环境科学  2022, Vol. 43 Issue (8): 4333-4341   PDF    
基于高通量测序和代谢组学解析重金属污染对农田微生物群落组成和功能的影响
庞发虎1,2, 李晓琦2, 段莉阳2, 陈彦2, 姬明飞1, 张浩1,2, 韩辉1,2, 陈兆进1     
1. 南阳师范学院水资源与环境工程学院, 南水北调中线水源区水安全河南省协同创新中心, 河南省南水北调中线水源区流域生态安全国际联合实验室, 南阳 473061;
2. 南阳师范学院生命科学与农业工程学院, 南阳 473061
摘要: 重金属污染会影响微生物组成和群落结构,其与微生物的相互关系一直是重金属污染生态学研究的热点.河南省新乡市是中国著名的电池生产城市,因电池生产废水污灌造成严重的土壤重金属污染.目前有关新乡市长期灌溉电池废水造成的重金属污染对微生物群落组成和代谢功能的影响鲜见报道.采集了新乡市某长期生产电池厂旁3个重金属污染位点,重金属含量测定表明Cd和Pb超过相关标准,分别超标34~66倍和1.5~2.32倍.采用高通量测序分析了细菌和真菌群落组成,结果表明细菌由芽孢杆菌属、节杆菌属、鞘氨醇单胞菌属和类诺卡氏菌属等优势属,真菌由油壶菌属、小不整球壳属、Gibellulopsis和被孢霉属等优势属组成,表明经过长期的重金属胁迫,新乡长期重金属污染土壤富含重金属抗性细菌和真菌.环境因子和微生物群落相关性分析表明,总量Cu、DTPA提取态Cu和水溶态Pb显著影响细菌群落组成,总量Cd、Ni、Pb、Zn、DTPA提取态Cu和水溶态Pb显著影响真菌群落组成.目前,关于重金属污染对微生物群落代谢影响的研究较少,采用非靶向代谢组学分析表明,不同位点间代谢产物具有差异.通路富集分析表明,这些差异代谢物涉及代谢过程、环境信息处理和翻译等遗传信息加工等,在微生物缓解重金属导致的胁迫和环境适应中可能起到作用.
关键词: 新乡市      重金属污染      微生物群落和功能      高通量测序      代谢组学     
High-Throughput Sequencing Combined with Metabonomics to Analyze the Effect of Heavy Metal Contamination on Farmland Soil Microbial Community and Function
PANG Fa-hu1,2 , LI Xiao-qi2 , DUAN Li-yang2 , CHEN Yan2 , JI Ming-fei1 , ZHANG Hao1,2 , HAN Hui1,2 , CHEN Zhao-jin1     
1. International Joint Laboratory of Watershed Ecological Security and Collaborative Innovation Center of Water Security for Water Source Region of Middle Route Project of South-North Water Diversion in Henan Province, School of Water Resources and Environmental Engineering, Nanyang Normal University, Nanyang 473061, China;
2. School of Life Science and Agricultural Engineering, Nanyang Normal University, Nanyang 473061, China
Abstract: Heavy metal contamination affects microbial composition and diversity. The interaction between heavy metal contamination and soil microorganisms has been a hot topic in ecological research. Battery manufacturing has been going on for over six decades in Xinxiang City, resulting in severe soil heavy metal contamination due to battery wastewater runoff. Few studies have investigated the effect of heavy metal contamination due to long-term battery wastewater runoff on microbial diversity and metabolomics in Xinxiang City. In this study, we collected samples from three heavy metal contaminated sites in Xinxiang City and found that Cd and Pb exceeded the recommended thresholds by 34-66 fold and 1.5-2.32 fold, respectively. High-throughput sequencing showed that Bacillus, Arthrobacter, Sphingomonas, and Streptomyces were the dominant bacteria genera, while Olpidium, Plectosphaerella, and Gibellulopsis were the dominant fungi genera, indicating that heavy metal contaminated soil in Xinxiang City was rich in heavy metal tolerant bacteria and fungi due to the long-term heavy metal stress. Correlation analysis showed that total Cu, DTPA extract Cu, and water soluble Pb were significant factors in bacterial diversity, while total Cd, total Ni, total Pb, total Zn, DTPA extract Cu, and water soluble Pb were significant factors in fungal diversity. To better understand the effect of heavy metal contamination on the metabolism of soil microorganisms, we conducted non-targeted metabolomic profiling, which showed significant differences in metabolites across the samples. Pathway enrichment analysis showed that these differential metabolites were involved in pathways such as metabolism, environmental information processing, and genetic Information Processing, which may play a role in heavy metal stress mitigation and environmental adaptation.
Key words: Xinxiang City      heavy metal contamination      microbial community and function      high-throughput sequencing      non-targeted metabolomic     

