Data Analysis
The composition of microbiota was determined by sequencing 16S rRNA genes using the 454 GS Junior Sequencer platform (Roche) according to the manufacturer’s instructions. NGS-data were automatically processed using the ‘Full Processing Amplicon’ pipeline available through the Run Wizard on the GS Junior Attendant PC (Roche). FASTA-formatted sequences were extracted from the .sff data file and processed using modules implemented in the Mothur v. 1.33.0 software platform19. Primer sequences were trimmed and sequences with length smaller than 400 were removed from the analysis. In addition, only the first 450 bases of each sequence were used for further analysis. In order to characterize the number of chimeric sequences more precisely, no additional quality filtering was applied. Unique sequences were aligned using the ‘align.seqs’ command and an adaptation of the Bacterial SILVA SEED database release 119 as a template (available at: http://www.mothur.org/wiki/ Silva_reference_alignment). Potentially chimeric sequences were detected and removed with the Uchime source code, using firstly the sequences as their own reference and sequentially the SILVA alignment version of the gold database (available at: http://www.mothur.org/wiki/ Silva_reference_alignment) as reference. The remaining aligned sequences were classified using a naïve Bayesian classifier with the SILVA SEED database release 119 and clustered into OTUs defined by 97% similarity. To reduce the effects of uneven sampling, all nose swab samples were rarefied to 500 sequences per sample and all other samples, including the synthetic community, feces, and sludge samples, were rarefied to 1000 sequences per sample. For all samples, rarefaction curves were plotted and the inverse Simpson’s diversity index and Good’s coverage were calculated. Finally, OTUs corresponding to the Streptococcus genus within the synthetic community were determined at species-level by checking the representative sequences against the reference sequences using Bionumerics version 5.10 (Applied Math).