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微生物肥料的作用机理、现状及展望

花匠小妙招
2024-11-17 00:59

0 引言

农业生产一直依赖化学合成品来优化作物，包括利用化学肥料增加作物产量、化学农药减轻病原菌对作物的损害[1]。但是过度使用化学肥料不仅污染空气和水质[2]，还会导致土壤退化、酸化以及土壤有机质流失等[3]。而过度使用化学农药导致病原菌耐药性增强，药效降低。为了解决诸如作物产量和质量下降、病原菌耐药性增强和环境污染等问题，急需探索开发更多非化学防治措施。替代化学肥料的方法之一是利用微生物肥料，即向土壤中添加有益微生物及其代谢产物。这是以微生物的生命活动为核心，使农作物获得特定肥效的一类肥料制品。应用微生物肥料促进作物的生长和产量提高，增强作物的系统抗性，维持农田生态系统的稳定，是解决当前农业问题的可行性策略[4]。目前微生物肥料普遍存在产品同质性高，使用中稳定性差、普适性低等问题[5]。主要原因在于对微生物、微生物代谢物、植物和土壤环境之间相互作用关系知识的缺乏，以及高效可用菌种较少，企业生产技术落后等。施用生物肥料替代部分化肥是目前最新的农业趋势，这也是实现农业可持续发展的较好选择，对缓解自然环境污染的恶化，减少化肥需求具有重要意义。微生物肥料产品的成功与否取决于其中的植物促生菌(Plant Growth Promoting Bacteria, PGPB)在土壤中的生存能力、与接种作物的相容性、与土著微生物群的相互作用能力等等[6]，这就需要我们对植物促生菌有更深入的理解和认识。本综述系统介绍了微生物肥料的分类与应用，并从微生物次生代谢物的角度出发，解释有益微生物菌剂如何通过次生代谢物促进植物生长和提高植物对非生物和生物胁迫的耐受性，强调其作为微生物肥料的核心原料替代化学肥料的潜力与挑战。

1 微生物肥料的研究现状

1.1 概念

微生物肥料是含有益微生物活细胞的微生物制剂，施用于植物种子、根际或土壤时，通过生物活性调动营养物质，将土壤矿物质和植物凋落物转化为有效形态，并帮助建立缺失的微生物菌群，从而改善土壤状况。近年来，微生物肥料成为生物固氮、溶磷、解钾的重要组成部分，它们为植物提供了经济上有吸引力和生态上合理的营养途径，是化学肥料理想的补充或替代品。

1.2 分类与应用

早在19世纪末，欧洲国家就开始利用根瘤菌和硝化细菌为主要菌群制备微生物肥料，开启了微生物肥料市场应用的时代。中国微生物肥料产业的发展和应用始于20世纪40年代，主要以根瘤菌应用为主。随着农业的发展，对新型多样化的肥料需求增加，微生物肥料产业在80年代后期迅速发展，生产也逐渐由小作坊发展到规模化、产业化的正规企业。之后中国制定了一系列微生物肥料的标准体系，并推行微生物肥料登记政策，进一步规范了微生物肥料市场[7]。基于目前对微生物肥料的研究和行业分类，微生物肥料分为菌剂类产品和菌肥类产品。菌剂类产品包含根瘤菌剂、固氮菌剂、溶磷菌剂、光合菌剂和土壤修复菌剂等9种类型；菌肥类产品可分为复合微生物肥和生物有机肥2种类型（

