Radiation-resistant Bacterium Research Articles

Hsp20, a small heat shock protein of Deinococcus radiodurans, confers tolerance to hydrogen peroxide in Escherichia coli.

The present study shows that DR1114 (Hsp20), a small heat shock protein of the radiationresistant bacterium Deinococcus radiodurans, enhances tolerance to hydrogen peroxide (H2O2) stress when expressed in Escherichia coli. A protein profile comparison showed that E. coli cells overexpressing D. radiodurans Hsp20 (EC-pHsp20) activated the redox state proteins, thus maintaining redox homeostasis. The cells also showed increased expression of pseudouridine (psi) synthases, which are important to the stability and proper functioning of structural RNA molecules. We found that the D. radiodurans mutant strain, which lacks a psi synthase (DR0896), was more sensitive to H2O2 stress than wild type. These suggest that an increased expression of proteins involved in the control of redox state homeostasis along with more stable ribosomal function may explain the improved tolerance of EC-pHsp20 to H2O2 stress.

Diversity of ionizing radiation-resistant bacteria obtained from the Taklimakan Desert.

So far, little is known about the diversity of the radiation-resistant microbes of the hyperarid Taklimakan Desert. In this study, ionizing radiation (IR)-resistant bacteria from two sites in Xinjiang were investigated. After exposing the arid (water content of 0.8 ± 0.3%) and non-arid (water content of 21.3 ± 0.9%) sediment samples to IR of 3000 Gy using a (60)Co source, a total of 52 γ-radiation-resistant bacteria were isolated from the desert sample. The 16S rRNA genes of all isolates were sequenced. The phylogenetic tree places these isolates into five groups: Cytophaga-Flavobacterium-Bacteroides, Proteobacteria, Deinococcus-Thermus, Firmicutes, and Actinobacteria. Interestingly, this is the first report of radiation-resistant bacteria belonging to the genera Knoellia, Lysobacter, Nocardioides, Paracoccus, Pontibacter, Rufibacter and Microvirga. The 16s rRNA genes of four isolates showed low sequence similarities to those of the published species. Phenotypic analysis showed that all bacteria in this study are able to produce catalase, suggesting that these bacteria possess reactive oxygen species (ROS)-scavenging enzymes. These radiation-resistant bacteria also displayed diverse metabolic properties. Moreover, their radiation resistances were found to differ. The diversity of the radiation-resistant bacteria in the desert provides further ecological support for the hypothesis that the ionizing-radiation resistance phenotype is a consequence of the evolution of ROS-scavenging systems that protect cells against oxidative damage caused by desiccation.

The Essential Role of the Deinococcus radiodurans ssb Gene in Cell Survival and Radiation Tolerance

Recent evidence has implicated single-stranded DNA-binding protein (SSB) expression level as an important factor in microbial radiation resistance. The genome of the extremely radiation resistant bacterium Deinococcus radiodurans contains genes for two SSB homologs: the homodimeric, canonical Ssb, encoded by the gene ssb, and a novel pentameric protein encoded by the gene ddrB. ddrB is highly induced upon exposure to radiation, and deletions result in decreased radiation-resistance, suggesting an integral role of the protein in the extreme resistance exhibited by this organism. Although expression of ssb is also induced after irradiation, Ssb is thought to be involved primarily in replication. In this study, we demonstrate that Ssb in D. radiodurans is essential for cell survival. The lethality of an ssb deletion cannot be complemented by providing ddrB in trans. In addition, the radiation-sensitive phenotype conferred by a ddrB deletion is not alleviated by providing ssb in trans. By altering expression of the ssb gene, we also show that lower levels of transcription are required for optimal growth than are necessary for high radiation resistance. When expression is reduced to that of E. coli, ionizing radiation resistance is similarly reduced. UV resistance is also decreased under low ssb transcript levels where growth is unimpaired. These results indicate that the expression of ssb is a key component of both normal cellular metabolism as well as pathways responsible for the high radiation tolerance of D. radiodurans.

