微生物学通报  2023, Vol. 50 Issue (1): 13−34

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文章信息

朱攀, 薛文凯, 李小燕, 刘星
ZHU Pan, XUE Wenkai, LI Xiaoyan, LIU Xing
青藏高原垫状点地梅叶际及内生可培养微生物多样性
Diversity of phyllospheric and endophytic culturable microorganisms in Androsace tapete of the Qinghai-Tibetan Plateau
微生物学通报, 2023, 50(1): 13-34
Microbiology China, 2023, 50(1): 13-34
DOI: 10.13344/j.microbiol.china.220411

文章历史

收稿日期: 2022-04-21
接受日期: 2022-05-18
网络首发日期: 2022-07-04
青藏高原垫状点地梅叶际及内生可培养微生物多样性
朱攀1 , 薛文凯1 , 李小燕2 , 刘星1,2     
1. 西藏大学理学院 生态学研究中心极端环境生物资源与适应性进化实验室, 西藏  拉萨    850000;
2. 武汉大学生命科学学院, 湖北  武汉    430072
摘要: 【背景】 垫状点地梅作为青藏高原最具代表性的垫状植物,其叶际和内生微生物对适应极端环境有重要意义,同时也是一种独特的资源。【目的】 探究垫状点地梅叶际和叶内可培养微生物多样性,以及不同生存状态个体之间的微生物差异。【方法】 采用纯培养方法分离和纯化3个不同地区垫状点地梅叶际和叶内的细菌、酵母菌和丝状真菌,并用16S rRNA基因和ITS区域序列进行分析鉴定。【结果】 最终得到叶际微生物350株,鉴定为22属49种,优势种为Penicillium sajarovii;内生微生物274株,鉴定为19属45种,优势种为Bacillus mycoides;两者的优势属均为Penicillium。垫状点地梅叶际和叶内之间及不同生存状态个体之间微生物的α多样性大多无显著差异,各群落间的成员也有重叠,但物种组成存在显著的空间异质性。【结论】 垫状点地梅叶际和叶内有着丰富的可培养微生物资源,来源于不同生存状态的个体或不同部位的微生物物种组成差别较大,微生物对不同环境的选择偏好形成了不同的群落模式。但这些不同来源的微生物群落之间同样存在高比例的共有菌株,这些共有菌株的异养方式和生态位并不固定,可兼共生和腐生生存,生存空间也无明确的界限。纯化的菌株可为日后功能菌株的开发利用提供材料。
关键词: 青藏高原    垫状点地梅    叶际可培养微生物    内生可培养微生物    
Diversity of phyllospheric and endophytic culturable microorganisms in Androsace tapete of the Qinghai-Tibetan Plateau
ZHU Pan1 , XUE Wenkai1 , LI Xiaoyan2 , LIU Xing1,2     
1. Laboratory of Extreme Environment Biological Resources and Adaptive Evolution, Research Center for Ecology, College of Science, Tibet University, Lhasa 850000, Tibet, China;
2. College of Life Sciences, Wuhan University, Wuhan 430072, Hubei, China
Abstract: [Background] Androsace tapete is the representative cushion plant species on the Qinghai-Tibetan Plateau, and the phyllospheric and intrafoliar microorganisms are important for this species to adapt to the extreme environment and are also a unique resource. [Objective] To investigate the diversity of phyllospheric and endophytic culturable microorganisms in A. tapete and the differences in the microorganisms between living and dead individuals. [Methods] Phyllospheric and intrafoliar bacteria, yeasts, and filamentous fungi were isolated from A. tapete in three different regions by pure culture, purified, and identified based on 16S rRNA and ITS sequence analysis. [Results] A total of 350 phyllospheric strains (49 species in 22 genera) were identified, with the dominant species of Penicillium sajarovii, and 274 endophytic culturable strains (45 species in 19 genera) were screened out, with the dominant species of Bacillus mycoides. The two shared the dominant Penicillium. The difference in alpha diversity between phyllospheric and intrafoliar microorganisms of A. tapete and between the living and dead individuals was mostly not significant. The communities shared some members, but there was significant spatial heterogeneity in species composition. [Conclusion] There are abundant culturable phyllospheric and intrafoliar microbial resources in A. tapete, and the species composition was remarkably different between living and dead individuals and between different parts of the leaf, and the selection preferences of microorganisms for different environments result in different community patterns. However, the microbial communities from different sources shared a high proportion of strains, and the heterotrophic mode and ecological niche of these shared strains are not fixed. The heterotrophic pattern and the niches of the shared strains are not fixed. They can survive by both symbiosis and saprophytism, and the living space has no clear boundary. The purified strains can be used for the development and utilization of functional strains.
Keywords: Qinghai-Tibetan Plateau    Androsace tapete    phyllospheric culturable microorganism    endophytic culturable microorganism    

作为世界“第三极”的青藏高原是全球最大、最高的高原[1],其特殊的自然地理环境孕育了丰富而独特的生物多样性[2],这里脆弱的生态系统对气候变化和人类活动高度敏感,气温变暖、冰川融化等问题日益加剧[3-4]。青藏高原植物种类繁多,有着紧凑叶片、低矮莲座型的垫状植物是分布于高山地区的一类代表性植物[5]。其中,垫状点地梅(Androsace tapete)是报春花科(Primulaceae)点地梅属(Androsace L.)的垫状植物代表物种,所属的垫状点地梅群系是青藏高原垫状植被中分布最广、最重要的群系[6-7]

