Influence of Redox Imbalances on the Transposition of Insertion Sequences in Deinococcus geothermalis

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 ISDge2 and ISDge6 in the ∆dgeo_0606 mutant and ISDge5 and ISDge7 in the ∆dgeo_1692 mutant, but were not identified in the WT strain. Furthermore, 80 and 100 mM H2O2 treatments induced different transpositions of IS elements in ∆dgeo_0606 (ISDge5, ISDge6, and ISDge7) and WT (ISDge6). 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.

Hydrogen peroxide treatment induces the transposition of an insertion sequence in Deinococcus radiopugnans DY59

Deinococcus radiopugnans DY59 (formerly Deinococcus swuensis DY59) is a radiation-resistant bacterium isolated from soil. From the 3.5 Mb genomic DNA sequence of strain DY59 (December 2014), 31 insertion sequence (IS) elements of six IS families including IS1, IS4, IS5, IS66, IS630, and IS701 and five unclassified IS elements were detected. Upon induction of oxidative stress with 80 and 100 mM H₂O₂, the unique ISs of the IS4 family member were actively translocated into a carotenoid biosynthesis gene phytoene desaturase (QR90_10400), resulting in non-pigment phenotypic selection. Therefore, these active transpositions of a specific IS family member were induced by oxidative stress at 80 and 100 mM H₂O₂. Furthermore, D. radiopugnans DY59 exhibited extremely higher MIC values against H₂O₂ treatment. To explain this phenomenon, qRT-PCR was conducted to assess the expression levels of catalase and three LysR family regulators. Our findings indicated that the ISDrpg2 and ISDrpg3 elements of the IS4 family were actively transposed into the phytoene desaturase gene by H₂O₂ treatment via replicative transposition. However, high H₂O₂ resistance did not originate from H₂O₂-induced expression of catalase and LysR family regulators.

Adaptive Response of Thermophiles to Redox Stress and Their Role in the Process of dye Degradation From Textile Industry Wastewater

Release of dye-containing textile wastewater into the environment causes severe pollution with serious consequences on aquatic life. Bioremediation of dyes using thermophilic microorganisms has recently attracted attention over conventional treatment techniques. Thermophiles have the natural ability to survive under extreme environmental conditions, including high dye concentration, because they possess stress response adaptation and regulation mechanisms. Therefore, dye detoxification by thermophiles could offer enormous opportunities for bioremediation at elevated temperatures. In addition, the processes of degradation generate reactive oxygen species (ROS) and subject cells to oxidative stress. However, thermophiles exhibit better adaptation to resist the effects of oxidative stress. Some of the major adaptation mechanisms of thermophiles include macromolecule repair system; enzymes such as superoxide dismutase, catalase, and glutathione peroxidase; and non-enzymatic antioxidants like extracellular polymeric substance (EPSs), polyhydroxyalkanoates (PHAs), etc. In addition, different bacteria also possess enzymes that are directly involved in dye degradation such as azoreductase, laccase, and peroxidase. Therefore, through these processes, dyes are first degraded into smaller intermediate products finally releasing products that are non-toxic or of low toxicity. In this review, we discuss the sources of oxidative stress in thermophiles, the adaptive response of thermophiles to redox stress and their roles in dye removal, and the regulation and crosstalk between responses to oxidative stress.