Hypothetical Proteins Present During Recovery Phase of Radiation Resistant Bacterium Deinococcus radiodurans are Under Purifying Selection

Deinococcus radiodurans has an unusual capacity to recover from intense doses of ionizing radiation. The DNA repair proteins of this organism play an important role in repairing the heavily damaged DNA by employing a novel mechanism of DNA double-strand break repair. An earlier report stated that genes of many of these repair proteins are under positive selection implying that these genes have a tendency to mutate, which in turn provides selective advantage to this bacterium. Several "hypothetical proteins" are also present during the recovery phase and some of them have also been shown for their roles in radiation resistance. Therefore, we tested the selection pressure on the genes encoding these poorly characterized proteins. Our results show that a number of "hypothetical proteins" present during the repair phase have structural adaptations compared to their orthologs and the genes encoding them as well as those for the DNA repair proteins present during this phase are under purifying selection. Evidence of purifying selection in these hypothetical proteins suggests that certain novel characteristics among these proteins are conserved and seem to be under functional constraints to perform important functions during recovery process after gamma radiation damage.

ParA encoded on chromosome II of Deinococcus radiodurans binds to nucleoid and inhibits cell division in Escherichia coli

Bacterial genome segregation and cell division has been studied mostly in bacteria harbouring single circular chromosome and low-copy plasmids. Deinococcus radiodurans, a radiation-resistant bacterium, harbours multipartite genome system. Chromosome I encodes majority of the functions required for normal growth while other replicons encode mostly the proteins involved in secondary functions. Here, we report the characterization of putative P-loop ATPase (ParA2) encoded on chromosome II of D. radiodurans. Recombinant ParA2 was found to be a DNA-binding ATPase. E. coli cells expressing ParA2 showed cell division inhibition and mislocalization of FtsZ-YFP and those expressing ParA2-CFP showed multiple CFP foci formation on the nucleoid. Although, in trans expression of ParA2 failed to complement SlmA loss per se, it could induce unequal cell division in slmAminCDE double mutant. These results suggested that ParA2 is a nucleoid-binding protein, which could inhibits cell division in E. coli by affecting the correct localization of FtsZ and thereby cytokinesis. Helping slmAminCDE mutant to produce minicells, a phenotype associated with mutations in the 'Min' proteins, further indicated the possibility of ParA2 regulating cell division by bringing nucleoid compaction at the vicinity of septum growth.

There are more small amino acids and fewer aromatic rings in proteins of ionizing radiation-resistant bacteria

The identification of specific amino acids (AAs) or groups of functionally important AA residues in ionizing radiation-resistant bacteria (IRRB) is an important challenge in understanding the biological basis of resistance to ionizing radiation (IR; X-rays and gamma-rays). To address this problem, we compared homologous sites in multiple alignments of proteins of IRRB and IR-sensitive bacteria (IRSB) using the DeltaProt Toolbox. Substitution patterns were used as evidence for selection of certain AAs over others. Our results show that, in contrast to aromatic AAs, small/tiny AAs tend to be preferred in IRRB compared to IRSB. In agreement with previous experimental data showing that oxidation of AA residues is causative in the killing of irradiated cells and that IR resistance is correlated with the accumulation of divalent manganese ions (Mn2+)–peptide–orthophosphate (Pi) complexes, we proposed a chemical interpretation based on the Hard and Soft (Lewis) Acids and Bases (HSAB) concept. These findings should assist future efforts in selecting mutations for rational design of proteins with enhanced IR tolerance properties.

