16S/ITS rRNA of St George Island soils
We sequenced the V4 hypervariable region of the 16S rRNA using the 515-F (GTGCCAGCMGCGGTAA) and 806-R (GGACTACHVGGGTWTCTAAT) primer pair for bacteria and archaea. For fungi, we sequenced the first internal transcribed spacer (ITS1) region of the rRNA operon using the ITS1-F (CTTGGTCATTTAGAGGAAGTAA) and ITS2 (GCT-GCGTTCTTCATCGATGC) primer pair (Walters et al. 2016). We amplified marker genes using PCR (Roche LightCycler 96) with Illumina adapters and unique error-correcting 12-bp barcodes. PCR was conducted in 40 L triplicate reactions per sample, using 3 L of extracted DNA, 3 L of each primer, 20 L of MyFi PCR Mix (Bioline, Taunton, MA, USA), and 11 L of water. PCR consisted of an initial denaturing step at 95 C for 1 min, 35 cycles of amplification (95 C for 15 s, 60 C for 15 s, and 72 C for 15 s), and a final elongation step of 72 C for 3 min. Negative controls were included to detect potential contamination. Amplicon products were quantified fluorescently with ThermoFisher Scientific Quant-It PicoGreen dsDNA assay, pooled in equimolar concentration, and sequenced on an Illumina Miseq instrument at the Microbiome Core of the University of Arizona (Tucson, USA).