Abstract
Radiation-resistant bacterium Deinococcus geothermalis has a total of 73 insertion sequences (ISs) in genomes, and some of them are actively transposed to other loci with replicative mode due to oxidative stress of hydrogen peroxide treatment. Here, we detected two transposition events in wild-type (WT) strain and LysR family member gene disrupted strain (Δdgeo_2840). Similar to our previous report (Lee et al., 2019), phytoene desaturase (dgeo_0524), a key enzyme of carotenoid biosynthesis, was disrupted by the integration of IS element, thereby detected a single phenotypically non-pigmented colony in each WT and Δdgeo_2840 strain. Two separate types of IS element have been integrated into non-pigmented clones: ISDge11 for WT and ISDge6 for Δdgeo_2840 strain. Surprisingly, Δdgeo_2840 mutant strain revealed higher resistance to oxidative stress than WT strain at late exponential growth phase. From the qRT-PCR analysis, OxyR (dgeo_1888) was highly up-regulated to 30-fold by oxidative stress through hydrogen peroxide treatment in both WT and Δdgeo_2840 mutant strains. However, the oxidative stress response enzyme, catalase or superoxide dismutase, was not significantly induced by overexpressed OxyR. Thus, a putative LysR family regulator Dgeo_2840 controlled the expression of ISDge6 type transposase and the induction of OxyR under oxidative condition. There is LysR family DNA-binding protein dependent active transposition of specific type IS and the up-regulated OxyR has not positively controlled ROS scavenger enzymes in D. geothermalis.
Highlights
Genus Deinococcus species can generally survive extreme and/or harmful conditions such as high stress of radiation, oxidative stress, desiccation, toxic substances, and starvation (Battista et al, 1999; Cox and Battista, 2005; Slade and Radman, 2011)
During the oxidative stress response assay in wild-type and dgeo_2840 mutant strain, we isolated a non-pigment colony of WT treated by continuous culture with 50 mM H2O2
The non-pigment strain of WT may be malfunctioned in the carotenoid biosynthesis gene that makes the phenotype red. dgeo_2840 strain may have a different regulatory network with more viable oxidative stress responses than WT
Summary
Genus Deinococcus species can generally survive extreme and/or harmful conditions such as high stress of radiation, oxidative stress, desiccation, toxic substances, and starvation (Battista et al, 1999; Cox and Battista, 2005; Slade and Radman, 2011). For the survival strategy of the Deinococcus strain under various stressors, Deinococcus radiodurans has been well-studied for oxidative stress responses, and appears to coordinate in multiple ways, separated into five categories as described below: (1) DNA repair systems such as RDR regulon Rec, Ssb, Uvr, and Ddr proteins; (2) high efficiency of enzymatic reactions, such as catalase, peroxidase, and superoxide dismutase; (3) unique protective deinococcal proteins, such as Irr and Ppr, and DNA protection protein in stress condition such as Dps; (4) protective small molecules: pigment compound, such as carotenoids, metal ions, such as manganese, and other antioxidant systems including redox potential control by bacillithiol. The famous transcriptional regulator OxyR of LTTR main member positively controls a number of oxidative stress response related genes in Escherichia coli, such as catalase/hydroperoxidase I (katG), a non-specific DNA-binding protein (dps), alkyl hydroperoxide reductase (ahpCF), glutathione reductase (gorA), glutaredoxin 1 (grxA), and a small regulatory RNA (oxyS). We hypothesized that IS transposition occurred in carotenoid biosynthesis pathway
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