土壤重金属污染已成为危害全球环境质量以及人类生存和发展的主要问题之一.由于金属冶炼、矿山开采和重金属废水灌溉等原因, 中国受重金属污染耕地面积约占全部耕地的1/5, 严重影响粮食安全[1].重金属一旦进入土壤环境中就会慢慢积累, 会影响微生物组成和群落结构等土壤生态系统.受到重金属污染的土壤, 往往富集多种耐重金属的微生物, Pacwa-Płociniczak等[2]的研究表明150 a以上污染的白玉草(Silene vulgaris)根际Cd抗性细菌数量随污染程度增加而增加.开展从微生物群落结构及多样性、均匀性方面揭示土壤功能的研究, 能深刻阐明土壤微生物对重金属胁迫的敏感程度及其变化趋势, 为改进土壤微生物修复重金属污染技术提供理论依据.目前, 高通量测序技术因其高覆盖度、高灵敏度、高准确性和低成本等特点, 在重金属污染土壤微生物群落组成、影响因素等研究中得到广泛的应用[3~6].代谢组学(metabolomics)是对生物体代谢产物进行定性定量分析的一门学科, 通过对生物体产生的代谢物进行分析可以揭示生命活动的现象和过程.微生物在重金属污染的环境中通过调节其代谢活动, 不仅使其在此环境中生存, 还可协助降低环境污染.目前, 对重金属污染土壤中群落微生物代谢物的研究开展较少[7].Wang等[8]的研究采用高通量测序结合代谢组学, 分析Cd污染土壤盐胁迫对微生物群落组成和代谢产物的影响, 结果表明盐胁迫降低土壤细菌、真菌多样性和改变其群落组成, 同时使土壤微生物代谢产物发生改变.

河南省新乡市是中国著名的轻工业城市, 被誉为“中国电池工业之都”.电池企业众多, 企业排放的电池废水造成的土壤重金属污染问题较为突出.研究者对新乡市电池废水灌溉造成的土壤和农作物重金属污染进行了研究, 其周边耕地土壤均受到不同程度的Cd、Ni、Zn和Cu等的污染, 这些区域已成为农产品安全生产的高风险区[9~12].目前有关新乡长期灌溉电池废水造成的重金属污染对土壤微生物群落组成和代谢功能影响鲜见报道[13].因此, 本文以新乡市某电池厂周边长期污染农田为研究对象, 采用高通量测序结合代谢组学的方法, 研究微生物群落组成、影响因素和代谢特征, 揭示土壤微生物对电池废水灌溉污染的响应和适应性.

1 材料与方法 1.1 样品采集和理化性质、重金属含量测定

根据文献资料, 以河南省新乡市郊区某电池厂为中心, 沿旁边河流根据距离远近, 设置3个采样点, 位点A(电池厂外河边农田土壤)、位点B(电池厂2 km外河边农田土壤)和位点C(电池厂4 km外河边农田土壤).于2019年10月采用五点采样法采集土壤, 每样品设置6个生物学重复.将收集的土壤样品置于预先灭菌容器中存于冰盒, 运回实验室用于后续高通量测序和代谢组分析, 剩余土壤样品用于理化指标测定.对收集土壤样品测定基本理化性质, 包括pH值、总氮(TN)、总磷(TP)、总钾(TK)、铵态氮(NH4+-N)和硝态氮(NO3--N)、有效磷(AP)、速效钾(AK)和有机碳(SOC), 具体步骤参考文献[14].采用欧盟DIN 38414-S4(1984)标准提取过程提取水溶性重金属, 用二乙基三胺五乙酸(diethylenetriaminepentaacetic acid, DTPA)提取土壤有效态重金属, 土壤消解液、水溶性重金属浸提液和DTPA浸提液采用电感耦合等离子体发射光谱检测土壤镉(Cd)、铜(Cu)、镍(Ni)、锌(Zn)和铅(Pb)这5种重金属元素含量.

