兰科植物内生细菌物种多样性及其促生机理研究进展

内生细菌影响兰科植物菌根形成和共生关系的稳定性,在兰科植物的生活史中起着重要作用。内生细菌通过分泌植物激素、采用光合作用、生物固氮或促进矿质营养的循环以及产生铁载体、合成其他活性物质等途径来促进兰科植物生长发育。综述了兰科植物内生细菌物种多样性的研究方法及其对兰科植物的促生机理,基于兰科植物与共生微生物的密切关系,认为内生细菌间、内生细菌与兰科植物菌根真菌间的互作是揭示兰科植物与内生细菌互作机理的重要方向。     

土壤产铁载体细菌的筛选及其对铁氧化物的活化与利用

【背景】土壤中铁主要以难溶态铁氧化物的形式存在,有效性较低,产铁载体细菌对铁氧化物的活化是提高铁利用效率的有效途径。【目的】从林木土壤筛选产铁载体细菌,并观察菌株对难溶性铁氧化物的利用效应,可为土壤微生物资源开发及其在养分调控中的作用提供理论依据。【方法】通过CAS检测法从林木根系附近表层土壤中分离产铁载体细菌,借助生物培养实验分析温度和pH对微生物生长和铁载体产生的影响,通过振荡平衡实验,探究细菌产铁载体对铁氧化物的活化效应。【结果】通过CAS检测法从林木根系附近表层土壤中分离得到12株产铁载体细菌,16S rRNA基因扩增子测序初步鉴定结果显示筛选细菌均为假单胞菌属。选取铁载体产生能力和生长活性较高的两株细菌ARSB02和CNRSB01作为重点研究对象,结果显示,不同条件下CNRSB01的生物量和铁载体产量均高于菌株ARSB02,22 h时菌株ARSB02和CNRSB01的铁载体活性单位分别达到67.07%和84.60%。pH 5.0-8.0的范围内两株细菌可以保持较好的铁载体产生能力,菌株ARSB02和CNRSB01在pH7.0时铁载体产生能力最强,铁载体活性单位分别达到38.9...     

中药渣堆肥中解磷细菌的筛选、鉴定及其拮抗作用

为开发新型、安全及高效的微生物菌肥,以堆肥2个月后的中药渣为试材,筛选解磷拮抗细菌。用有机磷细菌培养基初步筛选5株解磷细菌;采用溶磷圈法和磷钼蓝比色法测定初筛菌株的解磷作用,解磷作用最优的菌株是YP5;通过形态学特征观察、生理生化试验和16S rDNA序列分析鉴定,确定菌株YP5为铜绿假单胞菌(Pseudomonas aeruginosa)。促生拮抗因子测定结果表明菌株YP5能分泌铁载体和大量胞外蛋白酶;药敏实验结果显示菌株YP5对诺氟沙星、氯霉素、庆大霉素、恩诺沙星、丁胺卡那霉素高度敏感;分别采用平板对峙法和带毒培养基法测定结果表明菌株 YP5发酵液和无菌滤液均对冬瓜根腐病等9种植物病原菌有良好的拮抗作用,抑菌率最高达80%以上。高效液相色谱测定菌株YP5在28℃、KB培养基中抗菌代谢物申嗪霉素的产量最高,为17.73 mg/L。     

病原菌的自我防御

在制药和植物保护领域,20世纪已经广泛研究了自然界中常见微生物抑制生长的现象和有毒微生物的代谢活动。在过去10 a里,将拮抗物引入植物表面、生长介质以及繁殖材料中的生物防治方法引起的兴趣还在不断增加。但是病原物针对生防因子、化学药物等所进行的自我防御工作则研究的比较少。主要讨论当前病原菌抵抗微生物拮抗机制的观点和概念,以及所关注的植物病原真菌和细菌的防御。     

微生物产铁载体研究

铁元素在微生物生长过程中占有重要地位。自然界中铁元素含量十分丰富,但很多存在形式不能被微生物直接利用。在物竞天择的大环境中,微生物产生铁载体来满足自身生长需要。本文就铁载体的作用,分类,产生机制及其检测方法作以综述。     