在植物的叶部存在着多样的微生物群落,其中附生在叶片表面的微生物称为叶际微生物,生活在植株内部的称为内生菌或内生微生物[8-9]。相较于已深入研究的植物根系和根际微生物,叶际和叶内的内生微生物对植物健康的影响和互作关系等方面的研究较少[10-11]。与植物互作的微生物被认为对植物的生长、抵御生物和非生物胁迫等方面具有重要意义,如叶际微生物群可以通过产生抗菌化合物、与病原菌竞争或介导激活植物防御来增强对病原体的抗性[12-14],还可以影响植物对养分的获取(如固氮作用)[15-16],以及对干旱、紫外线和抗冻性等非生物胁迫的适应[17-19]。叶片内生菌可通过特定代谢途径降解叶片表面吸收的污染物[20-21],改善受污染环境中的植物修复,以及提高在这些条件下的适应性(如抗旱能力)[22-24]。因此,叶际和内生微生物是一类特殊的菌种资源,在修复污染、推动植物宿主适应干旱和气候变暖,以及抵御病虫害等方面的应用有着巨大的潜力[25]。目前关于垫状点地梅的研究主要集中在其区系类型和分布格局[26-27]、形态适应性和生态系统工程师[28-30]、空间遗传结构[31]等方面。垫状点地梅微生物方面,已有研究表明垫状点地梅根际土壤细菌的主要菌门为厚壁菌门、变形菌门和放线菌门,环境因子中的大气温度与菌群相对丰度呈极显著正相关[32],但关于其地上部分的叶际和内生微生物方面还未见报道。垫状点地梅的叶片是其适应性垫状结构的重要组成部分,其极端的生境为分离出一些独特菌种提供了可能。本研究以青藏高原垫状点地梅的存活个体和死亡个体为材料,探究垫状点地梅叶际和内生可培养微生物的物种多样性(死亡个体叶片内的微生物严格意义上应称之为腐生菌,本文为与活体中内生菌对应,统一称为内生微生物),并比较其存活个体与死亡个体微生物物种组成的相似性和差异,以及叶际和内生可培养微生物物种组成的相似性和差异。实验纯化的菌株可进一步充实青藏高原种质资源库,并为日后功能菌株的开发利用提供材料。研究结果将为探明垫状点地梅非自然死亡的原因和对高原极端环境的适应性机制提供可培养微生物方面的数据信息。

1 材料与方法 1.1 材料

垫状点地梅样本采自西藏米拉山(编号为MLS)、恰拉山(编号为QLS)和卡若拉冰川(编号为KRL),3个样点的信息如表 1所示。每个样点采集垫状点地梅存活个体与死亡个体各3株,共18株。戴无菌手套和口罩将垫状点地梅整株挖起,抖落根部附着的土后,放入大号无菌均质袋中,置于4 ℃车载冰箱中暂存,最后带回实验室放入4 ℃冰箱备用,开始菌株的分离实验。

表 1 采样点信息 Table 1 Information of sampling sites
Site Longitude and latitude Altitude (m) Air temperature (℃) Air humidity (%) Light intensity (lx)
Mila Mountain (MLS) E 92.365 032°
N 29.817 694°
4 900 15.4 46.4 42 956
Qiala Mountain (QLS) E 91.275 797°
N 30.113 067°
4 767 13.3 28.3 12 008
Karola Glacier (KRL) E 90.224 676°
N 28.898 962°
4 789 16.7 9.1 19 478

细菌基因组DNA抽提试剂盒和Taq Master Mix,生工生物工程(上海)股份有限公司;16S rRNA基因通用引物1492R和27F、真菌核糖体rDNA区通用引物ITS1和ITS4,南京诺唯赞生物科技股份有限公司。PCR仪和电泳仪,艾本德公司。

1.2 菌株的分离、纯化及鉴定

1.2.1 材料的处理

将3个样点的18个垫状点地梅样本各取5 g叶片组织,放入盛有50 mL无菌水的无菌EP管中,摇床室温200 r/min振荡水洗30 min[33-34],得到的菌悬液用稀释梯度法稀释101−106倍,用于叶际微生物的分离和纯化。另取各垫状点地梅叶片5 g,在超净工作台内用75%酒精浸泡30 s后漂洗、3%次氯酸钠浸泡60 s后漂洗,循环3次,对叶片的表面杀菌,再用无菌水洗涤3次(取最后一次漂洗液0.1 mL涂布到牛肉膏蛋白胨培养基平板上,28 ℃恒温培养72 h,检测表面消毒效果),最后将材料剪碎研磨稀释10倍备用。

1.2.2 培养基

细菌使用牛肉膏蛋白胨培养基(g/L):牛肉膏3.0,蛋白胨10.0,NaCl 5.0,琼脂20.0,pH 7.0,98 kPa灭菌30 min。真菌使用酸性PDA、酸性YM及RBCH固体常规培养基,参照文献[35]配制。

1.2.3 菌株的分离与纯化

取各样本稀释液0.1 mL分别涂布到4种培养基平板上,分别做3个重复,于28 ℃恒温培养3−5 d。待平板长出菌落后,挑取单菌落四区划线至相同配方的平板中纯化。通过菌落形态初步将其分为细菌、酵母菌和丝状真菌3类,再用显微镜镜检进一步区分三者。在试管斜面上纯化菌株(若平板上出现杂菌污染,则需多次四区划线纯化,直至得到单一菌落),最后用20%甘油保藏于−80 ℃冰箱中。

