Planktonic communities 16S raw sequencing reads
DNA was extracted by the standard phenolchloroform method (Wu et al., 2007) and purified using a PowerClean DNA Clean-Up Kit (Mo Bio Laboratories, Carlsbad, CA, USA). The V4 hypervariable regions of bacterial 16S rRNA genes were amplified with the primers F515 (5-GTGCC AGCMGCCGCGG-3) and R806 (3-TAATCTW TGGGVHCATCAG-5) (Li et al., 2014). For pooling multiple samples in one run of Illumina sequencing, a unique 12-mer tag for each DNA sample was added to the 5 end of both primers. Three replicates of each sample were PCR-amplified in a 25 l reaction, which contained 2.5 l 10  PCR Accuprime buffer II, 0.5 U of AccuPrime Taq DNA Polymerase High Fidelity (Invitrogen, Carlsbad, CA, USA), 0.2 M each primer, and 10 ng of genomic DNA. Cycling conditions were as follows: 94 C for 1 min followed by 25 cycles of denaturation at 94 C for 20 s, annealing at 50 C for 25 s, extension at 68 C for 45 s, and a final extension at 68 C for 10 min. The PCR products were visualized on 1% agarose gels, and the positive amplicons were quantified using the PicoGreen dsDNA Assay kit (Invitrogen), equall combined and purified with Zymos Genomic DNA Clean & Concentrator kit (Zymo Research Corporation, Irvine, CA, USA). Finally, amplicons were sequenced using the Illumina MiSeq platform.