Abstract
During an oxidative stress-response assay on a putative Dps-like gene-disrupted Δdgeo_0257 mutant strain of radiation-resistant bacterium Deinococcus geothermalis, a non-pigmented colony was observed among the normal reddish color colonies. This non-pigmented mutant cell subsequently displayed higher sensitivity to H2O2. While carotenoid has a role in protecting as scavenger of reactive oxygen species the reddish wild-type strain from radiation and oxidative stresses, it is hypothesized that the carotenoid biosynthesis pathway has been disrupted in the mutant D. geothermalis cell. Here, we show that, in the non-pigmented mutant cell of interest, phytoene desaturase (Dgeo_0524, crtI), a key enzyme in carotenoid biosynthesis, was interrupted by transposition of an ISDge7 family member insertion sequence (IS) element. RNA-Seq analysis between wild-type and Δdgeo_0257 mutant strains revealed that the expression level of ISDge5 family transposases, but not ISDge7 family members, were substantially up-regulated in the Δdgeo_0257 mutant strain. We revealed that the non-pigmented strain resulted from the genomic integration of ISDge7 family member IS elements, which were also highly up-regulated, particularly following oxidative stress. The transposition path for both transposases is a replicative mode. When exposed to oxidative stress in the absence of the putative DNA binding protein Dgeo_0257, a reddish D. geothermalis strain became non-pigmented. This transformation was facilitated by transposition of an ISDge7 family IS element into a gene encoding a key enzyme of carotenoid biosynthesis. Further, we present evidence of additional active transposition by the ISDge5 family IS elements, a gene that was up-regulated during the stationary phase regardless of the presence of oxidative stress.
Highlights
Genus Deinococcus is an aerobic Gram-positive bacterium capable of surviving in several extreme and/or harmful conditions [1,2,3]
Since the D. geothermalis strain contains carotenoid—a carotene known to play a role in the protection of oxidative stress—it appears likely that this mutant strain has disruptions in the carotenoid-biosynthesis pathway
We have examined the possibility that DNA-protecting protein DNA-binding protein from starved cells (Dps) controls the transposition of insertion sequence (IS) elements in genomic plasticity
Summary
Genus Deinococcus is an aerobic Gram-positive bacterium capable of surviving in several extreme and/or harmful conditions (e.g., high levels of radiation, desiccation, oxidative stress, and starvation) [1,2,3]. Since the D. geothermalis strain contains carotenoid—a carotene known to play a role in the protection of oxidative stress—it appears likely that this mutant strain has disruptions in the carotenoid-biosynthesis pathway To support this hypothesis, we report evidence that a key enzyme of carotenoid biosynthesis was disrupted due to transposition of a unique type of transposase. We report evidence that a key enzyme of carotenoid biosynthesis was disrupted due to transposition of a unique type of transposase For this reason, we have examined the possibility that DNA-protecting protein Dps controls the transposition of insertion sequence (IS) elements in genomic plasticity. IS elements are frequently identified by their unique sequence features (e.g., transposase-encoding genes, terminal inverted repeats (TIR), and direct repeats (DR)) in the target sequence generated upon insertion [14,15] These ISs are usually 750~2000 bp and encode enzymes causing transposition. We identified, for the first time in D. geothermalis, that the non-pigmented phenotypical transition due to the key enzyme of carotene biosynthesis dgeo_0524 (crtI) encoding a phytoene desaturase was inactivated by the transposition of an active IS element under oxidative stress conditions
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