1.2 土壤总DNA提取和高通量测序

采用FastDNA® Spin Kit for Soil试剂盒(MP Biomedicals, USA)提取土壤微生物总DNA, 采用细菌通用引物338F/806R和真菌通用引物ITS1F/ITS2R对细菌和真菌进行PCR扩增, 扩增体系参照Chen等[15], 测定浓度和纯度后送上海美吉生物医药科技有限公司进行高通量测序MiSeq PE300(Illumina Inc, San Diego, CA, USA).

1.3 高通量数据分析

将Illumina MiSeq测序得到的下机数据(Raw Data)经处理后得到Tags序列, 与数据库(Gold database)进行比对, 检测嵌合体序列, 并最终去除其中的嵌合体序列, 得到最终的有效数据(Effective Tags).采用QIIME(quantitative insights into microbial ecology)进行生物信息学分析, 根据序列的相似度, 将序列归为多个OTU(operational taxonomic unit).为了得到每个OTU对应的物种分类信息, 采用RDP classifier贝叶斯算法对97%相似水平的OTU代表序列进行分类学分析, 并在各个分类水平统计每个样品的群落组成.

1.4 代谢组分析

准确称取1 g土壤样品, 加入20 μL内标和1 mL 50%甲醇溶液, 研磨、涡旋振荡、离心取上清液, 用0.22 μm的有机相针孔过滤器过滤, -80℃下保存, 用于后续分析.非靶向代谢组分析采用Agilent 7890B Infinity气相色谱仪偶联Agilent 5977A气质联用仪进行测定, 测定条件参照文献[16].采用主成分分析(principal component analysis, PCA)来观测所有样品代谢物的聚类模式以及组内样品的重复性.采用成对的正交偏最小二乘分析(otthogonal partial least squares-discriminant analysis, OPLS-DA)来提高组间的区分程度并筛选代谢标志物, 筛选VIP值>1、P < 0.05的代谢物作为组间比较的差异代谢物.采用数据库METLIN(https://metlin scripps.edu/)和HMDB(http://www.hmdb.ca/)进行差异代谢物的鉴定.

1.5 数据处理

土壤理化性质和重金属含量、高通量测序结果等数据分析在SPSS 17.0中进行, 组间差异性检验采用t检验和单因素方差分析.

2 结果与分析 2.1 理化性质和重金属含量

表 1所示为电池厂周边污染土壤样品的特性及重金属含量测试结果, 结果表明土壤样品pH值介于8.02~8.16之间.不同位点TN、NH4+-N和NO3--N有所差异, 但未达到显著水平.位点A的TP、AP和SOC均高于位点B和C.对土壤中Cd、Cu、Ni、Pb和Zn这5种重金属含量进行了测定, ω[总量Cd, (T-Cd)]介于27.35~53.06 mg ·kg-1, ω[总量Cu, (T-Cu)]介于43.18~86.21 mg ·kg-1, ω[总量Ni, (T-Ni)]介于59.01~93.79 mg ·kg-1, ω[总量Pb, (T-Pb)]介于258.38~394.17 mg ·kg-1, ω[总量Zn, (T-Zn)]介于72.78~115.23mg ·kg-1, 重金属含量的趋势为位点A高于位点B高于位点C.参照《土壤环境质量农用地土壤污染风险管控标准(试行)》(GB 15618-2018)的规定, Cd、Cu、Ni、Pb和Zn的风险筛选值分别为0.8、100、190、170和300 mg ·kg-1.Cd和Pb超过相关标准, 分别超标34~66倍和1.5~2.32倍, 表明主要为Cd和Pb污染.对土壤DTPA提取态和水溶态重金属进行了测定, 结果如表 1所示.