表1

）。

表1 微生物肥料产品分类 产品类型制备规则菌种菌剂类根瘤菌剂以根瘤菌为生产菌种制成的微生物接种剂花生根瘤菌、大豆根瘤菌、紫云英根瘤菌、埃氏慢生根瘤菌、豌豆根瘤菌等固氮菌剂以自生固氮菌和/或联合固氮菌为生产菌种制成的微生物接种剂慢生根瘤菌、偶氮根瘤菌、雀稗固氮菌、巴西固氮螺菌、圆褐固氮菌、瓦恩兰德固氮菌、阴沟肠杆菌等溶磷菌剂以溶磷微生物为生产菌种制成的微生物接种剂多粘类芽孢杆菌、枯草芽孢杆菌、地衣芽孢杆菌、洋葱伯克霍尔德氏菌、草生欧文氏菌变种、青霉属、柠檬酸杆菌、沙福芽孢杆菌等光合菌剂以光合细菌为生产菌种制成的微生物接种剂沼泽红假单胞菌、嗜酸红假单胞菌、类球红细菌、血红红假单胞菌、类球红细菌等硅酸盐细菌以硅酸盐细菌为生产菌种制成的微生物接种剂胶质芽孢杆菌、土壤芽孢杆菌、嗜酸氧化硫杆菌、邻单胞菌、阪崎肠杆菌、枯草芽孢杆菌等菌根菌剂以菌根真菌为生产菌种制成的微生物接种剂球孢囊霉门真菌、伊朗球囊霉、根内根孢囊霉等促生菌剂以植物促生根圈微生物为生产菌种制成的微生物接种剂解淀粉芽孢杆菌、短小芽胞杆菌、蕈状芽孢杆菌、荧光假单孢菌、多粘芽孢杆菌、地衣芽孢杆菌、变形杆菌、伯克霍尔德菌、鞘氨醇单胞菌、木霉菌等有机物料腐熟菌剂能加速各种有机物料（包括作物秸秆、畜禽粪便、生活垃圾及城市污泥等）分解、腐熟的微生物接种剂多粘类芽孢杆菌、枯草芽孢杆菌、地衣芽孢杆菌、戊糖片球菌、米根霉、粉状毕赤酵母、米曲霉、酿酒酵母、黑曲霉、白地霉、嗜热脂肪地芽孢杆菌、植物乳杆菌、嗜热性侧孢霉、绿色木霉、温特曲霉、帚状曲霉、热紫链霉菌生物修复菌剂能通过微生物的生长代谢活动，使环境中的有害物质浓度减少、毒性降低或无害化的微生物接种剂枯草芽孢杆菌、胶冻样类芽孢杆菌、巨大芽孢杆菌、嗜酸乳杆菌、德氏乳杆菌、多粘类芽孢杆菌、地衣芽孢杆菌、米曲霉、黑曲霉、绿色木霉、侧孢短芽孢杆菌、弗氏链霉菌、贝莱斯芽孢杆菌、阿氏芽孢杆菌、阿维菌素链霉菌、长枝木霉、淡紫拟青霉菌肥类复合微生物肥料目的微生物经工业化生产增殖后与营养物质复合而成的活菌制品枯草芽孢杆菌、胶冻样类芽孢杆菌、侧孢短芽孢杆菌、沼泽红假单胞菌、巨大芽孢杆菌、嗜酸乳杆菌、细黄链霉菌、固氮类芽孢杆菌、多粘类芽孢杆菌、短短芽孢杆菌、地衣芽孢杆菌、粉状毕赤酵母、米曲霉、酿酒酵母、长枝木霉、蕈状芽孢杆菌、娄彻氏链霉菌、乳酸可鲁维酵母等生物有机肥目的微生物经工业化生产增殖后与主要以动植物残体（如畜禽粪便、农作物秸秆等）为来源并经无害化处理的有机物料复合而成的活菌制品。枯草芽孢杆菌、胶冻样类芽孢杆菌、侧孢短芽孢杆菌、巨大芽孢杆菌、酿酒酵母、嗜酸乳杆菌、细黄链霉菌、多粘类芽孢杆菌、地衣芽孢杆菌、粉状毕赤酵母、米曲霉、酿酒酵母、光孢青霉、植物乳杆菌、嗜热性侧孢霉、干酪乳杆菌、绿色木霉、金龟子绿僵菌、甲基营养型芽孢杆菌、长枝木霉等注：根据农业农村部微生物肥料和食用菌菌种质量监督检验测试中心《登记产品》整理。

为了更好地研究和利用微生物资源，中国先后建立了多个各具特色的微生物资源保藏中心，包括中国农业微生物菌种保藏中心、中国普通微生物菌种保藏中心、农业微生物种质及遗传资源保藏和利用中心、广东微生物菌种保藏中心，以及针对根瘤菌研究的中国农业大学根瘤菌研究中心，针对芽孢杆菌研究的福建芽孢杆菌资源保存中心等等[8]。微生物肥料所用菌种也从根瘤菌逐步发展到细菌、链霉菌、酵母、真菌等多种类型（

表1

）。同时，为了满足各类植物生长的需求，微生物肥料适用植物也不局限于水稻、小麦、玉米、花生、白菜、番茄等重要粮食和蔬菜作物，近年来也推出了适用于百香果、火龙果、藜麦、当归、黄芪等经济作物的微生物肥料[9]。

与传统肥料相比，微生物肥料具有提高肥料利用率和农作物品质、保护生态环境和土壤健康等多种优点。有研究证实，施加根瘤菌剂能在寄主植物的根或茎上诱导形成独特的根瘤，在这些根瘤中，根瘤菌将大气中的氮气转化为植物所需的氨。同时，根瘤菌还能强烈抑制豆根腐烂，提高作物产量[10]。进一步研究证实，在减少化学氮肥施用量、添加根瘤菌剂的条件下，大豆平均产量较常规施肥增产15.0%[11]。在掺有枯草芽孢杆菌的微生物肥料对土壤氮素流失的研究中也发现类似地结果，与单施尿素相比，枯草芽孢杆菌替代50%尿素可降低NH3的挥发，减少54%的土壤氮素流失，氮肥利用效率提高11.2%，作物产量提高5.0%[12-13]。施用微生物肥料还能提高作物品质，如添加Rhodopseudomonas spp. BL6和KL9能刺激番茄代谢活动，促进番茄果实重量和番茄红素含量的增加[14]。施用生物有机肥不仅能提高藜麦作物的产量及其种子的品质（如蛋白质、油脂等），还可以减少化学氮肥的使用。其残留效应还表现在随后两个生长季的锦葵产量都有所提高[15]。长期以来，农业生产者只重视作物的产量和生理健康，忽视了土壤健康这一基础性因素，过度使用化肥和农药，造成土壤健康形势日益严峻。而生物有机肥的使用可使化学氮、磷肥料用量减少50%左右，同时提高作物产量[16]。此外，微生物在生长繁殖过程中存在竞争关系，有益菌占据根际生态位形成优势菌群，能有效降低有害菌群的数量，并可以通过分泌抗生素、溶解酶和细菌素等代谢物减轻病原菌的侵染[17]。由此可见，微生物肥料作为植物低成本可再生和环境友好型养分的重要来源，显示出巨大的潜力，是综合营养管理(Integrated Nutrient Management, INM)和综合植物营养系统(Integrated Plant Nutrition System, IPNS)的重要组成部分[18]。

