Amplicon Sequencing Library Preparation

Primer selection, amplicon generation and purification, amplicon library construction and sequencing were performed essentially as described by Hevia et al. [17 (link)]. Briefly, the primer pair Probio_Uni / Probio_Rev [16 (link)] was used to generate amplicon pools of approximately 200 bp length. The integrity of the PCR amplicons was analyzed by electrophoresis prior to their purification using the Wizard SV Gen PCR Clean-Up System (Promega, Madison, WI), and the Agencourt AMPure XP DNA purification beads (Beckman Coulter Genomics GmbH, Bernried, Germany). Libraries for each run were diluted to 3E9 DNA molecules prior to clonal amplification. Emulsion PCR was carried out using the Ion OneTouch^™ 200 Template Kit v2 DL (Life Technologies, Guilford, CA) and sequencing of the amplicon libraries was carried out on 316 chips using the Ion Torrent PGM system and employing the Ion Sequencing 200 kit (Life Technologies). After sequencing, individual sequence reads were filtered by the PGM software to remove low quality and polyclonal sequences. Sequences matching the PGM 3’ adaptor were also automatically trimmed. All PGM quality-approved, trimmed and filtered data were exported as SFF files.