黑麦草根际产铁载体细菌HMGY6B的筛选鉴定及对病原菌的拮抗作用

【目的】从石灰性土壤中分离筛选出铁载体合成能力强、抗病效果好的菌株。【方法】采用刃天青(Chrome azural S,CAS)平板检测法,定性、定量筛选产铁载体能力较强的菌株,通过菌株形态、生理生化特征、16S r RNA基因序列相似性和系统发育分析,鉴定细菌类型,然后采用平板对峙法研究菌株与病原菌的拮抗作用。【结果】从多年生黑麦草根际土壤中分离得到一株产铁载体能力很强的菌株HMGY6B,经鉴定,该菌属假单胞菌属Pseudomonas菌株,其产生的儿茶酚型铁载体对黄瓜灰霉病(Botrytis cinerea)有显著的拮抗作用,在低铁条件下(0.16、2、5、10μmol/L FeCl_3)对黄瓜灰霉病的生长抑制率高达91.2%,但在富铁条件下(50μmol/L FeCl_3)降为30.2%,100μmol/L FeCl_3抑制率仅为5.5%。【结论】菌株HMGY6B可用于今后复合型抗病生物菌肥的开发研制。     

病原菌负反馈作用促进物种共存的研究进展

植物病原菌包括真菌、细菌、病毒等,广泛存在于自然界中,可以引起各种植物病害。病原菌对植物的负反馈作用,即植物个体附近的土壤病原菌,可能反过来侵害其自身或同种个体,致死或影响生长植物的现象。植物病原菌对群落中优势种的更新有强烈的抑制作用,从而促进物种的共存。植物病原菌的负反馈作用在植物种群动态和群落演替中起着重要的调控作用。     

高产铁载体假单胞菌的筛选及其对铁氧化物的利用

筛选高产铁载体的微生物,研究铁载体的抑菌作用和对不溶性未定型铁氧化物(poorly crystalline iron hydroxides,PCIH)的利用。CAS法筛选高产铁载体菌株,采用琼脂扩散法和生长抑制测定铁载体的抑菌作用,利用16S r RNA基因序列比对鉴定分离菌株,并根据分离菌株的生长情况,确定铁载体对不溶性PCIH的利用。从土壤样品中共筛选到172株产铁载体的菌株,高产铁载体菌株13株,其中仅有菌株Z158的发酵液对金黄色葡萄球菌、藤黄微球菌、普通变形杆菌和副溶血性弧菌具有抑菌作用,抑菌率分别为51.3%、50.2%、37.1%和28.0%。比对该菌株的16S r RNA基因序列,确定Z158属于Pseudomonas aeruginosa。当不溶性的PCIH作为唯一可利用的铁源时,菌株Z158培养24 h的生物量比无铁条件下提高了46.1%。铜绿假单胞菌Z158分泌的铁载体能够抑制病原菌的生长,同时还能获取不溶性未定型铁氧化物PCIH中的铁元素。     

外生菌根真菌对植物根病原菌拮抗作用的研究

■的15株外生菌根真菌在琼脂平板上对6株植物病原菌的拮抗作用试验结果表明,美味红菇、劣味乳菇、毛边滑锈伞、大毒滑锈伞等菌根菌对试验病原菌的营养菌丝具有明显的拮抗作用。菌根菌的培养液中含有抑制根病原菌的活性物质,且对高温稳定。外生菌根菌在纯培养条件下对病原菌的拮抗作用包括菌丝体对峙生长作用,重寄生作用和拮抗活性物质作用。其中菌丝体的重寄生作用在抗病效应中起重要作用。     

