Fig. 1

Significant enrichment of Illumina adapter sequences in published microbial genome databases. a Histogram shows the number of assemblies in all databases containing 10 or more exact matches to the Illumina universal adapter sequence or its reverse complement. Of the 15,657 species reference genome assemblies, the number of assemblies expected to contain 10 or more exact matches by chance was ~ 1.57e-12, i.e., ~ 0. b Bar plot shows the number of assemblies displaying significant evidence of adapter enrichment at three p-value thresholds. Expected number of assemblies is shown for each threshold. c–j Histograms show the number of assemblies in individual databases for specific ranges of p-values. In (c–j), Red bars indicate the number of assemblies for which p-values were < 0.01. Dashed red lines indicate the number of assemblies expected to display p-values of < 0.01 by chance (i.e., ~ 1% of assemblies in each database)