Ionizing-radiation-resistant Kocuria rhizophila PT10 isolated from the Tunisian Sahara xerophyte Panicum turgidum: Polyphasic characterization and proteogenomic arsenal.

A new strain belonging to the genus Kocuria, designed PT10, was isolated from irradiated roots of the xerophyte Panicum turgidum. Isolate PT10 is a Gram-positive, coccoid, aerobic and ionizing-radiation (IR)-resistant actinobacterium. PT10 has shown an ability to survive under extreme conditions, such as gamma irradiation, desiccation and high concentration of hydrogen peroxide. Phenotypic, chemotaxonomic and comparative genome analyses support the assignment of strain PT10 (LMG 31102 = DSM 108617) as Kocuria rhizophila. The complete genome sequence of PT10 consists of one chromosome (2,656,287 bps), with a 70.7% G + C content and comprises 2481 protein-coding sequences. A total of 1487 proteins were identified by LC-MS/MS profiling. In silico analyses revealed that the proteome of the oxidation-tolerant PT10 possesses several features explaining its IR-resistant phenotype and many adaptive pathways implicated in response to environmental pressures - desiccation, cold, reactive oxygen species and other stressors.

Photolyases and Cryptochromes in UV-resistant Bacteria from High-altitude Andean Lakes.

"High-altitude Andean Lakes" (HAAL) are pristine environments harboring poly-extremophilic microbes that show combined adaptations to physical and chemical stress such as large daily ambient thermal amplitude, extreme solar radiation levels, intense dryness, alkalinity, high concentrations of arsenic (up to 200 ppm) and dissolved salts. In this work, we compared the UV resistance profiles, pigment content and photoreactivation abilities of three UV-resistant bacteria isolated from distinct niches from HAALs, that is Acinetobacter sp. Ver3 (water, Lake Verde; 4400 m), Exiguobacterium sp. S17 (stromatolite, Lake Socompa, 3570 m) and Nesterenkonia sp. Act20 (soil, Lake Socompa, 3570 m). UV resistance ability of HAAL's strains indicate a clear adaptation to high radiation exposure encountered in their original habitat, which can be explained by genetic and physiological mechanisms named as the UV-resistome. Thus, the UV-resistome depends on the expression of a diverse set of genes devoted to evading or repairing the damage it provoked direct or indirectly. As pigment extraction and photoreactive assays indicate the presence of photoactive molecules, we characterized more in detail proteins with homology to photolyases/cryptochromes members (CPF). Phylogenetic analyses, sequence comparison and 3D modeling with bona fide CPF members were used to prove the presence of functional domains and key residues in the novel proteins.

Effect of ultrasound on the physicochemical and microbiological characteristics of Italian salami.

Italian salami were sonicated in different times (0, 3, 6 and 9min) using ultrasound bath (US, 25kHz). The effect of sonication on microbial growth (lactic acid bacteria and Micrococcaceae), lipid and protein oxidation, total heme pigments (THP), non heme iron (NHI) and metmyoglobin (MMb) was investigated during processing (0, 2, 15, and 28days) and storage (1, 30, and 120days). US enhanced growth of microorganisms (P<0.05), mainly for the treatment 9min of sonication. The lipid (peroxide value and TBARS) and protein (thiol group) oxidative reactions were accelerated by US (P<0.05) and they should be considered to maintain Italian salami quality. Sonication contributed to maintenance of THP (P<0.05), especially during storage. MMb pigment was not affected by sonication (P>0.05). This study presented some features of US application that could be explored in the manufacture of Italian salami.

Study of marine bacteria inactivation by photochemical processes: disinfection kinetics and growth modeling after treatment.

The importance of seawater treatment in order to avoid microbiological pollution related to aquaculture or ballast water management has increased during the last few years. Bacterial indicators used for the evaluation of different disinfection treatments are usually related with both waste and drinking water, these standards are not usual microorganisms found in seawater. Thus, it is thought necessary to study the behavior of different marine-specific organisms in regard to improve the disinfection processes in seawater. In this study, three different bacteria have been selected among major groups of bacterial community from marine waters: two water-associated, Roseobacter sp. and Pseudomonas litoralis, and one sediment-associated, Kocuria rhizophila. A kinetic inactivation model together with a post-treatment growth tendency has been obtained after the application of UV-C and UV/H2O2 processes. According to the first kinetic rate constant, different responses were obtained for the different bacterial groups. Once the treatment was applied, modeling of growth curves revealed high recover within the first 3 days after treatment, even when UV/H2O2 was applied. This study introduces a sensitivity index, in which results show different levels of resistance for both treatments, being Roseobacter sp. the most sensitive bacteria, followed by P. litoralis and K. rhizophila.