2 PGPB次生代谢物的作用机制

在整个植物发育过程中，微生物与其环境共同进化，它们和寄主植物之间可以建立亲密的联系，而不伤害植物[19]。许多PGPB具有提高植物应对生物和非生物胁迫的作用，这些微生物被认为是制备微生物肥料的潜在菌种。它们可以通过植物激素、酶、小分子化合物等次级代谢物促进植物生长；也可以通过产生铁载体和抗生素等与植物病原体竞争，保持植物健康。尽管PGPB有多种作用机制促进植物生长和抗逆，但是微生物肥料在使用过程中仍存在效果稳定性差、作用机理不明、菌肥产品与菌株同质化严重等问题。因此，为了更好地开发和应用微生物菌肥，有必要了解微生物促进植物生长的机制。如果能破译出介导这一过程的“关键代谢物”，并了解它们如何对植物发挥作用，这可能会为未来可持续农业发展提供更科学的理论指导信息。

2.1 微生物次生代谢物-可溶性化合物对植物生长的影响

传统上，人们对微生物代谢的研究多集中在可溶性化合物上，PGPB释放的这些可溶性化合物是公认的基石代谢物，因为它们具有多种多样的化学特性。有些菌株可以分泌有机分子，植物从这些分子中直接获得生长所需的资源，如植物可以利用有机碳作为碳源[20]。植物也能吸收尿素衍生物，如N-苄基-N-异丙基-N'-[4-(三氟甲氧基)苯基]尿素，可作为氮素的储备[21]。有些PGPB可以产生植物激素或酶类（如ACC脱氨酶、β-1,3葡聚糖酶和苯丙氨酸解氨酶等）[22]。如Pantoea agglomerans C1可诱导西洋梨的根系提前萌发，以及根系形态参数和根系构型的变化，这些变化依赖于该菌株释放的生长素样分子和其他代谢产物[23]。Bacillus rhizobacteria CSR-D4通过分泌防御相关的酶，如β-1,3葡聚糖酶、多酚氧化酶和苯丙氨酸解氨酶等，介导对尖孢镰刀菌的生防作用，间接促进植物生长[24]。也有大量的实验支持PGPB在逆境条件下可以改善植物生长发育并提高产量。耐盐根际细菌产生的次生代谢产物如胞外多糖、调节渗透溶质（脯氨酸、海藻糖和甜菜碱等），通过几种机制提高植物适应盐碱胁迫。如通过SOS1基因调节植物的细胞反应[25]；提高植物应激调节基因的表达[26]、高亲和力K+转运蛋白(HKT1)基因的表达[27]；增加抗氧化蛋白和乙烯生物合成等[28]参与缓解盐胁迫。一种由Bradyrhizobium和Bacillus brasiliensis组成的有益菌群与富含脂壳寡糖的根瘤菌代谢产物配合使用，不仅提高了大豆植株的净光合速率(17.7%)、气孔导度(56.5%)和蒸腾速率 (44%)，有效缓解了干旱期的氧化损伤。此外，该组合还可提高大豆结瘤率、植株生长发育和籽粒产量[29]。近年来，研究发现皮乐菌素、乙酰丁二醇(Acetylbutanediol, ABD)、艰难素、风霉素、表面素和吩嗪类等一些新型次生代谢物也参与植物的防病促生。Bacillus velezensis WRN031产生的3S, 4R-ABD和3R, 4R-ABD在植物根成熟区积累，参与调节玉米根系与有益菌的关系[30]。Bacillus amyloliquefaciens WS-8经基因组分析发现含有合成表面素、艰难素、风霉素等生物活性代谢物的基因簇可以刺激植物生长，并能产生伊枯草菌素和芬芥素抑制葡萄孢菌[31]。类似的结果在Pseudomonas aeruginosa RRLJ 04和Bacillus cereus bs03中也有发现，两种菌株产生的吩嗪衍生物对豌豆具有促进生长和防治枯萎病的作用[32]。总之，PGPB通过多种直接或间接机制保证植物营养元素的获取，从而改善作物的生长发育。

2.2 微生物代谢物-VOCs对植物生长的影响

近年来，越来越多的研究关注到微生物挥发性有机化合物(Volatile Organic Compounds, VOCs)。VOCs具有低沸点、高蒸汽压、易挥发、可跨越膜的特点，并可以通过空气、土壤和溶液从其起源地传递到很远的地方。这些特性使VOCs成为细胞间和组织间短期和长期连接的理想信号分子[33]。SuperScent数据库[34]中已收录2300种生物挥发性物质的信息。其中微生物挥发性有机化合物库(mVOC 2.0)包含604种细菌和340种真菌的1860种挥发性化合物的详细信息[35]。VOCs不是代谢废物，是微生物和植物之间的一种交流方式，并作为植物-微生物相互作用的营养和信息来源被开发。自2003年首次报道细菌挥发物促进植物生长以来，已有大量文献报道了微生物挥发物，其中主要以醛、酮和醇类最为丰富。研究较多的细菌挥发物包括2,3-丁二醇、二甲基二硫化物、乙偶姻、土臭素、吲哚等；真菌挥发物有6-戊基-2H-吡喃-2-酮、三甲胺、苯甲醛和二甲基辛胺等。这些化合物常被用于环境中微生物种类的特异性检测和微生物群落相互作用的标记[36-37]。其中许多被认为具有调节植物整体生长的潜力，它们在植物-微生物相互作用中主要从三个方面调节植物的生长：

