Bacterial/archaeal 16S associated with sub-bottom reef sediment

Despite being key components of biogeochemical cycling on tropical reefs, comparatively little is known about the microbial communities in deeper sediment assemblages (>1 m) below the reef benthos, especially with regards to their roles in mineralisation of organic matter and export of limiting nutrients such as nitrogen into the surrounding oligotrophic waters. Here, using 16S rRNA metabarcoding and predictive functional analysis, we present the first characterisation of microbial community structure and putative nitrogen cycling pathways in radiocarbon-dated sub-bottom sediment of up to 3.5 m beneath the reef substrate. The data suggest that sub-bottom community composition may be influenced by bioturbation, with several microbial taxa documented for the first time in this habitat that may contribute to novel ecosystem functions. The functional predictions reveal sediment microbial involvement in all major pathways of the nitrogen cycle. Coral cover was not significant in explaining the community structure of KEGG orthologs associated with microbial nitrogen metabolism, while landfill proximity significantly structured the KEGG orthologs linked to pathways which involve ammonium or nitrate as a reactant

尽管作为热带珊瑚礁生物地球化学循环的关键组成部分，学界对珊瑚礁底栖生物下方超过1米的深层沉积物组合中的微生物群落所知甚少，尤其是关于其在有机质矿化以及将氮等限制性营养盐输出至周边寡营养水域中的作用。本研究借助16S rRNA 元条形码测序（16S rRNA metabarcoding）与预测性功能分析，首次对珊瑚礁基底下方最深达3.5米的放射性碳定年礁下沉积物的微生物群落结构及潜在氮循环通路进行了表征。数据表明，礁下群落组成可能受到生物扰动的影响；本研究首次在该生境中记录到多个微生物类群，它们或可贡献全新的生态系统功能。功能预测结果显示，沉积物微生物参与了氮循环的所有主要通路。珊瑚覆盖率无法显著解释与微生物氮代谢相关的KEGG直系同源物（KEGG orthologs）的群落结构，而垃圾填埋场邻近程度则显著构建了以铵或硝酸盐为反应物的相关通路所对应的KEGG直系同源物结构。