For each sample, we amplified the V4 region 16S rRNA genes
using a broadly conserved primer set (515F/806R, 50-GTGCCAGC
MGCCGCGGTAA-30/50-GGACTACHVGGGTWTCTAAT-30). The PCR
primers were constructed as follow: forward primer = 454
Titanium Lib-l Primer A/5-base barcode/forward 16S primer and
reverse primer = 454 Titanium Lib-l Primer B/reverse 16S primer
(Peiffer et al., 2013). PCR reactions were carried out in triplicate
20-lL reactions with 0.4 lM forward and reverse primers, 1-lL
template DNA, 250 nM dNTP and a 1 FastPfu buffer. All dilutions
were carried out using certified DNA-free PCR water. Thermal
cycling consisted of initial denaturation at 95 C for 2 min followed
by 25 cycles of denaturation at 95 C for 30 s, annealing at 55 C for
30 s, an extension at 72 C for 30 s, with a final extension of 5 min
at 72 C. Replicate amplicons were pooled and visualized on 2.0%
agarose gels using a SYBR Safe DNA gel stain in 1 TAE.
After purification using a spin column (QIAGEN, Düsseldorf,
Germany), DNA fragments with ligated adapter molecules on both