（1）通过提高植物光合速率，渗透物、植物激素（生长素、细胞分裂素和赤霉素）和铁载体的合成等促进生长或改善品质。虽然PGPB释放的VOCs不含任何已知的植物生长激素或铁载体[38]，但有研究证实VOCs能够介导植物内源生长素稳态调控和根系对铁的吸收[39]。Bacillus subtilis SYST2产生的沙丁胺醇和1, 3-丙二醇通过调节番茄生长素、内源赤霉素、细胞分裂素和乙烯的水平刺激植物生长[40]。植物激素代谢和/或信号传导的刺激会导致植物根系结构的变化，这有助于水分和养分的吸收[41]。深绿木霉产生的戊基-2H-吡喃-2-酮(6-PP)具有促进植物生长，诱导侧根形成和调节根构型的作用，而根系对6-PP的响应涉及生长素转运和信号转导以及乙烯响应调节因子EIN2[42]。酵母能通过产生CO2促进草莓植株的光合作用，提高其果实中的糖含量，进而提高了3(2H)-呋喃酮、4-甲氧基-2,5-二甲基(DMMF)和苯丙氨酸衍生挥发物的含量，对草莓香气的提高具有积极作用[43]。也有研究发现VOCs可以抵消碳水化合物和脱落酸(ABA)介导的光合作用抑制，从而提高CO2同化效率并刺激植物生长发育[44]。

（2）VOCs可以提高植物对非生物胁迫的耐受性。据报道，Paraburkholderia phytofirmans PsJN能够促进多种植物宿主的生长，提高其对低温、干旱和盐度的耐受性。PsJN产生的2-十一烷酮、7-己醇和3-甲基丁醇不仅有助于改善植物受到的盐胁迫，而且还能促进拟南芥在高盐条件下的生长[45]。Alcaligenes faecalis JBCS1294产生的丁酸、丙酸和苯甲酸的混合物通过调节拟南芥生长素和赤霉素通路以及上调关键离子转运蛋白的表达促进植物的生长，并诱导拟南芥的耐盐性[46]。VOCs也可以增强拟南芥根中质膜H+-ATPase的活性，提高拟南芥的根际酸化能力，从而提高拟南芥对盐胁迫的耐受性[47]。气孔是植物与外界进行气体交换的重要途径，它的开合影响植物的光合效率和耐旱性。研究发现Pseudomonas chlororaphis O6产生的2,3-丁二醇通过脱落酸(ABA)、水杨酸(SA)、乙烯(ET)和茉莉酸(JA)信号通路诱导气孔的关闭，从而增加植物对干旱的耐受性[48]。

（3）VOCs还可以直接诱导植物通过茉莉酸/乙烯介导的诱导系统抗性(Induced Systemic Resistance, ISR)和水杨酸介导的系统获得抗性(Systemic Acquired Resistance, SAR)，防御启动是植物获得对多种植物病原菌免疫的有效机制[49]。早期诱导抗性的实验表明，低浓度的SA不能触发植物抗性，但改变了防御相关基因的表达，SA信号转导途径依赖一个功能基因NPR1[50]。与SA信号通路一样，JA在调节PGPB触发的防御机制中的作用已在JA/ET缺失突变体上得到初步确认[40]。在微型温室中，暴露于10 μL 2,3-丁二醇挥发物的黄瓜幼苗，其生长状况明显优于对照组，同时2,3-丁二醇通过激活JA信号通路诱导系统抗性[51]。Bacillus cereus AR156释放的VOCs可通过NPR1/JA/ET依赖途径在拟南芥中触发对Botrytis cinerea的ISR应答，这个过程依赖JA/ET信号通路和npr1[52]。尽管不同基因组在SA依赖的SAR通路和JA/ET依赖的ISR通路中表达存在差异，但在SAR中，JA和ET通路之间存在一定程度的沟通[53-54]。值得注意的是，在SAR中，发病相关基因的激活需要ET和JA两种信号转导，然而，其他的反应仅由其中一种受体促进[55]。目前通过真菌抑制试验发现，VOCs是抑制病原体的重要因子，正受到越来越多的关注[56]。

与其他代谢物相比，VOCs 因其作用模式而与众不同，它们可以通过水溶液扩散并渗透到大气中。这意味着VOCs不仅可以在地上起作用，而且还可以在地下起作用，其有效范围更大[57]。植物甚至不需要直接或长时间暴露在VOCs中，只是短暂的暴露其中也会刺激植物生长。这无疑为应用微生物菌剂促进作物的生长和产量，增强作物的系统抗性，维持农田生态系统的稳定，解决当前诸如化肥过度使用、作物产量和质量下降等农业问题提供了可行策略。

