Temperature incubations of microbial communities from two different locations in Fram Strait

This dataset includes 18S and 16S metabarcoding data from two temperature incubation experiments conducted on board the RV Polarstern, using a unicellular microbial community collected from different stations in the Fram Strait during the PS126 campaign on June 1st, 2021 (Soltwedel et al., 2021). The initial samples were obtained from a depth of 15 m using CTD-bound Niskin bottles (SBE 32 Carousel Water Sampler attached to a Seabird SBE911+ CTD system; Seabird Scientific, Bellevue, WA, USA) and, following filtration through a 150 µm mesh, the communities were incubated on plankton wheels within three temperature-controlled containers. To simulate current and potential future temperature scenarios in the Arctic Ocean, we selected a control temperature of 2°C, an intermediate warming scenario of 6°C, and a higher warming scenario of 9°C while varying several other parameters such as light, nutrients and dilution level. A volume of 500 mL of water was carefully vacuum-filtered (<200 mbar) through polycarbonate filters with a nominal pore size of 0.8 µm (Nucleopore, Whatman, Maidstone, UK). The filters were placed in 2 mL cryovials containing 650 µL of warm extraction buffer and stored at -80 °C. Following cell lysis using a MagNa Lyser (Roche Diagnostics, Basel, Switzerland), DNA extraction was carried out using the NucleoSpin Soil extraction kit (Macherey-Nagel GmbH, Düren, Germany), according to the manufacturer's protocol. DNA concentrations were measured with a NanoDrop 8000 spectrophotometer (ThermoFisher Scientific, Waltham, MA, USA) and standardized to 5 ng/µL. Amplicons were generated from the variable region 4 (V4) of the 18S rRNA gene for eukaryotes and the 16S rRNA gene for bacteria, using standard amplicon library preparation protocols (Illumina 16S Metagenomic Sequencing Library Preparation, Part #15044223 Rev. B, San Diego, CA, USA). Primers used for 18S rRNA gene sequencing were CCAGCASCYGCGGTAATTCC (forward) and ACTTTCGTTCTTGAT (reverse) following Bradley et al. (2016), while 16S rRNA gene sequencing employed GTGCCAGCMGCCGCGGTAA (forward) and GGACTACHVGGGTWTCTAAT (reverse) as per Fadeev et al. (2018), all incorporating Illumina adapters. Individual samples were indexed using the Nextera XT Index Kit v2 Set A primers (Illumina, San Diego, CA, USA). The libraries were pooled for 18S and 16S rRNA gene sequencing separately and sequenced on an Illumina MiSeq platform, producing paired-end reads. Demultiplexing and FASTQ file generation were performed via the MiSeq software's Generate FASTQ workflow.