Kineococcus radiotolerans Dps forms a heteronuclear Mn–Fe ferroxidase center that may explain the Mn-dependent protection against oxidative stress

BackgroundThe ferroxidase center of DNA-binding protein from starved cells (Dps) is a major player in the iron oxidation/detoxification process that leads to a decreased reactive oxygen species production. The possible Mn(II) participation in this process has been studied in Dps from Kineococcus radiotolerans, a radiation-resistant bacterium with a high cytosolic Mn/Fe ratio and a high capacity to survive ionizing and stress conditions. MethodsThe X-ray structure of recombinant K. radiotolerans Dps loaded with Mn(II) has been solved at 2.0Å resolution. Mn(II) binding to K. radiotolerans Dps and its effect on Fe(II) oxidation have been characterized in spectroscopic measurements. ResultsIn K. radiotolerans Dps, the Fe–Fe ferroxidase center can have a Mn–Fe composition. Mn(II) binds only at the high affinity, so-called A site, whereas Fe(II) binds also at the low affinity, so-called B site. The Mn–Fe and Fe–Fe centers behave distinctly upon iron oxidation by O2. A site-bound Mn(II) or Fe(II) plays a catalytic role, while B site-bound Fe(II) behaves like a substrate and can be replaced by another Fe(II) after oxidation. When H2O2 is the Fe(II) oxidant, single electrons are transferred to aromatic residues near the ferroxidase center and give rise to intra-protein radicals thereby limiting OH release in solution. The presence of the Mn–Fe center results in significant differences in the development of such intra-protein radicals. ConclusionsMn(II) bound at the Dps ferroxidase center A site undergoes redox cycling provided the B site contains Fe. General significanceThe results provide a likely molecular mechanism for the protective role of Mn(II) under oxidative stress conditions as it participates in redox cycling in the hetero-binuclear ferroxidase center.

In Situ Determination of Manganese(II) Speciation in Deinococcus radiodurans by High Magnetic Field EPR: DETECTION OF HIGH LEVELS OF Mn(II) BOUND TO PROTEINS

High magnetic field high frequency electron paramagnetic resonance techniques were used to measure in situ Mn(II) speciation in Deinococcus radiodurans, a radiation-resistant bacteria capable of accumulating high concentrations of Mn(II). It was possible to identify and quantify the evolution of Mn(II) species in intact cells at various stages of growth. Aside from water, 95-GHz high field electron nuclear double resonance showed that the Mn(II) ions are bound to histidines and phosphate groups, mostly from fructose-1,6-bisphosphate but also inorganic phosphates and nucleotides. During stationary growth phase, 285-GHz continuous wave EPR measurements showed that histidine is the most common ligand to Mn(II) and that significant amounts of cellular Mn(II) in D. radiodurans are bound to peptides and proteins. As much as 40% of the total Mn(II) was in manganese superoxide dismutase, and it is this protein and not smaller manganese complexes, as has been suggested recently, that is probably the primary defense against superoxide.

Functional Characterization of the Role of the Chromosome I Partitioning System in Genome Segregation in Deinococcus radiodurans

Deinococcus radiodurans, a radiation-resistant bacterium, harbors a multipartite genome. Chromosome I contains three putative centromeres (segS1, segS2, and segS3), and ParA (ParA1) and ParB (ParB1) homologues. The ParB1 interaction with segS was sequence specific, and ParA1 was shown to be a DNA binding ATPase. The ATPase activity of ParA1 was stimulated when segS elements were coincubated with ParB1, but the greatest increase was observed with segS3. ParA1 incubated with the segS-ParB1 complex showed increased light scattering in the absence of ATP. In the presence of ATP, this increase was continued with segS1-ParA1B1 and segS2-ParA1B1 complexes, while it decreased rapidly after an initial increase for 30 min in the case of segS3. D. radiodurans cells expressing green fluorescent protein (GFP)-ParB1 produced foci on nucleoids, and the ΔparB1 mutant showed growth retardation and ∼13%-higher anucleation than the wild type. Unstable mini-F plasmids carrying segS1 and segS2 showed inheritance in Escherichia coli without ParA1B1, while segS3-mediated plasmid stability required the in trans expression of ParA1B1. Unlike untransformed E. coli cells, cells harboring pDAGS3, a plasmid carrying segS3 and also expressing ParB1-GFP, produced discrete GFP foci on nucleoids. These findings suggested that both segS elements and the ParA1B1 proteins of D. radiodurans are functionally active and have a role in genome segregation.