表 1 土壤主要理化性质和重金属含量1) Table 1 Main chemical characteristics and heavy metal contents of soil samples

2.2 微生物群落组成

高通量测序结果表明, 位点A、B和C土壤样品细菌由40个门和946个属的细菌组成, 门水平上: 变形菌门(Proteobacteria, 占比18.72% ~23.72%, 下同)、放线菌门(Actinobacteria, 21.46% ~26.80%)、绿弯菌门(Chloroflexi, 15.03% ~22.78%)、酸杆菌门(Acidobacteria, 9.20% ~12.60%)和厚壁菌门(Firmicutes, 6.76% ~10.20%)为优势菌门; 属的水平上: 芽孢杆菌属(Bacillus)、节杆菌属(Arthrobacter)、类诺卡氏菌属(Nocardioides)、鞘氨醇单胞菌属(Sphingomonas)、盖勒氏菌属(Gaiella)和红色杆菌属(Rubrobacter)等15个优势属占全部序列的19.43% ~22.04%(图 1).真菌群落分析表明由15个门和343个属组成, 其中: 油壶菌门(Olpidiomycota)、子囊菌门(Ascomycota)和被孢菌门(Mortierellomycota)占全部序列的91.28% ~95.72%.属水平上: 油壶菌属(Olpidium)、小不整球壳属(Plectosphaerella)、Gibellulopsis属、毛壳菌属(Chaetomium)、头梗霉属(Cephaliophora)、Lophotrichus属和Paramyrothecium属等19个优势属占全部序列的51.45% ~70.42%(图 2).

图 1 属水平上细菌相对丰度分布 Fig. 1 Relative abundance of sequences at the genus level of bacterial communities

图 2 属水平上真菌相对丰度分布 Fig. 2 Relative abundance of sequences at the genus level of fungal communities

采用实时荧光定量PCR对土壤细菌和真菌丰度进行测定, 位点A、B和C土壤细菌丰度分别为1.28×109、5.73×108和4.07×108拷贝数·g-1(以土壤计, 下同), 真菌丰度分别为3.03×108、1.45×108和2.18×108拷贝数·g-1, 均呈现位点A显著高于位点B和C的趋势.

为了比较不同采样点间群落结构的差异性, 采用主坐标分析(PCoA)进行分析, 结果如图 3所示.细菌群落的PCoA分析中位点A分布于左下部、位点B分布于上部和位点C分布于右侧(图 3). 与之相似, 位点A、B和C的真菌群落通过PCoA相互分开, 分别位于左上部、右下部和右上角(图 4).采用相似性分析(analysis of similarities, ANOSIM)以及Adonis分析对数据进行组间差异分析, 结果表明位点A、B和C的细菌和真菌群落之间差异均达到极显著水平(P < 0.01).

图 3 不同样品细菌群落组成的PCoA分析 Fig. 3 PCoA results of bacterial community diversity

图 4 不同样品真菌群落组成的PCoA分析 Fig. 4 PCoA results of fungal community diversity

2.3 影响因素分析

利用Canoco 4.5软件对细菌群落与环境因子进行了RDA分析.RDA分析得到的前两个轴分别解释了总体变化的35.19%和10.29%, 总共解释了45.48%(图 5). RDA分析结果表明TK(R=0.693 2, P=0.001)、T-Cu(R=0.750 9, P=0.021)、DTPA-Cu(R=0.999 7, P=0.001)和W-Pb(R=0.946 5, P=0.006)与第1排序轴显著正相关, pH值(R=-0.877 3, P=0.023)与第1排序轴显著负相关, 这些环境因子是影响细菌群落组成的主要因素(图 5).通过斯皮尔曼相关性分析这些显著影响细菌群落组成的环境因子与细菌丰度前30的属的相关性, 结果表明DTPA-Cu和TK与细菌相关性分析结果较为相似, 与间孢囊菌属(Intrasporangium)、norank JG30-KF-CM45norank AKYG1722 均显著正相关, 与Gaiellanorank Gemmatimonadaceaenorank MB-A2-108MND1 和微枝形杆菌属(Microvirga)均显著负相关(P < 0.05).DTPA-Pb与链霉菌属(Streptomyces)、Solirubrobacternorank Microtrichales显著负相关, 与norank TK 10 显著正相关.T-Cu与小单孢菌属(Micromonospora)显著正相关, 与红色杆菌属(Rubrobacter)和norank MB- A2-108 显著负相关.

