Radioresistant Species Research Articles

Soil Microbes and Plant-Associated Microbes in Response to Radioactive Pollution May Indirectly Affect Plants and Insect Herbivores: Evidence for Indirect Field Effects from Chernobyl and Fukushima.

The biological impacts of the nuclear accidents in Chernobyl (1986) and Fukushima (2011) on wildlife have been studied in many organisms over decades, mainly from dosimetric perspectives based on laboratory experiments using indicator species. However, ecological perspectives are required to understand indirect field-specific effects among species, which are difficult to evaluate under dosimetric laboratory conditions. From the viewpoint that microbes play a fundamental role in ecosystem function as decomposers and symbionts for plants, we reviewed studies on microbes inhabiting soil and plants in Chernobyl and Fukushima in an attempt to find supporting evidence for indirect field-specific effects on plants and insect herbivores. Compositional changes in soil microbes associated with decreases in abundance and species diversity were reported, especially in heavily contaminated areas of both Chernobyl and Fukushima, which may accompany explosions of radioresistant species. In Chernobyl, the population size of soil microbes remained low for at least 20 years after the accident, and the abundance of plant-associated microbes, which are related to the growth and defense systems of plants, possibly decreased. These reported changes in microbes likely affect soil conditions and alter plant physiology. These microbe-mediated effects may then indirectly affect insect herbivores through food-mass-mediated, pollen-mediated, and metabolite-mediated interactions. Metabolite-mediated interactions may be a major pathway for ecological impacts at low pollution levels and could explain the decreases in insect herbivores in Fukushima. The present review highlights the importance of the indirect field effects of long-term low-dose radiation exposure under complex field circumstances.

Contamination analysis of Arctic ice samples as planetary field analogs and implications for future life-detection missions to Europa and Enceladus

Missions to detect extraterrestrial life are being designed to visit Europa and Enceladus in the next decades. The contact between the mission payload and the habitable subsurface of these satellites involves significant risk of forward contamination. The standardization of protocols to decontaminate ice cores from planetary field analogs of icy moons, and monitor the contamination in downstream analysis, has a direct application for developing clean approaches crucial to life detection missions in these satellites. Here we developed a comprehensive protocol that can be used to monitor and minimize the contamination of Arctic ice cores in processing and downstream analysis. We physically removed the exterior layers of ice cores to minimize bioburden from sampling. To monitor contamination, we constructed artificial controls and applied culture-dependent and culture-independent techniques such as 16S rRNA amplicon sequencing. We identified 13 bacterial contaminants, including a radioresistant species. This protocol decreases the contamination risk, provides quantitative and qualitative information about contamination agents, and allows validation of the results obtained. This study highlights the importance of decreasing and evaluating prokaryotic contamination in the processing of polar ice cores, including in their use as analogs of Europa and Enceladus.

Codon usage bias in radioresistant bacteria.

The relationship between patterns of codon usage bias (CUB), the preferential usage of synonimous nucleotide triplets encoding the same amino acid, and radioresistance was investigated int he genomes of 16 taxonomically distinct radioresistant prokaryotic organisms and in a control set of 11 non-radioresistant bacteria. The radioresistant species were found to be strongly biased towards G and C in the third synonimous codon position. ENC and neutrality plots also sugest that CUB in radioresistant bacteria is mainly affected by mutational bias. Furthermore, the availability of tRNA gene copy number was analyzed and it was found that nine radioresistant species have the sam number of tRNA gene copies for each codon. This suggests that tRNA gene copies and codon bias co-evolved in a specific way in radioresistant species.

Studies on the ontogenic radio-sensitivity in Callosobruchus species complex to establish a generic dose of phytosanitary irradiation as a post harvest quarantine treatment for disinfestation of pulses

The effects of gamma radiation were observed on the metamorphosis and reproduction as key target features to be intercepted for disinfestation of the three major pest bruchid species, Callosobruchus maculatus (Fabricius), C. analis (Fabricius) and C. chinensis (Linnaeus) irradiated in the various ontogenic stages. The present study was aimed to determine an efficacious generic dose of phytosanitary irradiation (PI) for bruchid disinfestation in pulses.Callosobruchus chinensis was the most radio-resistant species among the present tested species, and male bruchids were more radio-resistant than the females in this species complex.In this complex of tested bruchid species, the gamma dose required to cause 100% metamorphic disruption in the most radio-resistant pre-imaginal stage (pharate adult) was 20–46% higher than the dose required to induce complete sterility in the most radio-resistant imaginal stage (4–5 day old). The effective dose inducing 99.9% impact (ED99.9) was 105 Gy for sterility induction but ~181 Gy to induce metamorphic disruption in the most radio-resistant pre-imaginal pharate adult in C. chinensis, whereas the most radio-resistant imaginal stage (4–5 day old adult) of this species required 124 Gy for complete sterilization.Based on these results, 160–200 Gy as phytosanitary irradiation dose range was evaluated on a semi-large scale testing on the pigeonpea pulse seeds having mixed infestation of Callosobruchus species complex, which indicated that 200 Gy might be considered as a feasible generic dose of phytosanitary irradiation for bruchid disinfestation in pulses.