1.2.4 菌株的鉴定

细菌DNA的提取和扩增使用细菌基因组DNA抽提试剂盒,引物为16S rRNA基因通用引物27F (5′-AGAGTTTGATCCTGGCTCAG-3′)和1492R (5′-GGTTACCTTGTTACGCTT-3′)。PCR反应体系:2×PCR Taq Master Mix 25 µL,正、反向引物(10 µmol/L)各2 µL,细菌DNA 5 µL,超纯水21 µL。PCR反应条件:94 ℃ 4 min;94 ℃ 30 s,55 ℃ 30 s,72 ℃ 90 s,35个循环;72 ℃ 10 min。真菌DNA的提取及扩增采用CTAB法[36],引物采用ITS1 (5′-TCCGTAGGTGAACCTGCGG-3′)和ITS4 (5′-TCCTCCGCTTATTGATATGC-3′)[37]。PCR反应体系:2×PCR Taq Master Mix 25 µL,ITS1和ITS4引物(10 µmol/L)各2.5 µL,真菌DNA 5 µL,超纯水20 µL。PCR反应条件:95 ℃ 5 min;95 ℃ 30 s,55 ℃ 30 s,72 ℃ 60 s,35个循环;72 ℃ 7 min。经1.5%琼脂糖凝胶电泳检测后,将浓度和大小合格的扩增目标产物送往生工生物工程(上海)股份有限公司测序。测序结果经BioEdit人工校对去除引物及双峰序列后,在GenBank核酸序列数据库中进行同源序列搜索,BLAST结果相似度为99%以上的确定为同一种[38],丝状真菌的鉴定需结合显微形态判断。供试菌株的序列提交到国家微生物科学数据中心(National Microbiology Data Center, NMDC),细菌DOI为NMDCN00010M9和NMDCN 00010MA−NMDCN00010MV,真菌DOI为NMDCN00010N0−NMDCN00010N9、NMDCN 00010NA−NMDCN00010NV和NMDCN00010O0−NMDCN00010O3。

1.3 数据的处理及分析

使用Excel 2016、R 4.0.2、Origin 2018等软件分析数据及绘图。非度量多维尺度(non- metric multidimensional scaling, NMDS)分析、相似性(analysis of similarities, ANOSIM)分析、α多样性Richness物种丰富度、Shannon-Wiener多样性指数、Simpson多样性指数、Pielou均匀度指数、invsimpson指数、Chao1菌种丰富度指数、ACE指数、goods_coverage指数用R 4.0.2中的vegan包进行计算,ggplot2包绘图。Pearson相关系数用psych包计算,pheatmap包绘图。相对丰度是指某样本中某种菌的菌株数占该样本总菌株数的百分比。

2 结果与分析 2.1 垫状点地梅叶际可培养微生物多样性

2.1.1 垫状点地梅叶际可培养微生物的物种组成和分布

图 1所示,从18个垫状点地梅样本中共分离、纯化出叶际微生物350株,22属49种,其中,细菌100株,10属18种;酵母菌50株,5属8种;丝状真菌200株,7属23种。各样点的叶际微生物物种组成比较丰富,其中恰拉山的物种组成最复杂,有128株,35种;其次是米拉山103株,31种;最后为卡若拉119株,28种。

图 1 垫状点地梅叶际可培养微生物在各样点的组成和分布 Figure 1 Composition and distribution of phyllospheric culturable microorganisms of Androsace tapete at each site. Alive代表垫状点地梅的存活个体;Dead代表垫状点地梅的死亡个体;QLS、KRL、MLS分别代表采样点恰拉山、卡若拉和米拉山 Alive: The surviving individuals of Androsace tapete; Dead: The dead individuals of Androsace tapete; QLS, KRL and MLS: Sampling sites Qiala Mountain, Karuola and Mila Mountain, respectively.

为进一步探究垫状点地梅叶际微生物的优势类群,对各样本的所有菌株丰度进行分析。如图 2所示,在种水平上相对丰度前5的菌株依次为Penicillium sajarovii (9.14%)、Fusarium tricinctum (7.43%)、Fusarium acuminatum (6.29%)、Pseudomonas baetica (5.43%)和Pseudomonas koreensis (5.14%),其中前3种均为丝状真菌,后2种为细菌,Penicillium sajarovii丰度最高,为优势种。如图 3所示,在属水平上相对丰度前5的属依次为Penicillium (23.71%)、Fusarium (17.71%)、Pseudomonas (15.71%)、Cladosporium (9.43%)和Naganishia (5.43%),共计丰度为72.00%,Penicillium丰度最高,为优势属。

图 2 垫状点地梅叶际可培养微生物种水平的相对丰度 Figure 2 Relative abundance of phyllospheric culturable microorganisms at the species level in the Androsace tapete. Others为相对丰度低于1%的菌种 Others are species with relative abundance less than 1%.

图 3 垫状点地梅叶际可培养微生物属水平的相对丰度 Figure 3 Relative abundance of phyllospheric culturable microorganisms at the genus level in the Androsace tapete. Others为相对丰度低于1%的属 Others are genera with relative abundance less than 1%.

2.1.2 垫状点地梅存活与死亡个体叶际可培养微生物间α多样性的比较

为探究垫状点地梅存活与死亡个体间叶际可培养微生物多样性的差异,以α多样性指数对存活与死亡个体的叶际微生物进行比较。结果如图 4所示,垫状点地梅死亡个体除goods_ coverage指数外,其余7种多样性指数的均值都高于存活个体,但二者间的差异并不显著(P > 0.05)。表明垫状点地梅死亡和存活个体叶际微生物的多样性都较高,但并无显著差异。

图 4 垫状点地梅存活与死亡个体叶际微生物间α多样性指数比较 Figure 4 Comparison of phyllospheric microorganisms alpha diversity index between alive and dead individuals of Androsace tapete. PM-A (phyllospheric microganism-alive):垫状点地梅存活个体的叶际微生物;PM-D (phyllospheric microganism-dead):垫状点地梅死亡个体的叶际微生物 PM-A (phyllospheric microganism-alive): The phyllospheric microorganisms of surviving individuals in Androsace tapete; PM-D (phyllospheric microganism-dead): The phyllospheric microorganisms of dead individuals in Androsace tapete.

