Raw whole Drosophila genome sequence traces have contaminant sequences from bacterial symbionts

Many Drosophila genomes have been sequenced and assembled recently, and many more genome sequencing projects are in progress. However, Drosophila have bacterial, fungal, and protozoan symbionts, and the DNA of these symbionts may be isolated in the process of sequencing Drosophila genomes. Here, we assess how much sequence is isolated from these symbionts and if the sequence contamination affected how these Drosophila genomes were assembled. We do find raw sequence from bacterial symbionts and humans in Drosophila genome sequence traces analyzed. Surprisingly, the four most-common contaminant species were shared among the Drosophila genomes. However, we do not find evidence of bacterial sequences in two published Drosophila genome assemblies.