南海海滩岩微生物群落结构和特定菌株对其成因机制的启示

Microbial communities and specific strains within beachrocks of the South China Sea:implications for the origin of beachrock

热带—亚热带潮间带沉积物中丰富的菌—藻类微生物及其复杂的生命活动对颗粒的早期胶结过程起重要作用。本文通过16S r RNA高通量基因测序方法分析西沙群岛石屿、全富岛及海南龙湾珊瑚礁滨岸带海滩岩表生微生物群落结构,确定主导海滩岩快速胶结的共性菌株/微生物功能群。表层生长草皮海藻的全富岛海滩岩原核生物多样性最高。龙湾潮间带上部暴露时间较长的海滩岩比潮间带下部海滩岩原核生物多样性高。相对固结的石屿海滩岩原核生物多样性最低。4个取样点具有较为相似的细菌门类组成,物种丰度由大到小依次为变形菌门(Proteobacteria)、拟杆菌门(Bacteroidetes)、放线菌门(Actinobacteriota)、蓝细菌门(Cyanobacteria)、绿弯菌门(Chloroflexi)、芽单胞菌门(Gemmatimonadota)和脱硫杆菌门(Desulfobacterota)。不同点位的海滩岩形成环境中蓝细菌主要种类大体相同,其中眉藻(Calothrixsp.)是主导海滩岩早期胶结的共性钙化菌株,通过分泌胞外聚合物成为碳酸盐矿物沉淀的“热点”。群落中检出的反硝化细菌和硫酸盐还原菌表明海滩岩内部氧化还原梯度较大,表面下极浅处即存在缺氧微环境。微生物群落内强烈的光合作用、硫酸盐还原作用和反硝化作用不断提高微环境pH值,有利碳酸盐矿物在粒间孔内的成核和生长并加速颗粒胶结。

Abundant bacterial-algal microorganisms and their metabolisms play important roles in early cementation of beachrocks along intertidal-supratidal zones of tropical-subtropical shorelands.In this study,16S rRNA high-throughput sequencing analysis was employed to reveal the compositions of prokaryotic microbial communities and identify the common strains/microbial functional groups that dominated the beachrocks’cementation.The Quanfu turf algae-bearing beachrocks have the highest biodiversity.The diversity of Longwan beachrocks in upper intertidal zone is higher than that in lower intertidal zone.The prokaryotic biodiversity of consolidated Shiyu beachrocks is the lowest.The bacterial phylum in the four sampling localities was roughly similar,which includes Proteobacteria,Bacteroideta,Actinobacteria,Cyanobacteria,Chloroflexi,Gemmatimonadetes and Desulfobacterota in descending order.The main cyanobacteria species were same.The common calcified cyanobacterial strain-Calothrix sp.was all detected,and the extracellular polymer substances could be the hotspots for precipitation of carbonate biomaterials.Denitrobacteria and sulfate-reducing bacteria detected in microbial communities indicate the anaerobic environment and steep redox gradient below the superficial beachrocks.Strong photosynthesis,sulfate reduction and denitrification in particle surface and intergranular pore together significantly rise pH,and promote the nucleation and growth of carbonate biomaterials,accelerating the consolidation of loose beach sands.