rumAB genes from SXT/R391 ICEs confer UV-induced mutability to Proteus mirabilis hosts and improve conjugation after UV irradiation.

Proteus mirabilis is one of the Enterobacteriales species that has been deemed as non-mutable by DNA damaging agents. A genomic analysis of P. mirabilis genomes shows that this species often does not carry pol V-encoding genes in its chromosome, which are responsible for SOS mutagenesis in other bacteria. On the other hand, the highly active umuDC homologs rumAB are carried in the mobile integrative conjugative elements (ICEs) from the SXT/R391 family that are frequently found in this species. Here we show that isolates devoid of SXT/R391 are indeed weakly or non-mutable by UV-light exposure, in contrast to isolates carrying SXT/R391 elements, some of which are mutable under these conditions. SXT/R391-bearing isolates display a variable behavior regarding UV-induced mutagenesis, despite the functionality of rumAB homologs carried by them. We also show that the globally dispersed ICEPmiJpn1 confers UV mutability to otherwise non-mutable isolates and demonstrate that this phenomenon is dependent on rumAB genes. Finally, we investigated whether rumAB genes could play a role in the conjugation of ICEPmiJpn1 and found that these genes improve the conjugation of SXT/R391 by a small margin. Taken together, these results show that the presence of rumAB in SXT/R391 ICEs endows the hosts with damage-inducible mutagenesis ability and promotes a small but significant enhancement in element transfer after exposure to UV light.