DNA metabarcoding of the prey and microbiome of museum specimen Antarctic trematomid fishes

Study Extent

Sampling

Quality Control

Method steps

1. A large piece of stomach content (0.5 × 0.5 cm) or the entire piece of hindgut (1 cm) was placed into screwcap microtubes with 500 μl of Phosphate Buffered Saline (PBS) at pH 9. Tissue was fragmented thoroughly in each tube to ameliorate efficiency. Samples were heated to 100°C for 10 min, left to cool on ice for 5 min and then spun down with 20,000 × g for 5 min. PBS was carefully removed without taking any tissue and replaced by 500 μl of PBS at pH 7.2 and again heated to 100°C for 10 min. PBS was again carefully removed and further purification steps were conducted using the commercial Nucleospin® Tissue (Macherey-Nagel, Accession number: 740952) DNA extraction kit following the manufacturer's protocol.
2. For prey identification a 313 bp region of the COI gene was amplified from the stomach content using the tailed primers NGSmlCOIint and NGSjgHCO2198. The V3 and V4 region (460 bp) of the 16S rRNA gene was amplified using the tailed primers 16s-IllumTS-F and 16s-IllumTS-R to assess the microbiome composition. The reaction mix for the amplicon PCR for COI contained 12.5 μl of MytaqTM 2x Mix (Bioline, Accession number: BIO-25041), 0.5 μl of each primer (20 μM), 10.5 μl of molecular grade water and 1 μl of DNA template with a PCR profile of 10 s of denaturation at 95°C, 30 s of annealing at 62°C and 60 s elongation at 72°C for 16 cycles with the annealing temperature dropping every cycle by 1°C, followed by 25 cycles with an annealing temperature at 46°C. The reaction mix for the amplicon PCR for 16S contained 12.5 μl of MytaqTM 2x Mix, 2.5 μl of each primer (1 μM), 2.5 μl of DNA template (5 ng ul−1) and 5 μl of molecular grade water with a PCR profile of 60 s of initial denaturation at 95°C followed by 25 cycles of 15 s denaturation at 95°C, 15 s of annealing at 55°C and 10 s elongation at 72°C, finishing with a final extension of 72°C for 300 s. PCR products were cleaned up using Agencourt AMPure XP beads (Beckman Coulter, Accession number: A63882) following the manufacturer's instructions with a bead to template ratio of 0.8 to 1. Thereafter followed an indexing PCR, which binds a unique primer barcode to each respective sample following Lange et al. (2014) with a PCR mix of 10 μl of MytaqTM 2x Mix, 0.5 μl of each forward and reverse indexing-primer (to form a unique identifiable primer combination for each sample; 20 μM) and 9 μl of DNA template with a PCR profile of an initial denaturation of 1 min at 95°C followed by 15 cycles of denaturation for 15 s at 95°C, 15 s of annealing at 51°C and 10 s of extension at 72°C finishing with a final extension of 5 min at 72°C. The PCR product was cleaned up again, then quantified using the commercial Quant-iTTM Picogreen® kit (Thermo Fisher) and pooled, if sufficient template (20 ng) was available. Sequencing took place on an Illumina MiSeq PE 3000 (Genomics Core, KU Leuven, Belgium).

1. Trematomus eulepidotus
   rank: species
2. Trematomus penellii
   rank: species
3. Trematomus hansoni
   rank: species
4. Trematomus eulepidotus
   rank: species
5. Trematomus brachysoma
   rank: species
6. Trematomus bernacchii
   rank: species
7. Trematomus borchgrevinki
   rank: species
8. Trematomus newnesi
   rank: species
9. Trematomus loennbergii
   rank: species
10. Trematomus scotti
    rank: species

1. Bacteria
   common name: Bacteria rank: domain
2. Archaea
   common name: Archaea rank: domain

1. Eukaryota
   common name: Eukaryotes rank: domain