Adaptation of small mammals to radiocontaminated environment: Oxidative metabolism and radioresistance.

Differences in radioresistance and oxidative metabolism parameters in rodents of different ecological specialization in the East Ural radioactive trace (EURT) area are shown. Northern mole voles (radiosensitive species) exhibit a pronounced resistance to chronic exposure to radiation, living in a series of generations in a radioactive environment, whereas pigmy wood mice (radioresistant species) are less resistant in the EURT area due to their migration activity. Thus, under the EURT area conditions, northern mole voles realize the genotypic radioadaptation, whereas pigmy wood mice realize the physiological radioadaptation, the key role in which is played by the ecological and physiological characteristics and the lifestyle of animals.

Enhanced Radiation Resistance of Methanosarcina soligelidi SMA-21, a New Methanogenic Archaeon Isolated from a Siberian Permafrost-Affected Soil in Direct Comparison to Methanosarcina barkeri.

Permafrost-affected soils are characterized by a high abundance and diversity of methanogenic communities, which are considered suitable model organisms for potential life on Mars. Methanogens from Siberian permafrost have been proven to be highly resistant against divers stress conditions such as subzero temperatures, desiccation, and simulated thermophysical martian conditions. Here, we studied the radiation resistance of the currently described new species Methanosarcina soligelidi SMA-21, which was isolated from a Siberian permafrost-affected soil, in comparison to Methanosarcina barkeri, which is used as a reference organism from a nonpermafrost soil environment. Both strains were exposed to solar UV and ionizing radiation to assess their limits of survival. Methanosarcina soligelidi exhibit an increase in radiation resistance to UV (2.5- to 13.8-fold) and ionizing radiation (46.6-fold) compared to M. barkeri. The F10 (UVC) and D10 (X-rays) values of M. soligelidi are comparable to values for the well-known, highly radioresistant species Deinococcus radiodurans. In contrast, the radiation response of M. barkeri was highly sensitive to UV and ionizing radiation comparably to Escherichia coli and other radiosensitive microorganisms. This study showed that species of the same genus respond differently to UV and ionizing radiation, which might reflect the adaptation of Methanosarcina soligelidi SMA-21 to the harsh environmental conditions of the permafrost habitat. Methanogenic archaea-Environmental UV-Ionizing radiation-Permafrost-Radiation resistance-Mars.

Effects of Ionizing Radiation on Postharvest Fungal Pathogens.

Postharvest diseases cause losses in a wide variety of crops around the world. Irradiation, a useful nonchemical approach, has been used as an alternative treatment for fungicide to control plant fungal pathogens. For a preliminary study, ionizing radiations (gamma, X-ray, or e-beam irradiation) were evaluated for their antifungal activity against Botrytis cinerea, Penicillium expansum, and Rhizopus stolonifer through mycelial growth, spore germination, and morphological analysis under various conditions. Different fungi exhibited different radiosensitivity. The inhibition of fungal growth showed in a dose-dependent manner. Three fungal pathogens have greater sensitivity to the e-beam treatment compared to gamma or X-ray irradiations. The inactivation of individual fungal-viability to different irradiations can be considered between 3–4 kGy for B. cinerea and 1–2 kGy for P. expansum and R. stolonifer based on the radiosensitive and radio-resistant species, respectively. These preliminary data will provide critical information to control postharvest diseases through radiation.

Transcriptional analysis of Deinococcus radiodurans reveals novel small RNAs that are differentially expressed under ionizing radiation.

Small noncoding RNAs (sRNAs) are posttranscriptional regulators that have been identified in multiple species and shown to play essential roles in responsive mechanisms to environmental stresses. The natural ability of specific bacteria to resist high levels of radiation has been of high interest to mechanistic studies of DNA repair and biomolecular protection. Deinococcus radiodurans is a model extremophile for radiation studies that can survive doses of ionizing radiation of >12,000 Gy, 3,000 times higher than for most vertebrates. Few studies have investigated posttranscriptional regulatory mechanisms of this organism that could be relevant in its general gene regulatory patterns. In this study, we identified 199 potential sRNA candidates in D. radiodurans by whole-transcriptome deep sequencing analysis and confirmed the expression of 41 sRNAs by Northern blotting and reverse transcriptase PCR (RT-PCR). A total of 8 confirmed sRNAs showed differential expression during recovery after acute ionizing radiation (15 kGy). We have also found and confirmed 7 sRNAs in Deinococcus geothermalis, a closely related radioresistant species. The identification of several novel sRNAs in Deinococcus bacteria raises important questions about the evolution and nature of global gene regulation in radioresistance.

