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.

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The genome of the radiation-resistant bacterium Deinococcus geothermalis contains 19 types of insertion sequences (ISs), including 93 total transposases (Tpases) in 73 full-length ISs from the main chromosome and 2 mega plasmids. In this study, 68 ISs from the D. geothermalis genome were extracted to implicate the earlier genome before its mutation by transposition of ISs. The total size of eliminated ISs from genome was 78.85 kb. From these in silico corrections of mutation by the ISs, we have become aware of some bioinformatics factualness as follows: (1) can reassemble the disrupted genes if the exact IS region was eliminated, (2) can configure the schematic clustering of major DDE type Tpases, (3) can determine IS integration order across multiple hot spots, and (4) can compare genetic relativeness by the partial synteny analysis between D. geothermalis and Deinococcus strain S9. Recently, we found that several IS elements actively transferred to other genomic sites under hydrogen peroxide-induced oxidative stress conditions, resulting in the inactivation of functional genes. Therefore, the single species genome’s mobilome study provides significant support to define bacterial genome plasticity and molecular evolution from past and present progressive transposition events.

Pathogenic bacteria that colonize the human intestinal tract have evolved strategies to overcome acidic conditions when they pass through the gastrointestinal tract. Amino acid-mediated acid resistance systems are effective survival strategies in a stomach that is full of amino acid substrate. The amino acid antiporter, amino acid decarboxylase, and ClC chloride antiporter are all engaged in these systems, and each one plays a role in protecting against or adapting to the acidic environment. The ClC chloride antiporter, a member of the ClC channel family, eliminates negatively charged intracellular chloride ions to avoid inner membrane hyperpolarization as an electrical shunt of the acid resistance system. In this review, we will discuss the structure and function of the prokaryotic ClC chloride antiporter of amino acid-mediated acid resistance system.