图 5 细菌群落与环境因子的RDA分析 Fig. 5 RDA analysis of bacterial communities and physicochemical characteristics of soil

真菌群落与环境因子的CCA分析如图 6所示, 前两个轴分别解释了总体变化的19.61%和11.33%, 总共解释了30.94%.CCA分析结果表明AP(R=-0.898 2, P=0.005)、T-Cd(R=-0.979 7, P=0.001)、T-Ni(R=-0.994 1, P=0.003)、T-Pb(R=-0.993 5, P=0.003)和T-Zn(R=-0.963 4, P=0.002)与第1排序轴显著负相关, DTPA-Cu(R=0.860, P=0.001)和W-Pb(R=0.999 9, P=0.021)与第1排序轴显著正相关, 这些环境因子是影响真菌群落组成的主要因素(图 6).通过斯皮尔曼相关性分析这些环境因子与真菌丰度前30的属的相关性, 结果表明DTPA-Cu和W-Pb与其他环境因子对真菌群落的影响成相反的趋势.头梗霉属(Cephaliophora)、毛壳菌属(Chaetomium)、ParamyrotheciumAlbifimbria、枝孢属(Cladosporium)和棒孢属(Corynespora)与T-Cd、T-Pb、T-Zn和T-Ni显著负相关的同时与DTPA-Cu显著正相关, 赤霉属(Gibberella)和链格孢属(Alternaria)与总量Cd、Pb、Zn、Ni显著负相关的同时与DTPA提取态Cu、W-Pb显著正相关.鐮孢菌属(Fusarium)、SolicoccozymaLophotrichus和油壶菌属与T-Cd、T-Pb、T-Zn和T-Ni显著正相关的同时与DTPA-Cu显著负相关.

图 6 真菌群落与环境因子的CCA分析 Fig. 6 CCA analysis of fungal communities and physicochemical characteristics of soil

2.4 代谢组学分析

根据模式识别模型的VIP值筛选潜在标志物, 通过分析不同样品的组成可以反映样品间的差异和距离, PCA运用方差分解, 将多组数据的差异反映在二维坐标图上, 坐标轴为能够最大程度反映方差的两个特征值.土壤阳离子和阴离子代谢物PCA得分如图 7图 8所示, 其中相同分组的点以椭圆标出, 位点A分布于右上部、位点B分布于右下部、位点C分布于左侧, 样本组之间的代谢产物具有差异.

图 7 土壤阳离子代谢物PCA分析 Fig. 7 PCA score chart of soil cation metabolites

图 8 土壤阴离子代谢物PCA分析 Fig. 8 PCA score chart of soil anion metabolites

在位点A、B和C土壤样品中共检测到7 615种代谢物, 筛选其中VIP>1和T检验P < 0.05的代谢物作为差异代谢物.结果表明位点A与位点B有245种差异代谢物, 主要为2-Methyl-5-(1-propenyl)pyrazine、7-Methoxyflavone和(S)-2-Aceto-2-hydroxybutanoic acid等.位点A与位点B相比, 代谢产物上调的有102种, 下调的有143种.位点A与位点C有285种差异代谢物, 主要为Cinncassiol D1 glucoside、Armillane、Ganoderiol I和Hydroxyhomodestruxin B等, 位点A与位点C相比, 代谢产物上调的有104种, 下调的有181种.位点B与位点C有242种差异代谢物, 主要为2-Methyl-5-(1-propenyl)pyrazine、Heliocide H3和8-Hydroxy-2-methoxy-6-methyl-1, 4-naphthoquinone等, 位点B与位点C相比, 代谢产物上调的有104种, 下调的有138种.

通路富集分析表明, 这些差异代谢物参与氨基酸代谢(amino acid metabolism)、脂质代谢(lipid metabolism)、核酸代谢(nucleotide metabolism)、次级代谢产物生物合成(biosynthesis of other secondary metabolites)和化学结构转化(chemical structure transformation maps)等代谢过程, 消化系统(digestive system)、神经系统(nervous system)和內分泌系統(endocrine system)等生物体系统(organismal systems)过程, 信号转导(signal transduction)等环境信息处理(environmental information processing), 翻译等遗传信息加工(genetic information processing)过程.位点A与位点B显著差异的代谢通路为27个, 位点A与位点C显著差异的代谢通路为26个, 位点B与位点C显著差异的代谢通路为13个(图 9).其中代谢过程的苯丙素类化合物生物合成(biosynthesis of phenylpropanoids)、植物激素生物合成(biosynthesis of plant hormones)、嘧啶代谢(pyrimidine metabolism)、阿特拉津降解(atrazine degradation)和生物体系统(organismal Systems)的矿物吸收(mineral absorption)等14个代谢通路在2组以上样品中显示差异(图 9).