冬小麦植物铁载体分泌的杂种效应

缺铁是石灰性土壤常见的植物营养问题之一.禾本科植物种或基因型的植物铁载体分泌能力与耐缺铁有关,提高植物铁载体分泌能力是改良缺铁的土壤上植物铁aestivum L.) 3个杂交种及其4个亲本在缺铁营养液中植物铁载体的分泌及杂种的效应.植物铁载体的分泌率通过根分泌物对新形成的Fe(OH)3的活化能力进行测定, 在缺铁症出现时每隔2、3天测定1次.在缺铁条件下,所有基因型都分泌较多的植物铁载体,并且随缺铁症状的发展分泌量增加.杂交种具有对缺铁更敏感的反馈系统,在缺铁条件下,杂交种比亲本分泌铁载体的速度更快、量更高.通过分析杂交种和亲本的关系,认为可以通过对亲本分泌植物铁载体能力和配合力的选择,利用杂种优势来提高小麦铁的利用效率.     

Development of a detection system for ferric pseudobactin using monoclonal antibodies

Certain root-colonizing fluorescent pseudomonads have been shown to promote plant growth and prevent plant disease in part through the production of siderophores. However, these favorable results have not been reproduced consistently from the laboratory to the greenhouse or from the greenhouse to the field. In some circumstances siderophores appear to play no role in disease prevention. In order to understand the dynamics of competition for iron in the rhizosphere it is essential that the localization and concentration of siderophores produced by both biocontrol agents and plant pathogens be determined. We have produced monoclonal antibodies (MAbs) to ferric pseudobactin, the siderophore of plant growth-promoting Pseudomonas B10. Three IgG1 MAbs cross-react with certain ferric pseudobactins but not with others. A competitive ELISA has been developed to detect and quantify ferric pseudobactin.     

Marine Siderophores and Microbial Iron Mobilization

Iron is essential for the growth of nearly all microorganisms yet iron is only sparingly soluble near the neutral pH, aerobic conditions in which many microorganisms grow. The pH of ocean water is even higher, thereby further lowering the concentration of dissolved ferric ion. To compound the problem of availability, the total iron concentration is surprisingly low in surface ocean water, yet nevertheless, marine microorganisms still require iron for growth. Like terrestrial bacterial, bacteria isolated from open ocean water often produce siderophores, which are low molecular weight chelating ligands that facilitate the microbial acquisition of iron. The present review summarizes the structures of siderophores produced by marine bacteria and the emerging characteristics that distinguish marine siderophores.     

A new fluorimetric method for the detection and quantification of siderophores using Calcein Blue,with potential as a bacterial detection tool

The presence of microorganisms in biological fluids like urine and blood is an indication of vulnerability to infections. Iron is one of the important micronutrients required for bacterial growth. In an iron-deficit environment, bacteria release high-affinity iron-chelating compounds called siderophores which can be used as non-invasive target molecules for the detection of such pathogens. However, only limited reagents and procedures are available to detect the presence of these organic molecules. The present study aims at detecting the presence of siderophores in the iron-depleted media, exploiting the reversible quenching of Calcein Blue and iron(III) complex. The fluorescence of Calcein Blue is known to be quenched in the presence of iron(III); if a stronger chelator removes this ion from the fluorophore, the fluorescence of the fluorophore is regained. This behaviour of the fluorophore was exploited to detect and quantify siderophores down to 50 and 800 nM equivalent of standard siderophore, deferroxamine mesylate (desferal) in Dulbecco’s PBS and siderophore quantification (SPQ) medium, respectively. The siderophores released by pathogens, equivalent to standard desferal, were in the range of 1.29 to 5.00 μM and those for non-pathogens were below 1.19 μM. The simple, sensitive and cost-effective method performed in a 96-well plate was able to detect and quantify iron chelators within 7–8 h of incubation.     

