Distribution of leech and bacterial BLASTn hits among the 13,873 contigs assembled from the 454 pyrosequencing reads.

Ambiguous hits indicate those contigs that matched both leech and bacteria simultaneously. In the 1E−5 protocol, both the leech and ambiguous hits, as well as the contigs without match were deleted from the data set. Also, 27 out of the 207 contigs matching both associates at 1E−2 (the remaining 180 hits were predicted leech hits at 1E−5) were deleted from the 2,247 contigs matching bacteria at 1E−5 resulting in 2,220 definitively bacterial hits in the data set. See the results section for further discussion.