莫克兰冷泉区沉积物原核微生物群落组成及其环境响应

Prokaryotic community composition in Makran cold seep sediments and the response to environment

摘要:

【目的】冷泉系统广泛存在于大陆边缘地区,其典型特征是在海底渗漏出大量富含以甲烷为主的碳氢化合物和硫化氢等成分的低温流体。冷泉也因其独特的地球化学条件孕育着独特的原核微生物群落结构,然而,原核微生物组成与冷泉环境之间的响应关系却并不清楚。【方法】本文以莫克兰大陆边缘活跃冷泉区沉积物柱状样为研究对象,沿深度剖面分析了沉积物中的CH₄以及孔隙水SO₄^2-、H₂S浓度等关键地球化学参数,并基于16S rRNA基因高通量测序对冷泉沉积物原核微生物的群落结构及其空间变化进行了系统分析。【结果】根据其硫酸盐-甲烷浓度剖面特征,从上向下,将沉积物垂向剖面划分为硫酸盐还原区(SZ)、硫酸盐-甲烷转换区(SMTZ)和产甲烷区(MZ)。通过原核微生物α多样性与基因定量研究发现,随着深度增加微生物多样性与丰度呈逐渐降低的趋势。16S rRNA基因高通量测序结果表明,SZ中以硫氧化细菌γ-变形菌纲、α-变形菌纲和埃普西隆杆菌门为主,且以硫酸盐为电子受体的与有机质降解相关的原核微生物JS1、绿弯菌门、洛基古菌纲、深古菌纲及底栖古菌纲的相对含量也较高;SMTZ存在较高含量的ANME-1a、ANME-1b与SEEP-SRB1,它们耦合介导着硫酸盐还原和甲烷厌氧氧化(SR-AOM)过程。此外,深古菌纲及绿弯菌门的普遍存在说明,除甲烷外,沉积物中还可能存在其他烃类化合物。【结论】通过对莫克兰大陆边缘冷泉渗漏区沉积物中原核微生物群落结构的研究,发现细菌和古菌群落组成与冷泉系统独特的地球化学环境具有密切的联系。

Abstract:

[Objective] Cold seeps are mainly found along continental margins, which are characterized by the seepage of cold fluids rich in hydrocarbons dominated by methane and hydrogen sulfide. With unique geochemical environment, cold seep boasts unique prokaryotic community structure. However, the relationship between prokaryotic composition and cold seep environment is not clear. [Methods] In this paper, the key geochemical parameters, such as CH₄ in sediments and SO₄^2- and H₂S concentration in pore water, were measured along the depth profile based on the sediment samples from the active cold seep area of Makran continental margin. Through high-throughput sequencing of 16S rRNA gene, the community structure and spatial variation of prokaryotic microorganisms in cold seep sediments were systematically analyzed. [Results] Based on the methane- sulfate concentration, the sediments in the active seepage area of the Makran continental margin were divided into sulfate- reduction zone (SZ), sulfate- methane transition zone (SMTZ), and methanogenesis zone (MZ). It was found that the diversity and abundance of prokaryotic microorganisms decreased with the increase of depth through α diversity analysis and genetic quantification. According to the result of 16S rRNA gene sequencing, Gammaproteobacteria, Alphaproteobacteria, and Epsilonbacteraeota were the dominant prokaryotes in SZ, and the relative abundance of JS1, Chroloflexi, Lokiarchaeia, Bathyarchaeia, and Thermoprofundales which were related to organic matter degradation and used sulfate as electron donor was also high. ANME-1a, ANME-1b, and SEEP-SRB1 accounted for a large proportion in SMTZ, indicating that they might jointly mediate the anaerobic oxidation of methane coupled to sulphate reduction (SR-AOM). In addition, the prevalence of Bathyarchaeia and Chroloflexi indicated the potential of other hydrocarbons besides methane in the sediments. [Conclusion] Through the exploration of the prokaryotic communities in Makran cold seep, it is found that the bacterial and archaeal community compositions are closely related to the unique geochemical environment of the cold seep.