Cupriavidus metallidurans MSR33

Cupriavidus metallidurans is a major model organism for bacterial tolerance to heavy metals [Janssen et al., 2010. PloS One 5(5):e10433]. Its type strain CH34 contains at least 24 gene clusters distributed over four replicons allowing for intricate and multilayered metal responses. To gain organic mercury resistance in CH34, broad-spectrum mer genes were introduced via conjugation by the IncP-1β plasmid pTP6 [Rojas et al., 2011. PloS One 6(3):e17555]. However, we recently noted that this strain, MSR33, also showed an increased resistance to other metals (i.e., Co2+, Ni2+, and Cd2+). As we did not understood this phenomenon we decided to thoroughly investigate this matter by re-sequencing the entire genome of MSR33 and comparing the basal gene expression profiles of both strains. We identified 10 indels and 9 SNPs while detecting 107 differentially expressed genes. Sequence data irrevocably implicated the transposition of IS1088 in higher Co2+ and Ni2+ resistances and altered gene expression, although the precise mechanisms of the augmented Cd2+ resistance in MSR33 remain elusive. Clearly, conjugation procedures involving large complex genomes and extensive mobilomes pose a considerable risk towards the introduction of unwanted, undocumented genetic changes. Special efforts are needed for the applied use and further development of small non-conjugative broad-host plasmid vectors, ideally involving CRISPR-related and advanced biosynthetic technologies.