Exploring the benthic eukaryotic diversity at a deep-sea hydrothermal vent (Onnuri Vent Field) in the Indian Ocean based on Illumina sequencing

Abstract

The submarine hydrothermal vent is globally distributed on the seafloor in a deep-sea area where commonly produces hot springs. The deep hydrothermal vent communities on the seafloor have been adapted to extreme conditions and may represent a unique biota. However, the deep-sea hydrothermal eukaryote community remains poorly understood. Here, we investigate the eukaryotic community in sediments nearby the Indian Ocean hydrothermal vent known as the Onnuri Vent Field (OVF) using Illumina high-throughput sequencing. Seven subsamples are collected from sediments at >2000 m in depth using the three different sampling tools (TV Grab, Multiple Corers, and Box Corer). Compared with other methods, Multiple Corers appear to be a reliable method because the uncontaminated subsample can be collected. In total, 223 operational taxonomic units (OTUs) and 387 OTUs are detected using the V4 and V9 primer sets, respectively, at station MC1906 (2019 m in depth) nearby the hydrothermal vent. Interestingly, the most abundant sequence reads in both the V4 and V9 regions of 18S rDNA amplicons are the supergroup ‘Opisthokonta’ (V4: 93%, V9: 62%), and followed by the supergroups ‘Rhizaria’ and ‘Alveolata’. However, the most abundant OTUs from the V4 and V9 primer sets belong to the supergroup ‘Alveolata’ including ciliates, apicomplexans, and dinoflagellates, but the sequence reads of the Alveolata are relatively low. These patterns of eukaryotes nearby the OVF are substantially different from those in another hydrothermal vent region (station MC1914, 4299 m in depth). In the present study, Opisthokonta is the most abundant supergroup in the OVF. Furthermore, protists are a highly diverse group and may play a critical role in the grazing food web of the OVF.