Fig 1. Addition of new sequences.
(A) BLAST search when new sequences are added to the database. At time t, the database is Dt. In next δt interval, new sequences Dt+δt − Dt are added, and the database becomes Dt+δt. With the traditional approach, the prior search result at time t cannot be reused, and we have to perform an entire BLAST search against the entire Dt+δt database. (B) BLAST search when several taxon-specific databases are present and a result against the combined database is needed. For three taxa, A, B, and C, we can perform individual BLAST searches against the databases DA, DB, DC, respectively. If we want to obtain a search result against the combined database DA∪B∪C, we need to merge the search results in a way that their e-values reflect the combined database size.