2.1.3 垫状点地梅存活与死亡个体间叶际可培养微生物的优势类群和独有菌株分析

表 2所示,垫状点地梅存活个体叶际可培养微生物独有的菌株共9种,其中细菌3种,相对丰度共计5.14%;酵母菌4种,相对丰度共计3.42%;丝状真菌2种,相对丰度共计1.71%。选存活个体中相对丰度前10的菌株为优势类群,其中细菌2种,相对丰度共计13.15%;酵母菌1种,相对丰度共计4.57%;丝状真菌7种,相对丰度共计45.13%。死亡个体独有的菌株共13种,其中细菌7种,相对丰度共计8.57%;丝状真菌6种,相对丰度共计10.28%。选死亡个体中相对丰度前10的菌株为优势类群,其中细菌2种,相对丰度共计10.29%;酵母菌3种,相对丰度共计14.86%;丝状真菌5种,相对丰度共计32.00%。

表 2 垫状点地梅存活与死亡个体间叶际可培养微生物的优势类群和独有菌株比较 Table 2 Comparison of dominant groups and unique strains of phyllospheric culturable microorganisms between alive and dead individuals of Androsace tapete
Strains unique to the
alive individuals
Dominant group of alive
individuals
Dominant group of dead
individuals
Strain unique to the dead individuals
Pseudomonas mandelii (2.29%)a Penicillium sajarovii (9.71%)c Penicillium sajarovii (8.57%)c Penicillium wellingtonense (4.00%)c
Pseudomonas helmanticensis (1.71%)a Penicillium raistrickii (7.43%)c Fusarium tricinctum (8.00%)c Brevibacterium frigoritolerans (2.29%)a
Pseudomonas poae (1.14%)a Pseudomonas baetica (6.86%)a Fusarium acuminatum (7.43%)c Paenarthrobacter aurescens (2.29%)a
Debaryomyces fabryi (1.14%)b Fusarium tricinctum (6.86%)c Naganishia adeliensis (6.86%)b Cladosporium pseudocladosporioides (2.29%)c
Debaryomyces hansenii (1.14%)b Pantoea agglomerans (6.29%)a Pseudomonas koreensis (6.29%)a Penicillium aurantiogriseum (1.71%)c
Fusarium oxysporum (1.14%)c Cladosporium subuliforme
(5.71%)c
Aureobasidium pullulans (4.57)b Penicillium solitum (1.14%)c
Mrakia aquatica (0.57%)b Cladosporium cladosporioides (5.14%)c Pseudomonas baetica (4.00%)a Peribacillus muralis (1.14%)a
Rhodotorula mucilaginosa (0.57%)b Fusarium acuminatum (5.14%)c Neurospora tetraspora (4.00%)c Rossellomorea oryzaecorticis (1.14%)a
Cladosporium tenuissimum (0.57%)c Penicillium griseoroseum
(5.14%)c
Penicillium wellingtonense
(4.00%)c
Bacillus toyonensis (0.57%)a
Mrakia cryoconiti (4.57%)b Mrakia cryoconiti (3.43%)b Chryseobacterium lactis (0.57%)a
Pseudomonas graminis (0.57%)a
Alternaria chlamydosporigena (0.57%)c
Asordaria humana (0.57%)c
abc分别表示细菌、酵母菌和丝状真菌;括号中的数为各菌株的相对丰度;−:无数据
a, b, c indicate bacteria, yeast and filamentous fungi respectively; The number in parentheses is the relative abundance of each strain; −: No data.

此外,垫状点地梅存活与死亡个体叶际可培养微生物共有菌株27种,相对丰度之和分别占89.73%和81.15%。因此,垫状点地梅存活与死亡个体的叶际可培养微生物在物种组成方面较为相似,独有菌株分别占10.27%和18.85%;而且在独有菌株中,除Penicillium wellingtonense是死亡个体优势类群外,其余独有菌株均无优势性。

2.2 垫状点地梅内生可培养微生物多样性

2.2.1 垫状点地梅内生可培养微生物的物种组成和分布

图 5所示,垫状点地梅样本中共分离、纯化出内生微生物274株,鉴定为19属45种,其中,细菌139株,9属18种;酵母菌22株,4属7种;丝状真菌113株,6属20种。各样点的内生微生物物种组成比较丰富,其中恰拉山84株,29种;卡若拉105株,28种;米拉山85株,23种。

图 5 垫状点地梅内生可培养微生物在各样点的组成和分布 Figure 5 Composition and distribution of endophytic culturable microorganisms of Androsace tapete at each site. Alive代表垫状点地梅的存活个体;Dead代表垫状点地梅的死亡个体;QLS、KRL、MLS分别代表采样点恰拉山、卡若拉和米拉山 Alive: The surviving individuals of Androsace tapete; Dead: The dead individuals of Androsace tapete; QLS, KRL and MLS: Sampling sites Qiala Mountain, Karuola and Mila Mountain, respectively.

