16S data from: Diversity of Pico- to Mesoplankton along the 2000 km Salinity Gradient of the Baltic Sea (Hu et al. 2016)

Study Extent

Twenty-one water samples were collected in the Kattegat, the Baltic Proper and the Gulf of Bothnia during 13th–19th of July 2013.

Sampling

Twenty-one water samples were collected in the Kattegat, the Baltic Proper and the Gulf of Bothnia using a FerryBox system installed in the ship TransPaper during 13th–19th of July 2013. The ship followed the route: Gothenburg (Sweden)—Kemi (Finland)—Oulu (Finland)—Lübeck (Germany)—Gothenburg. The FerryBox system consists of a pump with a water inlet at 3 m depth, a circuit of multiple sensors for temperature, conductivity, chlorophyll and phycocyanin fluorescence, turbidity, and oxygen as well as automated water sampling devices. A detailed description of the FerryBox system is found in Karlson et al. (in press). Manual water sampling for DNA analysis was carried out both on the Northward and Southward legs. Approximately, 10 L of seawater were collected in a polycarbonate carboy. Subsamples of 200–500 mL were filtered onto 0.22 μm pore-size mixed cellulose ester membrane filters (Merck Millipore co., Cat. No. GSWP04700) to capture plankton. The filters were frozen in liquid nitrogen on board and kept at −20 to −80°C until DNA extraction. Genomic DNA was extracted using the PowerWater® DNA isolation kit (MO-BIO Laboratories Inc, Carlsbad CA, USA) following the instructions provided by the manufacturer. The V3-V4 regions of bacterial 16S rRNA genes were PCR amplified with primers 341F (CCTACGGGNGGCWGCAG) and 805R (GACTACHVGGGTATCTAATCC) (Herlemann et al., 2011). A two step PCR procedure was applied (Hugerth et al., 2014a), with 35 (25 + 10) PCR cycles. Between the first and second PCR, and prior to pooling libraries, amplicons were purified with 8.8% PEG 6000 (Polyethylene Glycol 6000) (Merck Millipore co., Cat. No. 528877-1KG) precipitation buffer and CA beads (carboxylic acid-coated superparamagnetic beads) (Dynabeads® MyOne™ Carboxylic Acid, Cat. No. 65012; Lundin et al., 2010). Agilent 2100 Bioanalyzer (Agilent, Technologies, DNA 1000 LabChip kit) and Qubit® 2.0 Fluorometer (Invitrogen, Qubit-IT™ dsDNA HS Assay kit) were used for checking the amplicon fragment sizes and quantification. Equimolar amounts of indexed samples were mixed and sequenced with Illumina MiSeq (Illumina Inc, USA) at NGI/Scilifelab Stockholm. The sequencing reads have been submitted to the European Nucleotide Archive (ENA) under accession numbers PRJEB12362. Sequence processing was not conducted as in the journal publication, but by using the https://nf-co.re/ampliseq pipeline in which the denoising (ASV reconstruction) step was conducted with DADA2.

Method steps

1. See Sampling Description.

Water samples from a transect from Kattegatt to the Gulf of Bothnia