Replication of plasmids without Ori into Thermococcus barophilus suggest utilization of recombination-dependent replication

The mechanisms underpinning replication of genomic DNA in Archaea has recently been challenged. Species belonging to two different taxonomic orders grow well in the absence of an origin of replication. Recombination-dependent replication was proposed to proceed DNA replication, but this remains to be demonstrated. Here, we pursue the investigation of the particular way some archaea manage their DNA replication with the model organism Thermococcus barophilus. In contrast to H. volcanii and T. kodakarensis, T. barophilus uses Ori-dependent replication during stationary phase. Despite this, Ori and Cdc6 could be removed, causing only slight growth retardation. Surprisingly, Ori sequences could be used to generate autonomously replicative plasmids in the absence of Cdc6. We found that any chromosomal sequence >500bp facilitates plasmid replication but only if an identical sequence is present on both plasmid and chromosome. Combining these results, we propose a new model for replication of plasmid and chromosomal DNA in Thermococcales.