图 6为垫状点地梅内生可培养微生物在种水平的丰度情况,相对丰度前5的菌株依次为Bacillus mycoides (7.30%)、Fusarium tricinctum (6.93%)、Pantoea agglomerans (6.93%)、Fusarium acuminatum (5.11%)和Pseudomonas baetica (5.11%),其中,Fusarium tricinctumFusarium acuminatum为丝状真菌,其余3种为细菌,Bacillus mycoides丰度最高为优势种。如图 7所示,在属水平上相对丰度前5的属依次为Penicillium (17.52%)、Fusarium (16.79%)、Pseudomonas (15.33%)、Bacillus (14.23%)和Pantoea (6.93%),共计丰度为70.80%,Penicillium丰度最高,为优势属。

图 6 垫状点地梅内生可培养微生物种水平的相对丰度 Figure 6 Relative abundance of endophytic culturable microorganisms at the species level in the Androsace tapete. Others为相对丰度低于1%的菌种 Others are species with relative abundance less than 1%.

图 7 垫状点地梅可培养内生微生物属水平的相对丰度 Figure 7 Relative abundance of endophytic culturable microorganisms at the genus level in the Androsace tapete. Others为相对丰度低于1%的属 Others are genera with relative abundance less than 1%.

2.2.2 垫状点地梅存活与死亡个体内生可培养微生物间α多样性比较

比较垫状点地梅存活与死亡个体间内生可培养微生物的α多样性指数,结果显示(图 8),垫状点地梅死亡个体除Chao1指数和ACE指数外,其他多样性指数的均值均高于存活个体,但二者的差异并不显著(P > 0.05)。

图 8 垫状点地梅存活与死亡个体内生微生物间α多样性指数比较 Figure 8 Comparison of endophytic microorganisms alpha diversity index between alive and dead individuals of Androsace tapete. EM-A (endophytic microganism-alive):垫状点地梅存活个体的内生微生物;EM-D (endophytic microganism-dead):垫状点地梅死亡个体的内生微生物 EM-A (endophytic microganism-alive): The endophytic microorganisms of surviving individuals in Androsace tapete; EM-D (endophytic microganism-dead): The endophytic microorganisms of dead individuals in Androsace tapete.

2.2.3 垫状点地梅存活与死亡个体间内生可培养微生物的优势类群和独有菌株分析

表 3所示,垫状点地梅存活个体内生可培养微生物独有的菌株共6种,均为细菌,相对丰度共计10.00%。选存活个体中相对丰度前10的菌株为优势类群,其中细菌5种,相对丰度共计40.00%;丝状真菌5种,相对丰度共计26.00%。死亡个体独有的菌株共14种,其中细菌4种,相对丰度共计13.22%;酵母菌4种,相对丰度共计4.01%;丝状真菌6种,相对丰度共计12.06%。选死亡个体中相对丰度前10的菌株为优势类群,其中细菌7种,相对丰度共计31.62%;丝状真菌3种,相对丰度共计17.25%。

表 3 垫状点地梅存活与死亡个体间内生可培养微生物的优势类群和独有菌株比较 Table 3 Comparison of dominant groups and unique strains of endophytic culturable microorganisms between alive and dead individuals of Androsace tapete
Strains unique to the alive individuals Dominant group of alive individuals Dominant group of dead individuals Strain unique to the dead individuals
Alternaria alternate (2.00%)a Bacillus mycoides (14.00%)a Fusarium tricinctum (8.05%)c Peribacillus simplex (6.90%)a
Cladosporium variabile (2.00%)a Pantoea agglomerans (11.00%)a Peribacillus simplex (6.90%)a Penicillium sajarovii (4.60%)c
Fusarium avenaceum (2.00%)a Pseudomonas baetica (8.00%)a Bacillus simplex (5.17%)a Penicillium griseoroseum (3.45%)c
Penicillium raistrickii (2.00%)a Fusarium acuminatum (6.00%)c Acinetobacter johnsonii (4.60%)a Pseudomonas graminis (2.87%)a
Peribacillus muralis (1.00%)a Fusarium oxysporum (6.00%)c Pantoea agglomerans (4.60%)a Brevibacterium frigoritolerans (2.30%)a
Paraburkholderia fungorum (1.00%)a Cladosporium cladosporioides (5.00%)c Fusarium acuminatum (4.60%)c Penicillium goetzii (2.30%)c
Fusarium tricinctum (5.00%)c Penicillium sajarovii (4.60%)c Debaryomyces prosopidis (1.72%)b
Pseudomonas sp. (4.00%)a Bacillus mycoides (3.45%)a Pseudomonas mandelii (1.15%)a
Penicillium aurantiogriseum (4.00%)c Bacillus butanolivorans (3.45%)a Debaryomyces fabryi (1.15%)b
Acinetobacter johnsonii (3.00%)a Pseudomonas baetica (3.45%)a Mrakia aquatic (0.57%)b
Naganishia adeliensis (0.57%)b
Alternaria chlamydosporigena (0.57%)c
Asordaria humana (0.57%)c
Fusarium petersiae (0.57%)c
a:细菌;b:酵母菌;c:丝状真菌;括号中的数为各菌株的相对丰度;−:无数据
a: Bacteria, b: Yeast; c: Filamentous fungi; The number in parentheses is the relative abundance of each strain; −: No data.

