4种蚯蚓肠道微生物对砷毒性的响应差异研究

Comparative study on the responses of gut microbiota of four species of earthworms to arsenic toxicity

蚯蚓肠道是微生物多样性的一个潜在存储库。砷对蚯蚓肠道微生物群落的影响已被证实,但砷在不同蚯蚓肠道菌群中生物转化的差异仍不清楚。为了进一步阐述土壤中广泛存在的低浓度砷(浓度为5,15,25 mg/kg)对不同种类蚯蚓肠道微生物影响的差异,将4种典型蚯蚓暴露于砷污染土壤后,测定其肠道微生物组成变化,并分析砷对不同蚯蚓肠道内砷富集、形态和砷生物转化基因的影响。结果显示,所有蚯蚓组织内均存在明显的砷富集,其富集系数由高到低依次为:安德爱胜蚓(1.93)>加州腔蚓(0.80)>通俗腔蚓(0.78)>湖北远盲蚓(0.52),蚯蚓组织和肠道内砷形态主要以无机砷为主,其中As(Ⅲ)含量比例>80%,部分蚯蚓组织内还发现少量有机砷。4种蚯蚓肠道微生物群落在门水平上主要以变形菌、厚壁菌和放线菌为主,并与周围土壤细菌群落组成存在显著差异。同时,在土壤和肠道内共检测到17个砷转化基因,其中蚯蚓肠道内As(V)还原和砷转运相关基因相对丰度较高,而砷(去)甲基化基因丰度较低。此外,低浓度砷污染对蚯蚓生长无显著影响,却能引起蚯蚓肠道微生物群落的紊乱。蚯蚓种类和砷污染是引起蚯蚓肠道微生物群落组成变化的主要因素。综上,蚯蚓肠道是一个微生物介导的砷生物转化的重要热区,本研究拓展了我们对土壤动物肠道内砷生物地球化学行为的认知。

Earthworm guts are thought as a potential reservoir of microbial diversity.Low concentrations of arsenic are widespread in soil and the effect of arsenic contaminant on earthworm gut microbiota has been confirmed.However,shifts of arsenic biotransformation in different earthworm gut are largely unknown.In this study,four species of earthworms were exposed to arsenic⁃contaminated soils to explore the difference and universality of the effects of low concentrations of arsenic(i.e.,concentrations of 5,15,and 25 mg/kg)on the gut microbiota characteristics using Illumina high⁃throughput sequencing,and to examine the relationships between arsenic enrichments,arsenic species and arsenic biotransformation genes in different earthworm gut.Our results demonstrated that significant arsenic bioaccumulations in all earthworm body tissues were observed.Eisenia Andrei had the highest arsenic bioaccumulation,in which the bioconcentration factor of arsenic was 1.93,followed by Metaphire californica(0.80),Metaphire vulgaris(0.78),and Amynthas hupeiensis(0.52).Inorganic arsenic(As(V)and As(III))was predominant in earthworm body tissues and guts,where the percentage of As(Ⅲ)was more than 80%.A few of organic arsenic was also observed in E.Andrei and A.hupeiensis body tissues.Gut microbial communities in four species of earthworms were dominated by Proteobacteria(22.7%),Firmicutes(25.9%),and Actinobacteria(28.0%)at the phylum level,and were significantly different from those in the surrounding soil.In addition,a total of 17 ABGs were quantified in soil and earthworm gut samples by high throughput quantitative polymerase chain reaction(HT⁃qPCR),a higher relative abundance of genes involved in As(V)reduction and arsenic transport,and a lower abundance of genes involved in arsenic methylation and demethylation were observed in all earthworm gut samples.The earthworm gut can be a reservoir of microbes with the capability of reducing As(V)and extruding As(Ⅲ),but with little methylation and demethylation of arsenic,suggesting that ABGs played important roles in the biotransformation and bioaccumulation of arsenic.Moreover,low concentrations of arsenic did not significantly alter the survival and growth of earthworms,but it could disturb the bacterial community of earthworm gut.Changes of microbial community in the earthworm gut were mainly influenced by earthworm species and arsenic contamination.In short,this study suggested that earthworm gut was an important hotspot for the microbe⁃mediated arsenic biotransformation,and the findings of this study could broaden our understanding of the biogeochemical behavior of arsenic in the gut of soil animals.