Molecular characterization of the pA3J1 plasmid from the psychrotolerant Antarctic bacterium Pseudomonas sp. ANT_J3

The knowledge on plasmids of cold-active bacteria is highly limited. In this study, the molecular characterization of the pA3J1 plasmid of Antarctic psychrotolerant bacterium Pseudomonas sp. ANT_J3 was performed. Within this plasmid, thirteen putative open reading frames were identified. Nine of them encoded proteins involved in replication, partitioning, postsegregational elimination of plasmid-less cells (via a toxin-antitoxin system activity), multimer resolution and mobilization by conjugal transfer. These genes constitute the plasmid backbone. The functional analysis of the pA3J1 maintenance region revealed that it is a narrow host range replicon, stably maintained in the host cells by the combined activities of the partitioning and relBE-type toxin-antitoxin systems. It was also suggested that the replication system of the pA3J1 plasmid may be temperature-sensitive. Comparative analyses revealed the presence of 16 Pseudomonas plasmids encoding homologous replication proteins and 5 plasmids carrying mobA genes homologous to the corresponding gene of pA3J1. The relaxase (MobA) of the pA3J1 plasmid was classified into MOB_Q family, and the phylogenetic analysis suggested that this may be a representative of a novel group (or subgroup) within this family. The structural and comparative analyses revealed that the arrangement of genetic modules in the pA3J1 plasmid is unique.