此外,垫状点地梅存活与死亡个体内生可培养微生物共有菌株25种,相对丰度之和分别占90.00%和70.71%。因此,垫状点地梅存活与死亡个体的内生可培养微生物大部分较为相似,独有菌株分别只占10.00%和29.29%。在死亡个体独有的菌株中,Peribacillus simplex (6.90%)、Penicillium sajarovii (4.60%)、Penicillium griseoroseum (3.45%)属于死亡个体优势类群,存活个体独有菌株均无优势性。

2.3 垫状点地梅叶际与内生可培养微生物

2.3.1 垫状点地梅叶际与内生可培养微生物间的物种组成相关性

将各垫状点地梅样本的物种组成特征进行相关性分析并绘制聚类热图,结果如图 9所示,各样本间的Pearson相关性系数均为正相关。聚类和显著性标记表明,3个样点的内生和叶际可培养微生物,其存活和死亡个体间物种组成的差异并不显著。而内生微生物和叶际微生物分别聚类在一起,显著性标记同样表明二者内部的物种组成相关性更为显著。综上可知,垫状点地梅的存活与否对其物种组成特征而言并无显著影响,而不同的生存空间造就了垫状点地梅叶际与内生可培养微生物的组成差异。

图 9 垫状点地梅各样点菌种组成的Pearson相关性聚类热图 Figure 9 Pearson correlation clustering heat map of species composition in Androsace tapete at each site. QLS、KRL、MLS分别代表采样点恰拉山、卡若拉和米拉山;PM:垫状点地梅叶际微生物(phyllospheric microganism);EM:垫状点地梅内生微生物(endophytic microganism);A:垫状点地梅存活个体(alive);D:垫状点地梅死亡个体(dead) QLS, KRL, MLS: Sampling sites Qiala Mountain, Karuola and Mila Mountain respectively; PM: The interleaf microorganisms of the Androsace tapete (phyllospheric microganism); EM: The endophytic microorganisms of the Androsace tapete respectively (endophytic microganism); A: The surviving individuals of the Androsace tapete (alive); D: The dead individuals of the Androsace tapete (dead).

2.3.2 垫状点地梅叶际与内生可培养微生物间α多样性比较和物种组成空间变异分析

比较垫状点地梅叶际与内生可培养微生物的α多样性指数,结果如图 10所示,垫状点地梅叶际可培养微生物除Pielou均匀度指数和goods_coverage指数外,其余多样性指数的均值均高于内生可培养微生物,其中叶际可培养微生物的Chao1指数显著高于内生可培养微生物(P=0.041),其余多样性指数差异并不显著(P > 0.05)。

图 10 垫状点地梅叶际与内生可培养微生物α多样性指数的比较 Figure 10 Comparison of phyllospheric and endophytic culturable microorganisms alpha diversity index in Androsace tapete.

虽然垫状点地梅叶际与内生可培养微生物α多样性间的差异并不显著,但聚类热图结果显示,两者在物种组成上存在差异,将两者分组,用基于Bray-Curtis距离做非度量多维尺度(NMDS)和ANOSIM分析。结果表明(图 11A),垫状点地梅叶际与内生可培养微生物的物种组成存在差异,响应压力值Stress=0.128 1,置信椭圆有一定的重合但仍能较好地对二者进行区分。ANOSIM分析(图 11B)表明组内差异显著小于组间差异(R=0.562,P < 0.01),即垫状点地梅叶际和叶内微生物的群落结构存在显著的空间异质性。

图 11 垫状点地梅叶际和内生微生物物种组成的空间变异分析Between为垫状点地梅叶际和内生微生物组间的差异 Figure 11 Analysis of spatial variation of phyllospheric and endophytic microbial species composition in Androsace tapete. A:NMDS分析. B:ANOSIM分析. A: NMDS analysis. B: ANOSIM analysis. Between is the difference between the phyllospheric and endophytic microganism of Androsace tapete.

2.3.3 垫状点地梅叶际与内生可培养微生物间物种组成分析

多集合韦恩图显示(图 12),垫状点地梅叶际与内生可培养微生物间共有物种有35种(13种细菌、6种酵母菌、16种丝状真菌),叶际与内生独有的菌株分别有14种(5种细菌、2种酵母菌、7种丝状真菌)和10种(5种细菌、1种酵母菌、4种丝状真菌)。在3个样点中,Pseudomonas baeticaVariovorax paradoxusFusarium acuminatumFusarium tricinctumPenicillium sajaroviiPenicillium griseoroseum (前2种为细菌,后4种为丝状真菌)在叶际和内生均有出现;Cladosporium subuliforme在3个样点的叶际中均有出现而内生中无;Peribacillus simplex在3个样点的内生中均有出现而叶际中无。在米拉山-内生、卡若拉-叶际、卡若拉-内生、恰拉山-内生、米拉山-叶际、恰拉山-叶际中独有菌株分别有1、5、1、3、1和2种。虽然叶际与内生独有菌株分别有14种(相对丰度共计18.00%)和10种(相对丰度共计19.71%),但这些独有菌株大部分只分布在1个或2个样点中,不同样点间的微生物组成同样存在较大差异。总体而言,垫状点地梅叶际与内生可培养微生物间的物种组成特征差异显著,主要体现在两者微生物的种群结构和各菌株相对丰度的差异上。

图 12 垫状点地梅叶际与内生可培养微生物间物种组成的多集合维恩图 Figure 12 Multi-set Venn diagram of species composition between phyllospheric and endophytic culturable microorganisms in the Androsace tapete. 黑色点表示该样独有的菌株;点线图表示样本间共有的菌株;柱状图上的数字表示样本间的共有物种数;左边柱形图表示各样本的物种数 Black dots indicate the strains unique to the sample; Dotted line graph indicates the strains shared between samples; The number on the bar graph indicates the number of species shared between samples; The left bar graph indicates the number of species in each sample.
3 讨论 3.1 垫状点地梅存活与死亡个体的叶际和内生可培养微生物的比较