Significant Rewiring of the Transcriptome and Proteome of an Escherichia coli Strain Harboring a Tailored Exogenous Global Regulator IrrE

Cell reprogramming for microorganisms via engineered or artificial transcription factors and RNA polymerase mutants has presented a powerful tool for eliciting complex traits that are practically useful particularly for industrial strains, and for understanding at the global level the regulatory network of gene transcription. We previously further showed that an exogenous global regulator IrrE (derived from the extreme radiation-resistant bacterium Deinococcus radiodurans) can be tailored to confer Escherichia coli (E. coli) with significantly enhanced tolerances to different stresses. In this work, based on comparative transcriptomic and proteomic analyses of the representative strains E1 and E0, harboring the ethanol-tolerant IrrE mutant E1 and the ethanol-intolerant wild type IrrE, respectively, we found that the transcriptome and proteome of E. coli were extensively rewired by the tailored IrrE protein. Overall, 1196 genes (or approximately 27% of E. coli genes) were significantly altered at the transcriptomic level, including notably genes in the nitrate-nitrite-nitric oxide (NO) pathway, and genes for non-coding RNAs. The proteomic profile revealed significant up- or downregulation of several proteins associated with syntheses of the cell membrane and cell wall. Analyses of the intracellular NO level and cell growth under reduced temperature supported a close correlation between NO and ethanol tolerance, and also suggests a role for membrane fluidity. The significantly different omic profiles of strain E1 indicate that IrrE functions as a global regulator in E. coli, and that IrrE may be evolved for other cellular tolerances. In this sense, it will provide synthetic biology with a practical and evolvable regulatory “part” that operates at a higher level of complexity than local regulators. This work also suggests a possibility of introducing and engineering other exogenous global regulators to rewire the genomes of microorganism cells.

Preserving Immunogenicity of Lethally Irradiated Viral and Bacterial Vaccine Epitopes Using a Radio- Protective Mn2+-Peptide Complex from Deinococcus

Although pathogen inactivation by γ-radiation is an attractive approach for whole-organism vaccine development, radiation doses required to ensure sterility also destroy immunogenic protein epitopes needed to mount protective immune responses. We demonstrate the use of a reconstituted manganous peptide complex from the radiation-resistant bacterium Deinococcus radiodurans to protect protein epitopes from radiation-induced damage and uncouple it from genome damage and organism killing. The Mn(2+) complex preserved antigenic structures in aqueous preparations of bacteriophage lambda, Venezuelan equine encephalitis virus, and Staphylococcus aureus during supralethal irradiation (25-40 kGy). An irradiated vaccine elicited both antibody and Th17 responses, and induced B and T cell-dependent protection against methicillin-resistant S. aureus (MRSA) in mice. Structural integrity of viruses and bacteria are shown to be preserved at radiation doses far above those which abolish infectivity. This approach could expedite vaccine production for emerging and established pathogens for which no protective vaccines exist.

Structure and Cellular Dynamics of Deinococcus radiodurans Single-stranded DNA (ssDNA)-binding Protein (SSB)-DNA Complexes