3 微生物肥料面临的挑战

3.1 高效菌种资源的挖掘与筛选

目前对于微生物肥料市场应用多集中在有限的种类上，如根瘤菌、芽孢杆菌、酵母菌等部分菌种，在所有微生物肥料产品中，芽孢杆菌的使用率达到80%以上，菌肥产品和菌株同质化现象严重[7]。虽然中国也在大力挖掘微生物资源，并建立了数个核心菌种库，然而优势菌种资源仍需提升。整合土壤微生物促进植物生长，消除或减少化肥的施用，高度依赖于对潜在、高效微生物菌株的筛选、优化及其代谢产物的分析。随着生物技术的进一步发展，通过物理诱变、化学诱变和基因组编辑方法获得品质优良的菌株已成为可能。通常认为代谢物是由单个生物体（如细菌细胞）产生和释放的最终产物，当应用两种及以上微生物菌种时，其代谢化合物之间可能会发生化学反应。最近的一项研究证实了这一推测，试验同时单独培养Serratia plymuthica 4Rx13和Staphylococcus delphini 20771，两者释放的VOCs前体经非酶性反应最终形成新的挥发性次级代谢产物[58]，这一发现突出了微生物之间相互作用的复杂性。虽然这为微生物菌种的筛选带来更多的挑战，但也是挖掘更多菌种组合的机遇。

3.2 微生物肥料在实际应用中的挑战

微生物肥料在使用过程中存在产品效果不稳定的问题，这与微生物肥料应用的制约因素和微生物作用机理认识不够深入有关。微生物肥料成功的关键在于菌种能在植物根际稳定定殖，并产生次级代谢产物，这便要求菌种具有普适性或者作为经济作物专用菌肥。然而微生物肥料的研究多集中在小麦、玉米、番茄、辣椒等部分作物，这些微生物肥料可能不适用于其他新兴经济作物。土壤肥力状况、pH值、有毒元素也会影响微生物的生长和对作物的响应。如气温升高可能会导致严重的干旱，不仅影响作物的生长发育，也会影响PGPB的性能[59]。此外，微生物产生的VOCs不仅仅对农作物起作用，对杂草的生长可能也有促进作用，并且在空旷的环境下，无法保证VOCs的浓度。而在实际应用中，微生物肥料的功能和使用技术未普及到普通农户，并且微生物肥料不像化肥能快速见效。因此，从实验室到田间应用，微生物的接种需要更多的研究、管理实践和详细的市场分析和调查，才能进入农业领域。同时了解不同的作用机制有助于菌株之间的不同组合，以普适性更广泛的微生物肥料提高作物产量。

4 展望

微生物肥料中含有大量活菌，可以帮助植物吸收养分，提高植物的耐受性，改善土壤结构，抑制病原菌，促进植物生长和作物品质[60]。微生物肥料对植物的作用主要依赖于它们产生的次级代谢产物，但关于有益微生物、次生代谢物、土壤性质、植物寄主之间的关系依旧扑朔迷离。首先，目前大多数的研究主要集中在模式植物和有限的微生物种类上，缺乏广泛适应性。其次，次生代谢物介导的作用机制随着研究的不断深入正在被逐步揭晓，但仍存在许多未解之谜。诸如，许多文献报道了VOCs作为空气信号影响激素变化、应激反应和宿主反应的潜在作用。但哪些微生物能产生有益代谢产物，该如何引导或刺激微生物释放有益的代谢物?植物是如何感知细菌挥发性代谢产物?怎样在田间保证VOCs浓度，并区别作物与杂草?了解和利用有益微生物的有益代谢产物是未来作物改良工作的关键，这些问题的解决对微生物肥料的发展有重要的推动作用。因此，可以从以下几个方面展开研究。

（1）加强高效功能菌株的筛选，结合高通量测序技术和培养组学技术，从微生物生长角度筛选功能菌株，确保菌株能快速适应作物，并在作物中定殖。

（2）探究微生物之间的相互作用关系，并基于它们之间的互作关系开发微生物之间新的组合技术，实现功能菌株在作物生长和抗逆功能上的“叠加或互补”。

（3）微生物代谢物是微生物影响作物生长的重要因素，微生物定殖并发挥作用受多种因素影响，这也导致微生物肥料稳定性差，在微生物肥料中添加微生物代谢物可能有助于微生物肥料的稳定性。但微生物本身的代谢物产量较低，而人工基因操纵子组装系统可以通过化学修饰优化和控制特定的代谢途径，在功能微生物中引入人工基因簇，可以增加目标代谢物的合成[61]。

（4）探究植物对微生物次级代谢产物的应答机制，将更好的为微生物肥料及其代谢产物发挥作用提供指导意见。

=2" class="main_content_center_left_zhengwen_bao_erji_title main_content_center_left_one_title" style="font-size: 16px;">{{custom_sec.title}}{{custom_sec.content}}[1]THOMAS G

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MAFFEI M E

. Bioprospecting bacterial and fungal volatiles for sustainable agriculture[J]. Trends in plant science, 2015, 20(4):206-211.