图 9 不同位点间显著差异代谢通路统计 Fig. 9 Significantly differential metabolic pathways identified between samples

3 讨论

微生物对环境扰动(污染)十分敏感, 不同种类微生物对环境扰动的敏感程度不同, 因此重金属污染可能引起微生物的种类组成和丰度发生明显变化.之前很多研究已经表明长期重金属污染胁迫会改变土壤细菌群落结构组成, 重金属耐性细菌相对数量和种类增加, 成为重金属污染环境中的优势种群[2, 17].为了探究新乡长期重金属污染土壤细菌群落组成及其影响因素, 采用高通量测序的方法分析细菌群落组成, 发现优势种群为变形菌门、放线菌门和绿弯菌门等优势菌门, 芽孢杆菌属、节杆菌属和类诺卡氏菌属等为优势属(图 1), 这些优势种群也广泛存在于Li等[18]、Luo等[19]和Ren等[20]研究的重金属污染土壤中, 表明经过长期的重金属胁迫, 新乡重金属污染土壤富含重金属抗性的细菌.其中优势属芽孢杆菌属[21]、节杆菌属[22]、鞘氨醇单胞菌属[23]、链霉菌属[24]Intrasporangium[25]是已报道具有生物固定、转化和吸附等能力, 能影响土壤重金属的毒性及其迁移与释放, 提高或者降低作物对重金属积累的细菌种群, 是后续新乡重金属污染土壤生物修复的良好菌种资源.通过对位点A、B和C的细菌群落多样性指数和主坐标分析(PCoA)可以发现, 位点之间细菌群落差异显著.土壤中重金属的生物活性不仅取决于总量, 在很大程度上更加取决于重金属的形态[26~28].本实验采用DTPA和水作为浸提剂分析了土壤重金属有效形态含量, 采用RDA进一步分析影响群落的因素, 发现T-Cu与DTPA-Cu对细菌群落组成是一致的, 能显著影响细菌群落组成.同时DTPA-Cu和W-Pb对细菌群落组成影响也较为相似, 表现为RDA分析图中箭头方向一致和夹角较小(图 5).这与Sullivan等[29]研究表明的提取态重金属(Zn和Cu)是影响纽约州西部厄尔巴岛腐殖质土细菌群落组成的主要因素相一致.同时, 与其他报道类似, 环境因子(TK和pH值)也是影响新乡重金属污染土壤细菌群落的显著因素[30].

与细菌群落组成类似, 真菌优势门油壶菌门、子囊菌门和被孢菌门, 优势属油壶菌属、小不整球壳属和Gibellulopsis属等也是其他重金属污染土壤中真菌的主要组成, 表明这些种群是重金属抗性的真菌类型.其中优势属毛壳菌属[31]Neocosmospora[32]Mortierella[33]能影响重金属的生物地球化学循环, 从而影响污染土壤中植物对重金属的富集.一般认为不同类群的微生物中原核生物(细菌、放线菌)比真核生物(真菌)对重金属更敏感[34].本实验中不同位点之间真菌群落组成差异显著高于细菌, 油壶菌门和油壶菌属在不同样品中丰度也达到极显著差异, 同时真菌在PCoA分析图中位点更为分散.油壶菌门和油壶菌属是许多高等植物根部的专性寄生菌, 一般在土壤中真菌占比不是很高.Babin等[35]研究不同耕作方式和施肥强度等农业管理措施对生菜根际真菌群落差异发现, 氮肥处理组油壶菌属占比介于81.5% ~97.0%, 极显著高于对照的0.90% ~25.2%, 表明油壶菌属是生菜根际农业管理的重要指标.油壶菌属与理化性质相关性分析表明其与AP显著正相关, 位点A中占比较高可能也与该采位点之前土壤中的管理措施有关.同时总量重金属(T-Cd、T-Ni、T-Pb和T-Zn)与油壶菌属显著正相关, 有效态重金属中DTPA-Cu和W-Pb与油壶菌属显著负相关, 表明油壶菌属受到重金属形态的显著影响.真菌群落组成对重金属的响应与细菌有所差异, 总量重金属(T-Cd、T-Ni、T-Pb和T-Zn)是影响真菌的重要因素, 这与Lin等[36]的优势种群与土壤重金属显著相关的研究类似.有效态重金属中DTPA-Cu和W-Pb也能显著影响真菌群落组成, 但影响的趋势与总量重金属(T-Cd、T-Ni、T-Pb和T-Zn)相反.