The single-stranded DNA (ssDNA)-binding protein from the radiation-resistant bacterium Deinococcus radiodurans (DrSSB) functions as a homodimer in which each monomer contains two oligonucleotide-binding (OB) domains. This arrangement is exceedingly rare among bacterial SSBs, which typically form homotetramers of single-OB domain subunits. To better understand how this unusual structure influences the DNA binding and biological functions of DrSSB in D. radiodurans radiation resistance, we have examined the structure of DrSSB in complex with ssDNA and the DNA damage-dependent cellular dynamics of DrSSB. The x-ray crystal structure of the DrSSB-ssDNA complex shows that ssDNA binds to surfaces of DrSSB that are analogous to those mapped in homotetrameric SSBs, although there are distinct contacts in DrSSB that mediate species-specific ssDNA binding. Observations by electron microscopy reveal two salt-dependent ssDNA-binding modes for DrSSB that strongly resemble those of the homotetrameric Escherichia coli SSB, further supporting a shared overall DNA binding mechanism between the two classes of bacterial SSBs. In vivo, DrSSB levels are heavily induced following exposure to ionizing radiation. This accumulation is accompanied by dramatic time-dependent DrSSB cellular dynamics in which a single nucleoid-centric focus of DrSSB is observed within 1 h of irradiation but is dispersed by 3 h after irradiation. These kinetics parallel those of D. radiodurans postirradiation genome reconstitution, suggesting that DrSSB dynamics could play important organizational roles in DNA repair.

DR2417, a hypothetical protein characterized as a novel β-CASP family nuclease in radiation resistant bacterium, Deinococcus radiodurans

BackgroundDeinococcus radiodurans survives extreme doses of radiations contributed by efficient DNA repair pathways. DR2417 (DncA) was detected separately both in a pool of nucleotide binding proteins and multiprotein complex isolated from cells undergoing DNA repair. Scope of reviewDR_2417m ORF was sequenced and amino acid sequence of DncA was search for structural similarities with other proteins and functional motifs. Recombinant DncA was characterized for its DNA metabolic functions in vitro and its role in radiation resistance. Major conclusionsSequencing of DR_2417m did not show the reported frame shift at 996th nucleotide position of this gene. DncA showed similarities with β-CASP family nucleases. Recombinant protein acted efficiently on dsDNA and showed an Mn2+ dependent 3′→5′ exonuclease and ssDNA/dsDNA junction endonuclease activities while a very low level activity on RNA. The DNase activity of this protein was inhibited in presence of ATP. Its transcription was induced upon γ radiation exposure and a reduction in its copy number resulted in reduced growth rate and loss of γ radiation resistance in Deinococcus. Conclusion — our results suggest that DncA was a novel nuclease of β CASP family having a strong dsDNA end processing activity and it seems to be an essential gene required for both growth and γ radiation resistance of this bacterium. General significanceTraditionally DncA should have shown both DNase and RNase functions as other members of β CASP family nucleases. A strong DNase and poor RNase activity possibly made it functionally significant in the radioresistance of D. radiodurans, which would be worth investigating independently.

Function and biochemical characterization of RecJ in Deinococcus radiodurans

The single-stranded DNA-specific nuclease RecJ is found in most bacteria where it is involved in the RecFOR double-stranded break (DSBs) repair pathway. DSBs repair mainly occurs via the RecFOR pathway in Deinococcus radiodurans, a well-known radiation-resistant bacterium. A recJ null mutant was constructed to investigate the role of recJ in D. radiodurans. recJ inactivation caused growth defects and sensitivity to high temperatures. However, the radiation resistance of the recJ mutant was only moderately decreased. The full-length D. radiodurans RecJ (DrRecJ) protein was expressed and purified to further characterize its biochemical properties. DrRecJ possessed a Mn2+ concentration-dependent nuclease activity where the optimal Mn2+ concentration was 0.1mM. DrRecJ had a similar activity profile after adding 10mM Mg2+ to reactions with different Mn2+ concentrations, indicating that Mn2+ is a RecJ regulator. Escherichia coli RecJ has no activity on 5′ ssDNA tails shorter than 6-nt, but DrRecJ could effectively degrade DNA with a 4-nt 5′ ssDNA tail, suggesting that DrRecJ may have a wider range of DNA substrates. Moreover, SSB in D. radiodurans stimulated the DrRecJ exonuclease activity, whereas DdrB inhibited it and provided protection to ssDNA. Overall, our results indicate that recJ is a nonessential gene in D. radiodurans and that the activity of DrRecJ is regulated by Mn2+ and SSB-DdrB.

