All libraries were independently prepared from separately cultured samples in duplicate, according to previously described protocols51 (link)–53 (link). Size selection was performed by extracting 200–400 bp DNA fragments on a 2% agarose E-gel (Invitrogen) before PCR amplification, then extracted using RNeasy MinElute cleanup kits (Qiagen). PCR amplification was performed using ≤ 14 cycles, and the resulting DNA quantified by Qubit fluorometric quantitation. Sequencing was performed using single-end reads on the Illumina HiSeq2000 sequencer.