Current agricultural practice depends on a wide use of pesticides, bactericides, and fungicides. Increased demand for organic products indicates consumer preference for reduced chemical use. Therefore, there is a need to develop novel sustainable strategies for crop protection and enhancement that do not rely on genetic modification and/or harmful chemicals. An increasing body of evidence indicates that bacterial and fungal microbial volatile organic compounds (MVOCs) might provide an alternative to the use of chemicals to protect plants from pathogens and provide a setting for better crop welfare. It is well known that MVOCs can modulate the physiology of plants and microorganisms and in this Opinion we propose that MVOCs can be exploited as an ecofriendly, cost-effective, and sustainable strategy for agricultural practices. Copyright © 2015 Elsevier Ltd. All rights reserved.

SCHMIDT U

STRUCK S

, et al. SuperScent-a database of flavors and scents[J]. Nucleic acids research, 2009, 37(1):291-294.

GOHLKE B O

TOGUEM S M T

, et al. mVOC 2.0: a database of microbial volatiles[J]. Nucleic acids research, 2018, 46(D1):1261-1265.

Metabolic capabilities of microorganisms include the production of secondary metabolites (e.g. antibiotics). The analysis of microbial volatile organic compounds (mVOCs) is an emerging research field with huge impact on medical, agricultural and biotechnical applied and basic science. The mVOC database (v1) has grown with microbiome research and integrated species information with data on emitted volatiles. Here, we present the mVOC 2.0 database with about 2000 compounds from almost 1000 species and new features to work with the database. The extended collection of compounds was augmented with data regarding mVOC-mediated effects on plants, fungi, bacteria and (in-)vertebrates. The mVOC database 2.0 now features a mass spectrum finder, which allows a quick mass spectrum comparison for compound identification and the generation of species-specific VOC signatures. Automatic updates, useful links and search for mVOC literature are also included. The mVOC database aggregates and refines available information regarding microbial volatiles, with the ultimate aim to provide a comprehensive and informative platform for scientists working in this research field. To address this need, we maintain a publicly available mVOC database at: http://bioinformatics.charite.de/mvoc.© The Author(s) 2017. Published by Oxford University Press on behalf of Nucleic Acids Research.

SCHÜTZ E

GEH S

. Detection of microbial volatile organic compounds (MVOCs) produced by moulds on various materials[J]. International journal of hygiene and environmental health, 2001, 204(2-3):111-121.

Twelve fungal species were screened for microbial volatile organic compounds (MVOCs): Aspergillus fumigatus, A. versicolor, A. niger, A. ochraceus, Trichoderma harzianum, T. pseudokoningii, Penicillium brevicompactum, P. chrysogenum, P. claviforme, P. expansum, Fusarium solani and Mucor sp. More than 150 volatile substances derived from fungal cultures have been analysed by head-space solid-phase microextraction (HS-SPME). Each species had a defined MVOC profile which may be subjected to considerable modification in response to external factors such as cultivation on different substrata. The cultivation on different substrata changes the number and concentration of MVOCs. Species-specific volatiles may serve as marker compounds for the selective detection of fungal species in indoor environments. Examination of MVOCs from indoor air samples may become an important method in indoor air hygiene for the detection of type and intensity of masked contamination by moulds.

GITELSON I I

. The role of volatile metabolites in microbial communities of the LSS higher plant link[J]. Advances in space research, 2006, 38(6):1227-1232.

MALNOY M

MAFFEI M E

. Chemical diversity of microbial volatiles and their potential for plant growth and productivity[J]. Frontiers in plant science, 2015, 6:151.

Microbial volatile organic compounds (MVOCs) are produced by a wide array of microorganisms ranging from bacteria to fungi. A growing body of evidence indicates that MVOCs are ecofriendly and can be exploited as a cost-effective sustainable strategy for use in agricultural practice as agents that enhance plant growth, productivity, and disease resistance. As naturally occurring chemicals, MVOCs have potential as possible alternatives to harmful pesticides, fungicides, and bactericides as well as genetic modification. Recent studies performed under open field conditions demonstrate that efficiently adopting MVOCs may contribute to sustainable crop protection and production. We review here the chemical diversity of MVOCs by describing microbial plants and microbial microbial interactions. Furthermore, we discuss MVOCs role in inducing phenotypic plant responses and their potential physiological effects on crops. Finally, we analyze potential and actual limitations for MVOC use and deployment in field conditions as a sustainable strategy for improving productivity and reducing pesticide use.

ZHANG H

RYU C M

. Dynamic chemical communication between plants and bacteria through airborne signals: induced resistance by bacterial volatiles[J]. Journal of chemical ecology, 2013, 39(7):1007-1018.

Certain plant growth-promoting rhizobacteria (PGPR) elicit induced systemic resistance (ISR) and plant growth promotion in the absence of physical contact with plants via volatile organic compound (VOC) emissions. In this article, we review the recent progess made by research into the interactions between PGPR VOCs and plants, focusing on VOC emission by PGPR strains in plants. Particular attention is given to the mechanisms by which these bacterial VOCs elicit ISR. We provide an overview of recent progress in the elucidation of PGPR VOC interactions from studies utilizing transcriptome, metabolome, and proteome analyses. By monitoring defense gene expression patterns, performing 2-dimensional electrophoresis, and studying defense signaling null mutants, salicylic acid and ethylene have been found to be key players in plant signaling pathways involved in the ISR response. Bacterial VOCs also confer induced systemic tolerance to abiotic stresses, such as drought and heavy metals. A review of current analytical approaches for PGPR volatile profiling is also provided with needed future developments emphasized. To assess potential utilization of PGPR VOCs for crop plants, volatile suspensions have been applied to pepper and cucumber roots and found to be effective at protecting plants against plant pathogens and insect pests in the field. Taken together, these studies provide further insight into the biological and ecological potential of PGPR VOCs for enhancing plant self-immunity and/or adaptation to biotic and abiotic stresses in modern agriculture.