Role of Mn2+ and compatible solutes in the radiation resistance of thermophilic bacteria and archaea.

Radiation-resistant bacteria have garnered a great deal of attention from scientists seeking to expose the mechanisms underlying their incredible survival abilities. Recent analyses showed that the resistance to ionizing radiation (IR) in the archaeon Halobacterium salinarum is dependent upon Mn-antioxidant complexes responsible for the scavenging of reactive oxygen species (ROS) generated by radiation. Here we examined the role of the compatible solutes trehalose, mannosylglycerate, and di-myo-inositol phosphate in the radiation resistance of aerobic and anaerobic thermophiles. We found that the IR resistance of the thermophilic bacteria Rubrobacter xylanophilus and Rubrobacter radiotolerans was highly correlated to the accumulation of high intracellular concentration of trehalose in association with Mn, supporting the model of Mn2+-dependent ROS scavenging in the aerobes. In contrast, the hyperthermophilic archaea Thermococcus gammatolerans and Pyrococcus furiosus did not contain significant amounts of intracellular Mn, and we found no significant antioxidant activity from mannosylglycerate and di-myo-inositol phosphate in vitro. We therefore propose that the low levels of IR-generated ROS under anaerobic conditions combined with highly constitutively expressed detoxification systems in these anaerobes are key to their radiation resistance and circumvent the need for the accumulation of Mn-antioxidant complexes in the cell.

Comparative Survival Analysis ofDeinococcus radioduransand the HaloarchaeaNatrialba magadiiandHaloferax volcaniiExposed to Vacuum Ultraviolet Irradiation

The haloarchaea Natrialba magadii and Haloferax volcanii, as well as the radiation-resistant bacterium Deinococcus radiodurans, were exposed to vacuum UV (VUV) radiation at the Brazilian Synchrotron Light Laboratory. Cell monolayers (containing 105 to 106 cells per sample) were prepared over polycarbonate filters and irradiated under high vacuum (10−5 Pa) with polychromatic synchrotron radiation. N. magadii was remarkably resistant to high vacuum with a survival fraction of (3.77±0.76)×10−2, which was larger than that of D. radiodurans (1.13±0.23)×10−2. The survival fraction of the haloarchaea H. volcanii, of (3.60±1.80)×10−4, was much smaller. Radiation resistance profiles were similar between the haloarchaea and D. radiodurans for fluences up to 150 J m−2. For fluences larger than 150 J m−2, there was a significant decrease in the survival of haloarchaea, and in particular H. volcanii did not survive. Survival for D. radiodurans was 1% after exposure to the higher VUV fluence (1350 J m−2), while N. magadii had a survival lower than 0.1%. Such survival fractions are discussed regarding the possibility of interplanetary transfer of viable microorganisms and the possible existence of microbial life in extraterrestrial salty environments such as the planet Mars and Jupiter's moon Europa. This is the first work to report survival of haloarchaea under simulated interplanetary conditions. Key Words: Vacuum ultraviolet—Synchrotron—Radiation resistance—Planetary protection—Panspermia. Astrobiology 11, 1034–1040.