垫状点地梅叶际和内生微生物物种组成比较丰富。分析叶际可培养微生物的优势属种可知,PenicilliumPenicillium sajarovii分别为优势属和优势种,而且在属水平上,优势类群的优势度比较高(相对丰度占72.00%)。垫状点地梅叶际可培养微生物偶见菌群的种类较多,有22种(相对丰度低于1.00%),这些微生物虽然丰度很低,但可能是可培养方法的局限性所致[39],事实上它们可能也与植物有着密切的联系。分析内生可培养微生物的优势属种可知,PenicilliumBacillus mycoides分别为优势属和优势种,属水平的优势类群优势度较高(相对丰度占70.80%)。垫状点地梅的内生可培养微生物偶见菌群的种类少于叶际,有14种。青霉菌属(Penicillium)是能以各种有机物质为碳源的最常见的真菌之一,广泛存在于土壤、植被、空气和各种食品等多种生境中[40-41]。垫状点地梅叶际上的凋落物及叶内糖类等有机物能为其提供良好的营养环境,培养基上也容易存活,它们还能产生多种真菌毒素,抑制其他微生物的生长[42],这可能是青霉菌能成为垫状点地梅叶际和内生微生物的优势菌属的重要原因。而蕈状芽孢杆菌(Bacillus mycoides)能产生毒性物质BmJ抑制某些真菌病原体,其分离产物已被用作植物病害防治的叶面喷雾制剂[43],推测这是其成为内生微生物优势种的原因。

通过对比垫状点地梅存活与死亡个体的叶际和内生可培养微生物,两者微生物的α多样性并无显著差异,但在物种组成上有所差别。在叶际微生物中,存活个体独有菌株有9种,优势菌群中以Penicillium sajarovii (9.71%)、Penicillium raistrickii (7.43%)和Pseudomonas baetica (6.86%)为主,包括2种细菌(13.15%)、1种酵母菌(4.57%)和7种丝状真菌(45.13%);而死亡个体独有菌株有13种,优势类群中以Penicillium sajarovii (8.57%)、Fusarium tricinctum (8.00%)和Fusarium acuminatum (7.43%)为主,包括2种细菌(10.29%)、3种酵母菌(14.86%)和5种丝状真菌(32.00%)。内生可培养微生物中,存活个体独有菌株有6种,优势类群中以Bacillus mycoides (14.00%)、Pantoea agglomerans (11.00%)和Pseudomonas baetica (8.00%)为主,其中细菌5种(40.00%)、丝状真菌5种(26.00%)。死亡个体独有菌株有14种,优势类群中以Fusarium tricinctum (8.05%)、Peribacillus simplex (6.90%)和Bacillus simplex (5.17%)为主,其中细菌7种(31.62%)、丝状真菌3种(17.25%)。

组成微生物群落的各物种彼此之间存在广泛的相互作用,包括通过产生抗生素或刺激植物防御来竞争营养物或生存空间[44-45]。来源于不同生存状态个体的叶际和内生微生物,其种类和各菌株所占比例差异较大,若环境发生变化(如宿主植物死亡),原叶际微生物组的稳态被打破,群落结构也随之改变,因此,存活与死亡个体不同的生存环境造就了各异的微生物群落。例如缺失免疫相关通路的拟南芥突变体在高湿度的环境中,细菌多样性下降,叶际微生物组失衡[11]。这种改变可能是新环境中原菌群里的某些菌株竞争力发生变化或空缺出新的生态位“招募”了新的菌株定殖造成的。在死亡个体独有菌株中Cladosporium pseudocladosporioides是红树莓果实腐烂的病原体[46]Penicillium solitum能够引起藏红花球茎的腐烂[47]Alternaria chlamydosporigena能导致番茄的叶斑病[48],正常情况下垫状点地梅存活年限有上百年[49],这些致病菌可能是造成垫状点地梅非自然死亡的原因之一。当然垫状点地梅存活与死亡个体的叶际和叶内可培养微生物的物种组成差异,可能是垫状点地梅死亡后营养条件等因素发生改变所造成的。若要明确垫状点地梅的死亡具体是由哪种菌株造成,还需进行侵染实验。

虽然垫状点地梅存活与死亡个体的叶际和叶内可培养微生物的物种组成上存在差异,并且各菌株所占比例不同,但二者群落中物种的相似度很高。在叶际可培养微生物中,共有菌株的相对丰度之和分别占存活与死亡个体的89.73%和81.15%。在内生可培养微生物中,共有菌株的相对丰度之和分别占存活与死亡个体的90.00%和70.71%。表明叶际或内生可培养微生物异养方式大多并不固定,在垫状点地梅的存活和死亡个体中均能存活,即这些共有的微生物可以兼共生和腐生生存。

3.2 垫状点地梅叶际与内生可培养微生物的比较

叶际可培养微生物较内生可培养微生物多样性更高,这与Agler等的研究结果“与内生微生物群相比,叶际微生物群似乎更加多样和丰富”一致[50]。比较垫状点地梅叶际与内生可培养微生物的多样性和物种组成,发现二者的各项α多样性指数都比较高,大多无显著差异,但在物种组成上存在显著的空间异质性。二者的优势属均为青霉属(Penicillium),独有菌株分别有14种和10种,叶际微生物的优势类群中以Penicillium sajarovii (9.14%)、Fusarium tricinctum (7.43%)、Fusarium acuminatum (6.29%)等菌株为主,而内生微生物的优势类群中以Bacillus mycoides (7.30%)、Fusarium tricinctum (6.93%)和Pantoea agglomerans (6.93%)为主。此外,聚类热图(图 9)的分析结果显示,内生微生物在同一居群的物种组成更加相似,而叶际微生物则无此现象,相较于能直接与外部环境接触、来源更广泛的叶际微生物,内生微生物所处的环境更加稳定,同一居群的叶内环境更为相似,而微生物群落对环境有选择偏好[51],同一居群的叶际环境差异更大可能是造成这一结果的主要因素。