利用代谢组学技术研究微生物对重金属胁迫应答过程中代谢物的变化情况, 以及从代谢水平途径上阐明微生物响应重金属胁迫的机制研究已逐渐受到广大学者的关注[37, 38]. Tian等[16]采用代谢组学分析了重金属污染土壤中小白菜根际代谢产物, 发现施用二氧化硅纳米材料虽然对小白菜生长影响较小, 但能显著增加糖和糖醇、脂肪酸和其他小分子有机酸等代谢产物, 增加的比例为1.3~66.9倍.与之类似, 本研究通过代谢组学分析表明, 不同样品之间代谢产物有明显差异, 对这些代谢产物通路富集分析表明最为主要的是代谢途径.微生物在重金属胁迫下会增加体内的代谢活动, 并分泌多种代谢物, 有助于减少重金属对微生物的毒性.差异代谢途径主要有氨基酸代谢、脂质代谢、核酸代谢等.氨基酸代谢中精氨酸和脯氨酸代谢(arginine and proline metabolism)和组氨酸代谢(histidine metabolism)在位点之间差异显著, 精氨酸和脯氨酸代谢能产生相关的渗透调节物质, 缓解Cd胁迫导致的渗透失衡[39].Pearce等[40]的研究表明, 组氨酸代谢是酵母菌Saccharomyces cerevisiae缓解Cu、Co和Ni的重要途径.重金属污染物通过多种途径在体内诱发产生大量的自由基代谢物和活性氧, 从而激发脂质过氧化, 最终导致细胞的损伤[41].膜代谢中甾体激素生物合成(steroid hormone biosynthesis)、小檗碱和蜡生物合成(cutin, suberine and wax biosynthesis)和甘油磷脂代谢(glycerophospholipid metabolism)在位点之间差异显著, 研究表明它们在缓解生物和非生物胁迫过程中起到重要作用.Kanwar等[42]的研究表明甾体激素作为一类次级代谢产物, 在缓解重金属导致的氧化胁迫起到作用.膜代谢中甾体激素生物合成是膜的成分, 因此在缓解环境胁迫导致的压力时具有功能[43].Zhang等[44]采用非靶向代谢组学分析了灵芝(Ganoderma lucidum)不同Cd胁迫条件下的代谢产物, 发现灵芝能富集甘油磷脂代谢产物, 从而缓解Cd的胁迫压力.合成的植物激素类次级代谢产物能促进植物的生长, 并增强植物对外界逆境的抗性, 根系通过分泌物分泌到土壤中[45, 46], 植物激素生物合成、植物次生代谢物生物合成在位点之间显著差异.硫代葡萄糖苷(glucosinolate)作为富含S的次级代谢产物, 在遏蓝菜(Thlaspi caerulescen)和拟南芥(Arabidopsis thaliana)缓解重金属导致的胁迫中起到作用[47, 48], 在位点A和C中差异显著.以上代谢产物可能在微生物缓解重金属导致的胁迫和环境适应中起到作用.

4 结论

(1) 新乡市某长期生产电池厂旁3个采位点重金属含量测定表明, ω(T-Cd)介于27.35~53.06 mg ·kg-1ω(T-Pb)介于258.38~394.17 mg ·kg-1, 分别超过相关标准34~66倍和1.5~2.32倍.

(2) 高通量测序结果表明, 采位点的细菌由变形菌门、放线菌门和绿弯菌门等优势菌门, 芽孢杆菌属、节杆菌属和类诺卡氏菌属等优势属组成, 真菌由油壶菌门、子囊菌门和被孢菌门等优势门, 油壶菌属、小不整球壳属和Gibellulopsis属等优势属组成.

(3) 细菌群落与环境因子进行了RDA分析表明, T-Cu、DTPA-Cu和W-Pb显著影响细菌群落组成, 真菌群落与环境因子的CCA分析表明T-Cd、T-Ni、T-Pb、T-Zn、DTPA-Cu、W-Pb显著影响真菌群落组成.

(4) 代谢组学分析样本组之间的代谢产物具有差异.通路富集分析表明: 这些差异代谢物主要包括氨基酸代谢、脂质代谢等代谢过程; 消化系统、神经系统等生物体系统过程; 信号转导等环境信息处理; 翻译等遗传信息加工过程.

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