Isolation a new strain of Kocuria rosea capable of tolerating extreme conditions.

A new actinobacterial strain was isolated from Ab-e-Siah spring (dark water) taken from the Ramsar city in Iran, and subjected to several stress conditions investigation. The isolate, named MG2 strain, was Gram-positive, aerobic, diplococci or tetrad shaped, non-spore forming and non-motile. Phylogenetic analysis of the isolate using 16S rDNA sequence indicated that the organism matched best with the genus Kocuria and the highest sequence similarities (98.55%) being found with Kocuria rosea. The 16S rDNA sequence determined in this study has been deposited in the NCBI database with the accession no. JX534199, K. rosea strain MG2. The isolated strain was an alkaliphilic-mesophilic bacterium because the optimal growth was observed at pH 9.2 and temperature of 28 °C under aerobic condition. MG2 was a halotolerant strain and tolerated maximally to 15% NaCl concentraion. Viability analysis by flow cytometry indicated that this strain had highly resistance to UV-C radiation and moderately resistance to desiccation after 28 days. The viability of K. rosea strains MG2 and Deinococcus radiodurans R1 were determined D87 and D98 according to D index, respectively, by a dose radiation 25 J/cm (Appukuttan et al., 2006). Thus the UV resistance of strain MG2 was comparable with representative radiation resistant Deinococcus. Also MG2 was grown at 1-4% of H2O2 as an oxidant agent. This research is the first study on multiple extreme resistance of Kocuria rosea new strain (MG2) isolated in Iran.

Radio-resistance in psychrotrophic Kocuria sp. ASB 107 isolated from Ab-e-Siah radioactive spring.

A new isolate, Kocuria sp. ASB 107 from the Ab-e-Siah mineral radioactive spring (Ramsar, Mazandaran Province, Iran) was characterized on the basis of morphological and biochemical characteristics plus 16S rRNA gene sequencing. The isolate is most closely related to Kocuria rosea DSM 20447(T) (99.7% sequence similarity) and Kocuria polaris DSM 14382(T) (99.5%). This strain has some resistance to various genotoxic stresses, such as ionizing radiation, ultraviolet (256 nm- UV) and corona discharge. The 90% lethal doses (D(10)) for gamma-rays and 256 nm-UV are 2 kGy and 400 J m(-2), respectively, in definite cell concentration. Moreover, the resistance for a definite energy of corona discharge is 10 s, about 10 times greater than that of Escherichia coli. The growth temperature of the strain ASB 107 is 0-37 °C in TSB (tryptic soy broth). This study is the first report on the psychrotrophic radio-resistant bacteria belonging to the Kocuria genus isolated from Ab-e-Siah spring.

The relationship between carotenoids and sunlight response in members of the family Micrococcaceae.

The aim of this study was to compare the photoprotective effect of carotenoids in phylogentically related bacteria, which synthesize structurally different pigments. Two organisms were isolated from the same environment. Their 16S rDNA sequences and phenotypic characteristics identified them as members of the family Micrococcaceae. Reverse phase HPLC and absorption spectroscopy revealed that one of them, designated RMB40, synthesized 3 carotenoids with 9 conjugated double bonds, whilst the other, designated RMB42, synthesized a single and more hydrophobic pigment carrying 11 conjugated double bonds. Survival curves were obtained during sunlight exposure for both organisms and for carotenoid deficient mutants derived from them. Increased sunlight sensitivity was found in the carotenoidless mutant derived from RMB42. In contrast, pigment depletion had no appreciable effect on the sunlight response of RMB40. It is concluded that the structure of bacterial carotenoid probably exert an important influence on the effectiveness of these compounds to provide photoprotection in vivo.

Multiple-stress tolerance of ionizing radiation-resistant bacterial isolates obtained from various habitats: correlation between stresses.

Isolation of five ionizing radiation (IR)-resistant bacteria by screening of isolates from various habitats classified as common and stressed is reported. IR-resistant isolates exhibited varying degrees of resistance to gamma-radiation and were classified as highly and moderately radiation resistant. Resistance to ultraviolet (UV) radiation correlated well with gamma-radiation resistance, whereas a comparable desiccation resistance for all the highly and moderately radiation-resistant isolates was observed. However, salt tolerance failed to correlate with IR resistance, indicating a divergent evolution of the salt tolerance and radiation resistance. Characterization of isolates by the amplified rDNA restriction analysis profiling attested to the clustering of these isolates with their stress phenotype. 16S rRNA gene-based analysis of the isolates showed that the bacteria with similar-resistance physiologies clustered together and belonged to related genera. Hydrogen peroxide resistance and mitomycin survival patterns of the isolates indicated the roles of oxidative-stress tolerance in desiccation survival and recombination repair in higher radiation resistance, respectively.