Iron transport-mediated antagonism between plant growth-promoting and plant-deleterious Pseudomonas strains

Both plant growth-promoting Pseudomonas B10 and its yellow-green, fluorescent iron transport agent (siderophore) pseudobactin enhance potato growth and biologically control certain soil-borne fungal diseases in part by depriving specific root-colonizing endemic microorganisms including phytopathogens of iron(III), thus inhibiting their growth. The present study examines this mode of iron deprivation. The growth inhibition of certain bean-deleterious fluorescent pseudomonads by specific bean-beneficial fluorescent pseudomonads is due in part to the inability of susceptible strains to utilize siderophores from beneficial strains to transport iron(III). Conversely, deleterious strains which were able to utilize siderophores from beneficial strains were not inhibited. The ability of a given pseudomonad to utilize another pseudomonad's siderophore may depend upon its possessing a specific outer membrane receptor protein for that pseudomonad's ferric siderophore. Siderophore-mediated competition for iron in microbial systems appears to be a widespread phenomenon.     

Iron uptake and metabolism in the rhizobia/legume symbioses

Iron-containing proteins figure prominently in the nitrogen-fixing symbioses between bacteria of the genera Azorhizovium, Bradyrhizobium and Rhizobium and their respective plant hosts. Although iron is abundant in the soil, the acquisition of iron is problematic due to its low solubility at biological pH under aerobic conditions. The study of iron acquisition as it pertains to these economically important symbioses is directed at answering three questions: 1) how do rhizobial cells acquire iron as free-living microorganisms where they must compete for this nutrient with other soil inhabitants 2) how do the plant hosts acquire enough iron for the symbiosis and 3) how do rhizobia acquire iron as symbionts? Production and/or utilization of ferric-specific ligands (siderophores) has now been documented in the laboratory for a number of rhizobial species, but there is limited information on whether production and/or untilization occurs either in the soil or in planta. Studies with rhizobial mutants which can no longer produce and/or utilize siderophores should address whether siderophores contribute to functional symbioses. In addition, the ability to produce and/or utilize siderophores may affect the outcome of both interstrain and interspecific competition in the rhizosphere and in bulk soil. Some progress has been made at documenting the effects of iron deficiency on nodule development. Studies are also underway to determine whether, in addition to its central structural role, iron may also play a regulatory role in the symbioses. This review is an attempt to give an overview of the field, and hopefully will stimulate further research on the iron nutrition of these symbioses which account for such a significant proportion of the world's biologically fixed nitrogen.     

Bacterial siderophores efficiently provide iron to iron-starved tomato plants in hydroponics culture

Iron is one of the essential elements for a proper plant development. Providing plants with an accessible form of iron is crucial when it is scant or unavailable in soils. Chemical chelates are the only current alternative and are highly stable in soils, therefore, posing a threat to drinking water. The aim of this investigation was to quantify siderophores produced by two bacterial strains and to determine if these bacterial siderophores would palliate chlorotic symptoms of iron-starved tomato plants. For this purpose, siderophore production in MM9 medium by two selected bacterial strains was quantified, and the best was used for biological assay. Bacterial culture media free of bacteria (S) and with bacterial cells (BS), both supplemented with Fe were delivered to 12-week-old plants grown under iron starvation in hydroponic conditions; controls with full Hoagland solution, iron-free Hoagland solution and water were also conducted. Treatments were applied twice along the experiment, with a week in between. At harvest, plant yield, chlorophyll content and nutritional status in leaves were measured. Both the bacterial siderophore treatments significantly increased plant yield, chlorophyll and iron content over the positive controls with full Hoagland solution, indicating that siderophores are effective in providing Fe to the plant, either with or without the presence of bacteria. In summary, siderophores from strain Chryseobacterium C138 are effective in supplying Fe to iron-starved tomato plants by the roots, either with or without the presence of bacteria. Based on the amount of siderophores produced, an effective and economically feasible organic Fe chelator could be developed.     

