冶炼企业周边农田土壤的多环芳烃污染及其细菌群落效应

Polycyclic Aromatic Hydrocarbons( PAHs) Pollution and Their Effects on Bacterial Community in Agricultural Soils Near a Smelting Plant

多环芳烃是一类持久性有机污染物,进入土壤后可能产生多方面生态效应。为研究多环芳烃对土壤微生物的影响,选取南京某冶炼企业周边农田样品,在分析污染物含量基础上,采用高通量测序、定量PCR等方法综合评价了土壤细菌多样性和组成以及多环芳烃降解细菌丰度等特征。17个土壤样品中,多环芳烃总量为0.25~31.08 mg·kg-1,并具有随污染源距离增加而降低的空间分布特征。与土壤理化性质如p H相比较,多环芳烃污染对土壤细菌的总体多样性和群落组成影响不显著。进一步分析发现多环芳烃与潜在降解微生物的相对丰度和降解功能基因(芳香环羟基化双加氧酶,PAH-RHDα)拷贝数显著正相关。污染较重样品的克隆、测序分析表明,土壤中PAH-RHDα基因主要属于革兰氏阳性细菌nid A3/fad A1类群,且与分支杆菌相关序列较为接近。这些结果综合评价了冶炼企业周边农田土壤多环芳烃污染对微生物群落的影响,提示土壤污染在多环芳烃潜在降解细菌中的富集作用,将为后续污染土壤生物修复提供重要科学依据。

Polycyclic aromatic hydrocarbons（PAHs） are a group of persistent organic pollutants that may pose significant risks on soil biota. In this study, 17 soil samples were collected from agricultural sites potentially polluted by a smelting plant in the outskirt of Nanjing, Jiangsu Province. The distances of the sampling sites to the potential PAHs source ranged from 500 m to 5 km. The total amounts of 15 PAHs（Σ15PAHs） in these samples ranged from0.25 ~ 31.08 mg·kg^（-1）, with most contaminated samples（ 1 mg·kg^（-1）） found in closely adjacent sites to the plant.High molecular weight PAHs（≥ 4 rings） were dominant in most samples. PAH diagnostic ratios suggested these PAHs were largely related to coal and fossil fuel combustion. To reveal the bacterial community composition, 16 S r RNA gene was amplified and analyzed using next generation sequencing. The Illumina＇s Mi Seq sequencing produced more than 225 000 reads, with averagely 13 257 reads obtained for each sample. The most abundant phyla across all samples were Proteobacteria, Bacteroidetes, Actinobacteria and Acidobacteria. Bacterial alpha diversity, as measured by observed species, Chao1, Phylogenetic Diversity（PD）, Shannon and Simpson indices, were directly correlated to p H rather than PAHs. An ordination analysis indicated that the bacterial community composition was significantly influenced by p H and total phosphorus, while the contribution of PAHs was minimal. However, the PAHs levels were positively correlated to the relative abundance of a few potential PAHs degraders such as Mycobacterium, Rhodococcus, Actinomadura and Nocardioides. This trend was further confirmed by the quantitative PCR（q PCR） quantification of bacterial PAH ring-hydroxylating dioxygenase genes（PAH-RHDα）. Although the gram negative（GN） bacterial PAH-RHDα gene abundance was below the detectable level, gram positive（GP） PAH-RHDα was recovered from all samples and its abundance was positively correlated with the PAHs pollution. The GP PAH-RHDαgene in three selected samples affiliated to the nid A3/fad A1 group, and their closest matches in Genbank were largely derived from Mycobacterium. Overall, these findings indicate the influence of industrial PAHs emission on the adjacent agricultural soils. The PAHs pollution may cause the enrichment of specific PAHs degraders such as Mycobacterium,although soil p H could be more significant in shaping total community of soil bacteria.