Gamma irradiation and cellular damage in Kocuria rosea: investigation by one- and two-dimensional infrared spectroscopy.

Fourier transform infrared (FT-IR) spectroscopy was used to investigate the radiation-induced effects on Kocuria rosea. Bacterial suspensions at the stationary phase were exposed to increasing doses of gamma radiation. In the region 1350-840cm(-1), assigned to phosphodiester backbone, nucleic acids, and sugar rings, the radical damaging effects were dose-dependent, with the first threshold at 2.75kGy and the second at 13.75kGy inducing more striking spectral variations. Postirradiation reincubation did not significantly affect the biomolecular response, except in the spectral range 1100-1000cm(-1). These observations suggest the occurrence of new phylogenetic characteristics for K. rosea following irradiation. Moreover, two-dimensional analysis was used to highlight correlated evolutions of molecular species as radical aggression increased. The results point to an evolutionary scheme during the time course of irradiation. Thus, one- and two-dimensional IR analyses are convenient means of investigating the metabolic events following oxidative stress generated by either chemical or physical agents.

The antimicrobial effect of narrow-band UVB (313 nm) and UVA1 (345-440 nm) radiation in vitro.

Two new UV lamps were investigated with respect to their antibacterial effectiveness in vitro. Propioni (n = 20 strains) and Micrococcaceae (n = 16 strains) bacteria extracted from acne patients were applied to RCM and sheep blood agar plates and irradiated with a narrow-band UVB lamp (TL 100W/10R) at a wavelength of 313 nm and a UVA1 lamp (TL 01) at a wavelength of 345-440 nm. The precisely defined energy levels were, in the case of narrow-band UVB, 0.00, 0.30, 0.50, 1.00, 2.00 and 3.00 J/cm2 and, in the case of UVA1, 0.00, 2.50, 5.00, 7.50, 10.00 and 20.00 J/cm2. UVA1 inhibited neither the growth of Propioni nor Micrococcaceae bacteria. In contrast, the growth of Micrococcaceae was inhibited already at a dosage of 0.30 J/cm2 of narrow-band UVB (P < 0.05), highly significant from 0.50 J/cm2 (P < 0.01) and to a maximum of 2.2 powers of 10 at 3.00 J/cm2 compared with non-radiated control plates. Propioni bacteria were significantly inhibited at the minimum dosage of 0.30 J/cm2 of narrow-band UVB (P < 0.01) and to a maximum of 2.8 powers of 10 at 3.00 J/cm2.

DNA repair in the extremely radioresistant bacterium Deinococcus radiodurans.

Deinococcus radiodurans and other members of the same genus share extraordinary resistance to the lethal and mutagenic effects of ionizing and u.v. radiation and to many other agents that damage DNA. While it is known that this resistance is due to exceedingly efficient DNA repair, the molecular mechanisms responsible remain poorly understood. Following very high exposures to u.v. irradiation (e.g. 500 J m-2, which is non-lethal to D. radiodurans), this organism carries out extremely efficient excision repair accomplished by two separate nucleotide excision repair pathways acting simultaneously. One pathway requires the uvrA gene and appears similar to the UvrABC excinuclease pathway defined in Escherichia coli. The other excision repair pathway is specific for u.v. dimeric photoproducts, but is not mediated by a pyrimidine dimer DNA glycosylase. Instead, it is initiated by a second bona fide endonuclease that may recognize both pyrimidine dimers and pyrimidine-(6-4)pyrimidones. After high doses of ionizing-radiation (e.g. 1.5 Mrad), D. radiodurans can mend > 100 double-strand breaks (dsb) per chromosome without lethality or mutagenesis. Both dsb mending and survival are recA-dependent, indicating that efficient dsb mending proceeds via homologous recombination. D. radiodurans contains multiple chromosomes per cell, and it is proposed that dsb mending requires extensive recombination amongst these chromosomes, a novel phenomenon in bacteria. Thus, D. radiodurans may serve as an easily accessible model system for the double-strand-break-initiated interchromosomal recombination that occurs in eukaryotic cells during mitosis and meiosis.

[Sterilization by ionizing radiations (author's transl)]. / La stérilisation par les rayonnements ionisants

The first part summarizes the general characteristics of ionizing radiations and their activity on microorganisms: lethal and mutagenic effects, sensitivity conditions. Different microbial species have different sensitivities: gram negative bacteria are more sensitive (D10 approximately 5-10 Krads), bacterial spores and viruses are more resistant (D10 approximately 1 Megarads). The second part considers the main applications of radiosterilization: some are at present in full development (medical and surgical disposable equipment); others are still at the experimental stage. Practical aspects, determination of sterilizing doses and control of radiosterilization are also described.