Fate of ferrisiderophores after import across bacterial outer membranes: different iron release strategies are observed in the cytoplasm or periplasm depending on the siderophore pathways

Siderophore production and utilization is one of the major strategies deployed by bacteria to get access to iron, a key nutrient for bacterial growth. The biological function of siderophores is to solubilize iron in the bacterial environment and to shuttle it back to the cytoplasm of the microorganisms. This uptake process for Gram-negative species involves TonB-dependent transporters for translocation across the outer membranes. In Escherichia coli and many other Gram-negative bacteria, ABC transporters associated with periplasmic binding proteins import ferrisiderophores across cytoplasmic membranes. Recent data reveal that in some siderophore pathways, this step can also be carried out by proton-motive force-dependent permeases, for example the ferrichrome and ferripyochelin pathways in Pseudomonas aeruginosa. Iron is then released from the siderophores in the bacterial cytoplasm by different enzymatic mechanisms depending on the nature of the siderophore. Another strategy has been reported for the pyoverdine pathway in P. aeruginosa: iron is released from the siderophore in the periplasm and only siderophore-free iron is transported into the cytoplasm by an ABC transporter having two atypical periplasmic binding proteins. This review presents recent findings concerning both ferrisiderophore and siderophore-free iron transport across bacterial cytoplasmic membranes and considers current knowledge about the mechanisms involved in iron release from siderophores.     

Iron uptake mechanisms as key virulence factors in bacterial fish pathogens

This review summarizes the current knowledge about iron uptake systems in bacterial fish pathogens and their involvement in the infective process. Like most animal pathogens, fish pathogens have evolved sophisticated iron uptake mechanisms some of which are key virulence factors for colonization of the host. Among these systems, siderophore production and heme uptake systems are the best studied in fish pathogenic bacteria. Siderophores like anguibactin or piscibactin, have been described in Vibrio and Photobacterium pathogens as key virulence factors to cause disease in fish. In many other bacterial fish pathogens production of siderophores was demonstrated but the compounds were not yet chemically characterized and their role in virulence was not determined. The role of heme uptake in virulence was not yet clearly elucidated in fish pathogens although there exist evidence that these systems are expressed in fish tissues during infection. The relationship of other systems, like Fe(II) transporters or the use of citrate as iron carrier, with virulence is also unclear. Future trends of research on all these iron uptake mechanisms in bacterial fish pathogens are also discussed.     

Small-molecule inhibition of siderophore biosynthesis in Mycobacterium tuberculosis and Yersinia pestis

Mycobacterium tuberculosis and Yersinia pestis, the causative agents of tuberculosis and plague, respectively, are pathogens with serious ongoing impact on global public health and potential use as agents of bioterrorism. Both pathogens have iron acquisition systems based on siderophores, secreted iron-chelating compounds with extremely high Fe3+ affinity. Several lines of evidence suggest that siderophores have a critical role in bacterial iron acquisition inside the human host, where the free iron concentration is well below that required for bacterial growth and virulence. Thus, siderophore biosynthesis is an attractive target in the development of new antibiotics to treat tuberculosis and plague. In particular, such drugs, alone or as part of combination therapies, could provide a valuable new line of defense against intractable multiple-drug-resistant infections. Here, we report the design, synthesis and biological evaluation of a mechanism-based inhibitor of domain salicylation enzymes required for siderophore biosynthesis in M. tuberculosis and Y. pestis. This new antibiotic inhibits siderophore biosynthesis and growth of M. tuberculosis and Y. pestis under iron-limiting conditions.     

Siderophores in environmental research: roles and applications

Siderophores are organic compounds with low molecular masses that are produced by microorganisms and plants growing under low iron conditions. The primary function of these compounds is to chelate the ferric iron [Fe(III)] from different terrestrial and aquatic habitats and thereby make it available for microbial and plant cells. Siderophores have received much attention in recent years because of their potential roles and applications in various areas of environmental research. Their significance in these applications is because siderophores have the ability to bind a variety of metals in addition to iron, and they have a wide range of chemical structures and specific properties. For instance, siderophores function as biocontrols, biosensors, and bioremediation and chelation agents, in addition to their important role in weathering soil minerals and enhancing plant growth. The aim of this literature review is to outline and discuss the important roles and functions of siderophores in different environmental habitats and emphasize the significant roles that these small organic molecules could play in applied environmental processes.