Analysis of available ascovirus, iridovirus and ichnovirus genomes provides some of the first molecular support for the hypothesis that ichnoviruses evolved from ascoviruses by symbiogenesis. However, examining genes shared only by ascovirus, iridovirus and ichnovirus genomes likely limits the sources of genes that contributed to the evolution and complexity of these viruses, especially of the role of lateral gene transfer. Relevant to this is the recent finding that an important part of the mimivirus and phycodnavirus genomes had a bacterial origin [28] . Obviously, this did not lead to the conclusion that these viruses had a bacterial origin. The cytoplasmic environment in which these viruses replicate is rich in bacterial DNA because their amobae and unicellular algae hosts feed on bacteria that they digest in their cytoplasm. Thus, it has been proposed [28] that lateral transfers of bacterial DNA within these viral genomes were driven by intimate coupling of recombination and viral genome replication. Indeed, replication of these viruses is similar to that of bacteriophage T4. This mode of replication has been called recombination-primed replication. It permits integration of DNA molecules with sequence homology as short as 12-bp [28, 40] . The replication machinery used by ascoviruses, iridoviruses, mimiviruses, phycodnaviruses, and other nucleocytoplasmic large DNA viruses (NCLDV) [41, 42] is common to all of them, despite differences in the specifics of replication in each virus family. It can therefore be expected that recombination-primed replication occurred repeatedly during evolution of both these viruses and the genome of their eukaryotic hosts. In an eukaryotic cellular environment in which bacteria, chromosomes, NCLDV viruses and non-NCLDVs (such as baculoviruses) intimately cohabit temporarily or permanently, recombination-primed replication is able to allow reciprocal passive lateral transfers between viral genomes, host chromosomes, and bacterial DNA. Under these conditions, lateral transfers are considered passive since they just result from the intimate environment and not from an active mechanism dedicated to genetic exchanges. In ascoviruses and iridoviruses, the occurrence of such lateral transfers is supported by BLASTp searches that detected the presence of ORFs whose closest relatives have their origin within eukaryotic genomes (e.g., for DpAV4, in Additional data 1, ORFs 029, 049, 077, 080, 083, 118), bacterial genomes (e.g., for DpAV4, in Additional data 1, ORFs 056, 057, 059, 112, 115 and119) or viruses belonging to other NCLDV and non-NCLDV families (e.g., for DpAV4, in Additional data 1, ORFs 007, 037, 062, 068).