GU Q

WU H

, et al. Plant growth promotion by volatile organic compounds produced by Bacillus subtilis SYST2[J]. Frontiers in microbiology, 2017, 8:171.

GROENHAGEN U

SCHULZ S

, et al. The inter-kingdom volatile signal indole promotes root development by interfering with auxin signaling[J]. The plant journal, 2014, 80(5):758-771.

BARRERA-ORTIZ S

MUÑOZ-PARRa E

, et al. The volatile 6-pentyl-2H-pyran-2-one from Trichoderma atroviride regulates Arabidopsis thaliana root morphogenesis via auxin signaling and ETHYLENE INSENSITIVE 2 functioning[J]. New phytologist, 2016, 209(4):1496-1512.

PENG L

ZHANG H

, et al. Microbial biofertilizers increase fruit aroma content of Fragaria ananassa by improving photosynthetic efficiency[J]. Alexandria engineering journal, 2021, 60(6):5323-5330.

XIE X T

KIM M S

, et al. Soil bacteria augment Arabidopsis photosynthesis by decreasing glucose sensing and abscisic acid levels in planta[J]. The plant journal, 2008, 56(2):264-273.

ROJAS S

TIMMERMANN T

, et al. Volatile-mediated effects predominate in Paraburkholderia phytofirmans growth promotion and salt stress tolerance of Arabidopsis thaliana[J]. Frontiers in microbiology, 2016, 7:1838.

YU S M

LEE Y H

. Volatile compounds from Alcaligenes faecalis JBCS1294 confer salt tolerance in Arabidopsis thaliana through the auxin and gibberellin pathways and differential modulation of gene expression in root and shoot tissues[J]. Plant growth regulation, 2015, 75(1):297-306.

李菲, 石天龙, 唐明, 等. 促生细菌挥发性有机物调控根部质H+-ATPase活性提高植物耐碱胁迫能力[J]. 安徽农业大学学报, 2020, 47(4):594-598.

KANG B R

HAN S H

, et al. 2R,3R-butanediol, a bacterial volatile produced by Pseudomonas chlororaphis O6, is involved in induction of systemic tolerance to drought in Arabidopsis thaliana[J]. Molecular plant-microbe interactions, 2008, 21(8):1067-1075.

Root colonization of plants with certain rhizobacteria, such as Pseudomonas chlororaphis O6, induces tolerance to biotic and abiotic stresses. Tolerance to drought was correlated with reduced water loss in P. chlororaphis O6-colonized plants and with stomatal closure, indicated by size of stomatal aperture and percentage of closed stomata. Stomatal closure and drought resistance were mediated by production of 2R,3R-butanediol, a volatile metabolite of P. chlororaphis O6. Root colonization with bacteria deficient in 2R,3R-butanediol production showed no induction of drought tolerance. Studies with Arabidopsis mutant lines indicated that induced drought tolerance required the salicylic acid (SA)-, ethylene-, and jasmonic acid-signaling pathways. Both induced drought tolerance and stomatal closure were dependent on Aba-1 and OST-1 kinase. Increases in free SA after drought stress of P. chlororaphis O6-colonized plants and after 2R,3R-butanediol treatment suggested a primary role for SA signaling in induced drought tolerance. We conclude that the bacterial volatile 2R,3R-butanediol was a major determinant in inducing resistance to drought in Arabidopsis through an SA-dependent mechanism.

BECKERS G J M

FLORS V

, et al. Priming: getting ready for battle[J]. Molecular plant-microbe interactions, 2006, 19(10):1062-1071.

Infection of plants by necrotizing pathogens or colonization of plant roots with certain beneficial microbes causes the induction of a unique physiological state called "priming." The primed state can also be induced by treatment of plants with various natural and synthetic compounds. Primed plants display either faster, stronger, or both activation of the various cellular defense responses that are induced following attack by either pathogens or insects or in response to abiotic stress. Although the phenomenon has been known for decades, most progress in our understanding of priming has been made over the past few years. Here, we summarize the current knowledge of priming in various induced-resistance phenomena in plants.

KIM M S

SUN Y

, et al. Soil bacteria confer plant salt tolerance by tissue-specific regulation of the sodium transporter HKT1[J]. Molecular plant-microbe interactions, 2008, 21(6):737-744.

