Transposition of insertion sequences by dielectric barrier discharge plasma and gamma irradiation in the radiation-resistant bacterium Deinococcus geothermalis

Abstract

Insertion sequences (ISs) of the radiation-resistant bacterium Deinococcus geothermalis are transposed into other loci by oxidative stress through hydrogen peroxide treatment. Gamma irradiation and dielectric barrier discharge (DBD) plasma radiation are known to produce a variety of oxidative stress agents such as reactive oxygen species and reactive nitrogen species. Therefore, to determine whether the transposition of ISs was induced in D. geothermalis by both gamma irradiation and DBD plasma radiation, we selected non-pigmented mutants with disrupted target genes encoding carotenoid biosynthesis enzymes such as a phytoene synthase (dgeo_0523) and a phytoene desaturase (dgeo_0524). Different DNA-binding protein-deficient mutants exhibited novel transposition of ISs. Dps (dgeo_0257), OxyR (dgeo_1888), and the LysR (dgeo_2840) family regulator, in addition to cystine importer-disrupted and -overexpressed mutants (dgeo_1986–87 and dgeo_1985R) and wild-type D. geothermalis were tested in this study. Active IS transposition was not detected in two wild-type control species (Deinococcus radiodurans and Deinococcus radiopugnans) after phenotypic selection in gamma irradiation. Our finding demonstrated that gamma irradiation triggers the transposition of particular IS elements, especially ISDge2 and ISDge3 of the IS1 family, ISDge5 of the IS701 family, and ISDge6 of the IS5 family in wild-type strain and the Δdgeo_0257, Δdgeo_1986–87, Δdgeo_1985R, and Δdgeo_2840 mutants. Furthermore, DBD plasma radiation triggered the transposition of ISDge11 of the IS4 family in the wild-type strain; ISDge6 of the IS5 family on Δdgeo_0257, Δdgeo_1888 and Δdgeo_2840; ISDge5 of the IS701 family on Δdgeo_0257 strain.