To determine whether Submariner_Ps1 proliferation occurred within the P. salinus genome, or whether the multiple Submariner_Ps1 insertions resulted from independent introductions from a different genome (e.g. a viral host), we used 100 bp of immediately flanking sequence from all 30 Submariner_Ps1 insertions to query both amoeba and pandoravirus genomes using BLASTn.