有研究表明,植物叶表面通过气孔释放的水分可以被一层非常薄的层流层隔离,从而减轻叶际微生物所面临的水分胁迫[52];大多数植物叶片表面在显微范围内有许多褶皱,这些褶皱的低洼区域影响水滴扩散为叶际微生物提供生存空间[53];叶表面能分泌少量的葡萄糖、果糖和蔗糖等营养物质,这为叶际微生物提供了相对充足的碳源[52, 54]。相较于叶际,叶内有着更丰富而稳定的营养和水分条件[55],但内生微生物的定殖也需面临来自植物免疫的压力[56]。可能是这些独有菌株更适宜生存在叶际或叶内提供的独特微环境中,这种生存环境上的差别造成了这部分菌株的空间异质性。此外,叶际和内生可培养微生物中,共有菌株35种,相对丰度之和分别占82.00%和80.29%。其他一些研究也表明,在植物叶和根的微生物群中,尽管整体上二者的群落结构和组成有所不同,但在关键群落成员中可以大量重叠[57-59]。这表明所谓的叶际、根际和内生微生物,只是对其生存部位不同而区别定义,实际上它们大多生态位并不固定,生存空间没有确定的界限。

3.3 垫状点地梅与其他植物叶际和内生可培养微生物的比较

比较垫状点地梅与其他植物叶际或内生可培养微生物,结果如表 4所示。从垫状点地梅分离出的叶际和内生可培养微生物的属种数均较高,这可能与本文研究的微生物种类及使用的培养基较多有关。大多植物的叶际和内生可培养微生物优势属均为芽孢杆菌属(Bacillus),本文的优势属是青霉菌属(Penicillium),但在细菌类群中Bacillus同样占有优势。国内外有关叶际可培养微生物的研究较少,叶际和内生可培养微生物的研究对象大多集中在农作物和药用植物上,而且研究的菌株主要以细菌或其他功能菌株为主,对得到菌株的功能应用方面取得了许多成果。关于高原植物的叶际和内生可培养微生物的研究和应用还较为缺乏,这些在极端环境下与植物共生的微生物有着巨大的开发潜力,仍需进一步探索。

表 4 垫状点地梅与其他植物的叶际或内生可培养微生物的比较 Table 4 Comparison of phyllospheric or endophytic culturable microorganisms of Androsace tapete and other plants
The plants studied Part Species of strain Dominant
genera
Dominant species Number of genus and species
Androsace tapete Phyllosphere Bacteria and fungi Penicillium Penicillium sajarovii 22 genus, 49 species
Maize[60] Phyllosphere Nitrogen-fixing bacteria Bacillus Bacillus pumilus 16 genus, 24 species
Banana[61] Phyllosphere Antagonistic bacteria Bacillus Bacillus subtilis
Mycosphaerella fijiensis
Rape[62] Phyllosphere Bacteria Bacillus
Androsace tapete Intrafoliar Bacteria and fungi Penicillium Bacillus mycoides 19 genus, 45 species
Medicinal plants[63] Intrafoliar Bacteria and fungi Bacillus
Kobreasia capillifolia[64] Intra-root, intra-stem, intra-flower Bacteria Bacillus 11 genus,
43 species
Cannabis sativa L.[65] Intrafoliar, intra-petiole, intra-seed Bacteria and fungi Pseudomonas
Aureobasidium
Bacteria 18 genus,
fungus 13 genus
Oryza sativa[66] intra-seed Bacteria Bacillus Bacillus subtilis
Leontopodium nanum[67] Intra-root, intra-stem, intrafoliar, intra-seed Bacteria Pseudomonas
Bacillus
18 genus,
52 species
−:无数据
−: No data.
4 结论

垫状点地梅叶际和内生可培养微生物的物种组成均较为丰富。在叶际微生物中,有细菌10属18种、酵母菌5属8种、丝状真菌7属23种,其中PenicilliumPenicillium sajarovii分别为优势属和优势种。在内生微生物中,有细菌9属18种、酵母菌4属7种、丝状真菌6属20种,PenicilliumBacillus mycoides分别为优势属和优势种。

垫状点地梅存活与死亡个体的叶际和内生可培养微生物α多样性并无显著差异,在物种组成上,二者各菌株所占比例差异较大,但各群落中物种的相似度很高,表明这些共有微生物的异养方式并不固定,可以兼共生和腐生生存。在死亡个体独有菌株中,Cladosporium pseudocladosporioidesPenicillium solitumAlternaria chlamydosporigena已被证实为植物的病原体。

垫状点地梅叶际与内生可培养微生物在α多样性指数上大多无显著差异,但在物种组成上,二者存在显著的空间异质性。此外二者共有菌株的比例较高。表明二者中大多微生物的生态位并不固定,生存空间没有明确的界限。

与其他植物的叶际或内生可培养微生物相比,垫状点地梅叶际和内生可培养微生物的多样性较高,优势属与大多植物的叶际或内生可培养微生物优势属存在差异,但在本文的细菌类群中,Bacillus同样占有优势。

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