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The genetic platforms of Deinococcus species remain the only systems in which massive ionizing radiation (IR)-induced genome damage can be investigated in vivo at exposures commensurate with cellular survival. We report the whole genome sequence of the extremely IR-resistant rod-shaped bacterium Deinococcus ficus KS 0460 and its phenotypic characterization. Deinococcus ficus KS 0460 has been studied since 1987, first under the name Deinobacter grandis, then Deinococcus grandis. The D. ficus KS 0460 genome consists of a 4.019 Mbp sequence (69.7% GC content and 3894 predicted genes) divided into six genome partitions, five of which are confirmed to be circular. Circularity was determined manually by mate pair linkage. Approximately 76% of the predicted proteins contained identifiable Pfam domains and 72% were assigned to COGs. Of all D. ficus KS 0460 proteins, 79% and 70% had homologues in Deinococcus radiodurans ATCC BAA-816 and Deinococcus geothermalis DSM 11300, respectively. The most striking differences between D. ficus KS 0460 and D. radiodurans BAA-816 identified by the comparison of the KEGG pathways were as follows: (i) D. ficus lacks nine enzymes of purine degradation present in D. radiodurans, and (ii) D. ficus contains eight enzymes involved in nitrogen metabolism, including nitrate and nitrite reductases, that D. radiodurans lacks. Moreover, genes previously considered to be important to IR resistance are missing in D. ficus KS 0460, namely, for the Mn-transporter nramp, and proteins DdrF, DdrJ and DdrK, all of which are also missing in Deinococcus deserti. Otherwise, D. ficus KS 0460 exemplifies the Deinococcus lineage.

Despite concerted functional genomic efforts to understand the complex phenotype of ionizing radiation (IR) resistance, a genome sequence cannot predict whether a cell is IR-resistant or not. Instead, we report that absorption-display electron paramagnetic resonance (EPR) spectroscopy of nonirradiated cells is highly diagnostic of IR survival and repair efficiency of DNA double-strand breaks (DSBs) caused by exposure to gamma radiation across archaea, bacteria, and eukaryotes, including fungi and human cells. IR-resistant cells, which are efficient at DSB repair, contain a high cellular content of manganous ions (Mn2+) in high-symmetry (H) antioxidant complexes with small metabolites (e.g., orthophosphate, peptides), which exhibit narrow EPR signals (small zero-field splitting). In contrast, Mn2+ ions in IR-sensitive cells, which are inefficient at DSB repair, exist largely as low-symmetry (L) complexes with substantially broadened spectra seen with enzymes and strongly chelating ligands. The fraction of cellular Mn2+ present as H-complexes (H-Mn2+), as measured by EPR of live, nonirradiated Mn-replete cells, is now the strongest known gauge of biological IR resistance between and within organisms representing all three domains of life: Antioxidant H-Mn2+ complexes, not antioxidant enzymes (e.g., Mn superoxide dismutase), govern IR survival. As the pool of intracellular metabolites needed to form H-Mn2+ complexes depends on the nutritional status of the cell, we conclude that IR resistance is predominantly a metabolic phenomenon. In a cross-kingdom analysis, the vast differences in taxonomic classification, genome size and radioresistance between cell types studied here support that IR resistance is not controlled by the repertoire of DNA repair and antioxidant enzymes. [ABSTRACT FROM AUTHOR]

The radioprotective capacity of a rationally-designed Mn2+-decapeptide complex (MDP), based on Mn antioxidants in the bacterium Deinococcus radiodurans, was investigated in a mouse model of radiation injury. MDP was previously reported to be extraordinarily radioprotective of proteins in the setting of vaccine development. The peptide-component (DEHGTAVMLK) of MDP applied here was selected from a group of synthetic peptides screened in vitro for their ability to protect cultured human cells and purified enzymes from extreme damage caused by ionizing radiation (IR). We show that the peptides accumulated in Jurkat T-cells and protected them from 100 Gy. MDP preserved the activity of T4 DNA ligase exposed to 60,000 Gy. In vivo, MDP was nontoxic and protected B6D2F1/J (female) mice from acute radiation syndrome. All irradiated mice treated with MDP survived exposure to 9.5 Gy (LD70/30) in comparison to the untreated mice, which displayed 63% lethality after 30 days. Our results show that MDP provides early protection of white blood cells, and attenuates IR-induced damage to bone marrow and hematopoietic stem cells via G-CSF and GM-CSF modulation. Moreover, MDP mediated the immunomodulation of several cytokine concentrations in serum including G-CSF, GM-CSF, IL-3 and IL-10 during early recovery. Our results present the necessary prelude for future efforts towards clinical application of MDP as a promising IR countermeasure. Further investigation of MDP as a pre-exposure prophylactic and post-exposure therapeutic in radiotherapy and radiation emergencies is warranted. [ABSTRACT FROM AUTHOR]