With the increasing popularity of urban landscaping, there is a greater need to address iron deficiency and chlorosis in Cinnamomum camphora. Beneficial...     

Structure of the O-polysaccharide of the lipopolysaccharide of Rahnella aquatilis 1-95

The O-polysaccharide was isolated by mild acid hydrolysis of the lipopolysaccharide of Rahnella aquatilis 1-95 and studied by sugar and methylation analyses along with 1H and 13C NMR spectroscopy, including NOESY and 1H,13C HSQC experiments for linkage and sequence analysis. The following structure of the branched trisaccharide repeating unit of the O-polysaccharide was established: [carbohydrate structure: see text].     

Chemical characteristics and endotoxic activity of the lipopolysaccharide of Rahnella aquatilis 2-95

The lipopolysaccharide (LPS) from a new Enterobacteriaceae species, Rahnella aquatilis 2-95, was isolated and investigated. The structural components of the LPS molecule, namely, lipid A, core oligosaccharide, and O-specific polysaccharide, were obtained by mild acid hydrolysis. In lipid A, 3-oxytetradecanoic and tetradecanoic acids were found to be the predominant fatty acids. The major monosaccharides of the core oligosaccharide were galactose, arabinose, fucose, rhamnose, and an unidentified component. The O-specific polysaccharide was found to be assembled of a repeated trisaccharide unit of the following structure: The R. aquatilis 2-95 LPS is less toxic and more pyrogenic than the LPS from the R. aquatilis 1-95 strain studied earlier. Both acyl and phosphate groups are essential for toxic and pyrogenic activity of R. aquatilis 2-95 LPS.     

Biological control of common blight of bean (Phaseolus vulgaris) causedby Xanthomonas axonopodis pv. phaseoli by using the bacteriumRahnella aquatilis

The aim of this study was to evaluate the bacterium Rahnella aquatilis (Ra) for protection of bean plants against common blight disease caused by Xanthomonas axonopodis pv. phaseoli (Xap). Xap isolates were isolated from a naturally blighted leaves of bean plants grown in Assiut governorate. The blight symptoms were produced by all three isolates, but the isolates differed in their degree of the pathogenicity. Xap1 was the most virulence one against bean plants. The effect of Ra against common blight of bean plant was tested. In vitro studies, Ra exhibited inhibitor effect against the pathogen. Under greenhouse and field conditions, beanvariety “Giza 6” treated by Ra resulted in marked disease suppression. Ahigh decrease of the disease was correlated with a reduction of the bacterial multiplication. In physiological studies, bean plants treated by Ra exhibited higher phenolic compounds contents and higher activity of peroxidase (PO) enzyme than untreated plants. In conclusion, application of Ra was effective and could be recommended for controlling the bean common blight disease.     

Isolation and identification of Bacillus subtilis strain YB-05 and its antifungal substances showing antagonism against Gaeumannomyces graminis var. tritici

In this study, 98 putative Bacillus strains were isolated from wheat rhizospheric soil. Among the isolated strains, six showed strong inhibitory effects against the wheat take-all pathogen, Gaeumannomyces graminis var. tritici. One of the strains that showed significant inhibitory activity, YB-05, was identified as Bacillus subtilis based on a phylogenetic analysis of its 16S rDNA gene sequence, the results of the PCR analysis and cloning of its antifungal genes, its morphological characteristics and its physiological and biochemical properties. When tested with a dual-culture, cup–disc method and laboratory greenhouse studies, strain YB-05 was found to be superior to chemical treatment for control of the plant pathogen G. graminis var. tritici. After liquid culture, various antimicrobial substances in the culture medium were detected by high-performance liquid chromatography and high-resolution mass spectrometry, and the existence of their corresponding genes was verified by PCR analysis.