The Transposition of Insertion Sequences in Sigma-Factor- and LysR-Deficient Mutants of Deinococcus geothermalis .

Some insertion sequence (IS) elements were actively transposed using oxidative stress conditions, including gamma irradiation and hydrogen peroxide treatment, in Deinococcus geothermalis , a radiation-resistant bacterium. D. geothermalis wild-type (WT), sigma factor gene-disrupted (∆ dgeo _0606), and LysR gene-disrupted (∆ dgeo _1692) mutants were examined for IS induction that resulted in non-pigmented colonies after gamma irradiation (5 kGy) exposure. The loss of pigmentation occurred because dgeo _0524, which encodes a phytoene desaturase in the carotenoid pathway, was disrupted by the transposition of IS elements. The types and loci of the IS elements were identified as IS Dge2 and IS Dge6 in the ∆ dgeo _0606 mutant and IS Dge5 and IS Dge7 in the ∆ dgeo _1692 mutant, but were not identified in the WT strain. Furthermore, 80 and 100 mM H 2 O 2 treatments induced different transpositions of IS elements in ∆ dgeo _0606 (IS Dge5 , IS Dge6 , and IS Dge7 ) and WT (IS Dge6 ). However, no IS transposition was observed in the ∆ dgeo _1692 mutant. The complementary strain of the ∆ dgeo _0606 mutation showed recovery effects in the viability assay; however, the growth-delayed curve did not return because the neighboring gene dgeo _0607 was overexpressed, probably acting as an anti-sigma factor. The expression levels of certain transposases, recognized as pivotal contributors to IS transposition, did not precisely correlate with active transposition in varying oxidation environments. Nevertheless, these findings suggest that specific IS elements integrated into dgeo _0524 in a target-gene-deficient and oxidation-source-dependent manner.