Elevated sodium (Na(+)) decreases plant growth and, thereby, agricultural productivity. The ion transporter high-affinity K(+) transporter (HKT)1 controls Na(+) import in roots, yet dysfunction or overexpression of HKT1 fails to increase salt tolerance, raising questions as to HKT1's role in regulating Na(+) homeostasis. Here, we report that tissue-specific regulation of HKT1 by the soil bacterium Bacillus subtilis GB03 confers salt tolerance in Arabidopsis thaliana. Under salt stress (100 mM NaCl), GB03 concurrently down- and upregulates HKT1 expression in roots and shoots, respectively, resulting in lower Na(+) accumulation throughout the plant compared with controls. Consistent with HKT1 participation in GB03-induced salt tolerance, GB03 fails to rescue salt-stressed athkt1 mutants from stunted foliar growth and elevated total Na(+) whereas salt-stressed Na(+) export mutants sos3 show GB03-induced salt tolerance with enhanced shoot and root growth as well as reduced total Na(+). These results demonstrate that tissue-specific regulation of HKT1 is critical for managing Na(+) homeostasis in salt-stressed plants, as well as underscore the breadth and sophistication of plant-microbe interactions.

RIU M

RYU C M

. Beyond the two compartments Petri-dish: optimising growth promotion and induced resistance in cucumber exposed to gaseous bacterial volatiles in a miniature greenhouse system[J]. Plant methods, 2019, 15(1):1-11.

LI X

WANG S

, et al. Induced systemic resistance against Botrytis cinerea by Bacillus cereus AR156 through a JA/ET-and NPR1-dependent signaling pathway and activates PAMP-triggered immunity in Arabidopsis[J]. Frontiers in plant science, 2017, 8:238.

ETALO D W

VAN DE MORTEL J E

, et al. Genome-wide analysis of bacterial determinants of plant growth promotion and induced systemic resistance by Pseudomonas fluorescens[J]. Environmental microbiology, 2017, 19(11):4638-4656.

SULTANA F

HYAKUMACHI M

. Role of ethylene signalling in growth and systemic resistance induction by the plant growth-promoting fungus Penicillium viridicatum in Arabidopsis[J]. Journal of phytopathology, 2017, 165(7-8):432-441.

MATHEW D C

HUANG C C

. Plant-microbe ecology: interactions of plants and symbiotic microbial communities[J]. Plant ecology-traditional approaches to recent trends, 2017:93-119.

WEISSKOPF L

. Mining the volatilomes of plant-associated microbiota for new biocontrol solutions[J]. Frontiers in microbiology, 2017, 8:1638.

Microbial lifeforms associated with land plants represent a rich source for crop growth-and health-promoting microorganisms and biocontrol agents. Volatile organic compounds (VOCs) produced by the plant microbiota have been demonstrated to elicit plant defenses and inhibit the growth and development of numerous plant pathogens. Therefore, these molecules are prospective alternatives to synthetic pesticides and the determination of their bioactivities against plant threats could contribute to the development of control strategies for sustainable agriculture. In our previous study we investigated the inhibitory impact of volatiles emitted by Pseudomonas species isolated from a potato field against the late blight-causing agent Phytophthora infestans. Besides the well-documented emission of hydrogen cyanide, other Pseudomonas VOCs impeded P infestans mycelial growth and sporangia germination. Current advances in the field support the emerging concept that the microbial volatilome contains unexploited, eco-friendly chemical resources that could help select for efficient biocontrol strategies and lead to a greener chemical disease management in the field.

CORDOVEZ V

DE BOER W

, et al. Volatile affairs in microbial interactions[J]. The isme journal, 2015, 9(11):2329-2335.

EFFMERT U

LEMFACK M C

, et al. Interspecific formation of the antimicrobial volatile schleiferon[J]. Scientific reports, 2018, 8:e16852.

GOLPAYEGANI A

. Effects of water stress and inoculation with plant growth promoting rhizobacteria (PGPR) on antioxidant status and photosynthetic pigments in basil (Ocimum basilicum L.)[J]. Journal of the saudi society of agricultural sciences, 2012, 11(1):57-61.

ANSARI M W

SAHOO R K

, et al. Biofertilizers function as key player in sustainable agriculture by improving soil fertility, plant tolerance and crop productivity[J]. Microbial cell factories, 2014, 13(1):1-10.

WESTRICH L

RÖSCH M

, et al. AGOS: a plug-and-play method for the assembly of artificial gene operons into functional biosynthetic gene clusters[J]. ACS synthetic biology, 2017, 6(5):817-825.

The generation of novel secondary metabolites by reengineering or refactoring biochemical pathways is a rewarding but also challenging goal of synthetic biology. For this, the development of tools for the reconstruction of secondary metabolite gene clusters as well as the challenge of understanding the obstacles in this process is of great interest. The artificial gene operon assembly system (AGOS) is a plug-and-play method developed as a tool to consecutively assemble artificial gene operons into a destination vector and subsequently express them under the control of a de-repressed promoter in a Streptomyces host strain. AGOS was designed as a set of entry plasmids for the construction of artificial gene operons and a SuperCos1 based destination vector, into which the constructed operons can be assembled by Red/ET-mediated recombination. To provide a proof-of-concept of this method, we disassembled the well-known novobiocin biosynthetic gene cluster into four gene operons, encoding for the different moieties of novobiocin. We then genetically reorganized these gene operons with the help of AGOS to finally obtain the complete novobiocin gene cluster again. The production of novobiocin precursors and of novobiocin could successfully be detected by LC-MS and LC-MS/MS. Furthermore, we demonstrated that the omission of terminator sequences only had a minor impact on product formation in our system.

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