The Structure and Enzymatic Properties of a Novel RNase II Family Enzyme from Deinococcus radiodurans

Exoribonucleases are vital in nearly all aspects of RNA metabolism, including RNA maturation, end-turnover, and degradation. RNase II and RNase R are paralogous members of the RNR superfamily of nonspecific, 3′→5′, processive exoribonucleases. In Escherichia coli, RNase II plays a primary role in mRNA decay and has a preference for unstructured RNA. RNase R, in contrast, is capable of digesting structured RNA and plays a role in the degradation of both mRNA and stable RNA. Deinococcus radiodurans, a radiation-resistant bacterium, contains two RNR family members. The shorter of these, DrR63, includes a sequence signature typical of RNase R, but we show here that this enzyme is an RNase II-type exonuclease and cannot degrade structured RNA. We also report the crystal structure of this protein, now termed DrII. The DrII structure reveals a truncated RNA binding region in which the N-terminal cold shock domains, typical of most RNR family nucleases, are replaced by an unusual winged helix–turn–helix domain, where the “wing” is contributed by the C-terminal S1 domain. Consistent with its truncated RNA binding region, DrII is able to remove 3′ overhangs from RNA molecules closer to duplexes than do other RNase II-type enzymes. DrII also displays distinct sensitivity to pyrimidine-rich regions of single-stranded RNA and is able to process tRNA precursors with adenosine-rich 3′ extensions in vitro. These data indicate that DrII is the RNase II of D. radiodurans and that its structure and catalytic properties are distinct from those of other related enzymes.

Survival of Deinococcus radiodurans Against Laboratory-Simulated Solar Wind Charged Particles

In this experimental study, cells of the radiation-resistant bacterium Deinococcus radiodurans were exposed to several different sources of radiation chosen to replicate the charged particles found in the solar wind. Naked cells or cells mixed with dust grains (basalt or sandstone) differing in elemental composition were exposed to electrons, protons, and ions to determine the probability of cell survival after irradiation. Doses necessary to reduce the viability of cell population to 10% (LD(10)) were determined under different experimental conditions. The results of this study indicate that low-energy particle radiation (2-4 keV), typically present in the slow component of the solar wind, had no effect on dehydrated cells, even if exposed at fluences only reached in more than 1000 years at Sun-Earth distance (1 AU). Higher-energy ions (200 keV) found in solar flares would inactivate 90% of exposed cells after several events in less than 1 year at 1 AU. When mixed with dust grains, LD(10) increases about 10-fold. These results show that, compared to the highly deleterious effects of UV radiation, solar wind charged particles are relatively benign, and organisms protected under grains from UV radiation would also be protected from the charged particles considered in this study.

Characterization of Deinococcus sahariens sp. nov., a radiation-resistant bacterium isolated from a Saharan hot spring

An ultraviolet-radiation-resistant, Gram-positive, orange-pigmented, thermophilic and strictly aerobic cocci was isolated from Saharan water hot spring in Tunisia. The newly isolated bacterium, designated HAN-23(T), was identified based on polyphasic taxonomy including genotypic, phenotypic and chemotaxonomic characterization. Phylogenetic analysis based on 16S rRNA gene sequences placed this strain within Deinococcus genus. However, strain HAN-23(T) is different from recognized species of the genus Deinococcus, showing less than 94.0% similarity values to its closest relatives. The predominant cellular fatty acids determined by gas chromatography were iso-C(15:0), iso-C(17:0) and iso C(17:1) ω9c. The major respiratory quinone was MK-8. The DNA G+C content was 66.9mol%. DNA-DNA hybridization measurements revealed low DNA relatedness (6%) between the novel isolate and its closest neighbor, the type strain Deinococcus geothermalis DSM 11300. On the basis of the phenotypic, chemotaxonomic and phylogenetic data, strain HAN-23(T) represents a novel species of the genus Deinococcus, for which the name Deinococcus sahariens sp. nov. is proposed, the type strain being HAN-23(T) (=DSM 18496(T); LMG 23756(T)).

PARG: A Macrodomain in Disguise

Our understanding of poly-ADP-ribosylation as a posttranslational modification was limited by the lack of structural information on poly-ADP-ribose (PAR) hydrolysing enzymes. A recent study in Nature (Slade etal., 2011) reports the structure of PAR glycohydrolase (PARG), revealing unexpected similarity to the ubiquitous ADP-ribose-binding macrodomains.