Iron is an important influence of volcanic ash input on the evolution of deep-sea ecosystems

Volcanoes are an important link between the internal system and the surface system of the Earth, which originates from magmatic activities in the deep part of the Earth, that is, through the eruption of volcanoes to directly affect various circles in the surface layer of the Earth. As an important product of volcanic eruption, volcanic ash has a very wide range of influence, and therefore has always been a hot spot and frontier field of research in earth science. However, due to the difficulty of sampling and the lack of cross-disciplinary research, little is known about how volcanic ash inputs affect the deep-sea environment. Here, we systematically, and with a combination of geological and microbiological expertise, initiated a study of volcanic ash-affected sediments in the Kermadec Trench. It was found that in sediments also under the influence of rhyolitic volcanic ash, iron was the main factor influencing the differences in microbial communities in these deep-sea sediments. The mental test further revealed that four categories of iron functional genes significantly influenced the corresponding microbial community structure in these volcanic ash-affected sediments, namely iron acquisition-heme transport, iron acquisition-iron transport, iron acquisition-siderophore transport, and iron storage. We also mined a large number of high-quality mags from these deep-sea sediment metagenomic data, and genomic analyses revealed the presence of iron-related functional genes in the genomes of all these mags. Studies of viruses in these sediments revealed that viruses do not affect abyssal prokaryote-mediated iron cycling by directly carrying iron-related auxiliary genes, but rather regulate it by lysing associated prokaryotes involved in iron cycling. Our results provide important data and insights for a deeper understanding of microbial-mediated abyssal Fe cycling under the influence of volcanic ash.

火山是地球内部系统与地表系统之间的关键纽带，其形成源于地球深部的岩浆活动，即通过火山喷发直接作用于地球表层各圈层。作为火山喷发的重要产物，火山灰影响范围极广，长期以来都是地球科学研究的热点与前沿领域。然而由于采样难度较大且跨学科研究匮乏，学界对火山灰输入如何影响深海环境的认知仍较为有限。
本研究整合地质学与微生物学专业知识，针对克马德克海沟（Kermadec Trench）受火山灰影响的沉积物开展了系统研究。研究发现，在受流纹岩质火山灰影响的沉积物中，铁是调控该类深海沉积物微生物群落组成差异的核心驱动因子。宏转录组分析进一步揭示，四类铁功能基因显著调控了该类受火山灰影响沉积物中的微生物群落结构，具体包括铁获取-血红素转运、铁获取-铁转运、铁获取-铁载体（siderophore）转运以及铁储存四大类。
本研究还从这些深海沉积物的宏基因组数据中重构得到大量高质量病毒宏基因组组装基因组（Metagenome-Assembled Genomes，简称MAGs），基因组分析显示，所有上述MAGs的基因组中均携带铁相关功能基因。对该沉积物中病毒的研究表明，病毒并非通过直接携带铁相关辅助基因来影响深海原核生物介导的铁循环，而是通过裂解参与铁循环的相关原核生物实现调控作用。
本研究结果为深入理解火山灰影响下微生物介导的深海铁循环提供了关键数据与全新视角。