Ionising radiation and area-wide management of insect pests to promote sustainable agriculture. A review

Despite the liberal use of broad-spectrum insecticides to keep many insect pests of agricultural and veterinary importance at bay, food losses, both pre- and post-harvest, due to these insect pests contribute significantly to the high prevalence of undernourishment in the world. New, innovative pest control tactics and strategies are therefore needed that are both effective and not detrimental to the environment. As part of the arsenal of environmentally-friendly control tactics, the sterile insect technique (SIT) has proven to be a very effective tool against selected insect pests when used as part of an area-wide integrated pest management (AW-IPM) approach. Likewise, the use of natural enemies for augmentative or inundative biological control is now a major component of pest control in many parts of the world. Both control tactics are complementary and even synergistic under certain circumstances, but their combined use has so far not been applied on an operational scale. Ionising radiation can be readily employed to effectively and safely induce sexual sterility in insects. Although the sterile insect technique has often been associated with an eradication strategy, major advances in rearing efficiency, and improved handling and release methods, have made the use of sterile insects economically feasible for insect pest suppression, prevention or containment. Recently, more emphasis has been placed on the quality of the sterile insect once released in the field rather than mainly assessing quality in the rearing facility. This combined with other innovations such as the development of genetic sexing strains, better understanding the impact of radiation on radio-resistant species such as Lepidoptera and the development of the F1 sterility concept, advances in monitoring the induced sterility, etc. have significantly increased the efficiency of the sterile insect technique for several insect species. The action of sterile insects is inversely dependent on the density of the target population, and sterile insects have the intrinsic capacity to actively search for and mate with the last individuals of a pest population. These two characteristics make them ideal to deal with outbreaks of invasive insect pests. The use of sterile insects presents no threat to the environment, but aspects such as diet and waste disposal in large rearing facilities or bio-security in cases where the rearing facility is located in an area that is already free of the pest require the necessary attention. Ionising radiation can also be applied to greatly improve the efficiency of mass-rearing, handling and shipment of insect parasitoids and predators. Area-wide integrated pest management programmes that use sterile insects or natural enemies are complex and management-intensive, and require a management structure that is exclusively dedicated to the programme. Past and current examples have shown the enormous benefit-cost ratios that these programmes can generate and their importance for enhanced agriculture is increasing in significance.

Gamma Radiation Processing of Clam (Galatea Paradoxa Born 1778) from the Volta River Estuary for Microbiological Decontamination

The Clam (Galatea paradoxa Born 1778) is a dermesal dweller of riverine water and filter feed by passing water through gut concentrating particulate matter including bacteria in the gut and mantle. Microbial profile of contaminating bacteria and their sensitivity to gamma irradiation (0 – 20 kGy) were ascertained in vivo and in vitro under laboratory conditions. Conventional cul-tural and morphological characteristics were used to detect the resident Total Aerobic Bacteria (TAB), Total Heterotrophic and Total Coliform bacteria (TC) populations in the clam and the species encountered were confirmed using biochemical methods and the API 20E identification kit. Twenty (20) bacteria species in the samples belonged to 18 genera (Acinetobacter, Aeromo-nas, Chromobacterium, Citrobacter, Enterobacter, Escherichia, Flavobacterium, Klebsiella, Mi-crococcus, Morganella, Proteus, Pseudomonas, Salmonella, Serratia, Staphylococcus, Strepto-coccus, Vibrio and Yersinia) predominated by Acinetobacter (22%), Staphylococcus aureus (12%) and Klebsiella ornitholytica (11%) in the clam mantle and Pseudomonas aeruginosa (32%), Klebsiella ornitholytica (24%) and Flavobacterium meningosepticum (12%) in the water. A dose of 20 kGy eliminated all microorganisms in the “in vitro” studies; at 15 kGy only two bacteria species Micrococcus radiodurans and Vibrio cholera survived. The most radio resistant species was M. radiodurans (D10=6.19 kGy), followed by Vibrio cholera (D10=5.2 kGy). A dose of 10 kGy eliminated Staphylococcus aureus (D10=1.7 kGy). Practical implications from these find-ings are discussed in the light of food safety of preserved clams.

Microbial Extremophiles at the Limits of Life

Prokaryotic extremophiles were the first representatives of life on Earth and they are responsible for the genesis of geological structures during the evolution and creation of all currently known ecosystems. Flexibility of the genome probably allowed life to adapt to a wide spectrum of extreme environments. As a result, modern prokaryotic diversity formed in a framework of physico-chemical factors, and it is composed of: thermophilic, psychrophilic, acidophilic, alkaliphilic, halophilic, barophilic, and radioresistant species. This artificial systematics cannot reflect the multiple actions of different environmental factors since one organism could unite characteristics of several extreme-groups. In this review we show the current status of studies in all fields of extremophiles and summarize the limits of life for different species of microbial extremophiles. We also discuss the finding of extremophiles from unusual places such as soils, and briefly review recent studies of microfossils in meteorites in the context of the significance of microbial extremophiles to Astrobiology.

Detection of irradiation induced changes on the activity and diversity of soil microbial communities: The effect of soil type

Our aim was to measure the effects of irradiation treatments on soil communities from three different soils. Undisturbed soil cores from three temperate sites (deciduous and coniferous woodland and grassland) were irradiated to give cumulative doses from 0-160 Gy. Cores were incubated at 15 o C and three cores from each treatment sampled after <1, 3 and 8 d. Soil fungi and heterotrophic bacteria were enumerated and the activity and functional diversity of soil microbial communities assessed in terms of their potential to utilise a range of C-sources. Although no significant treatment effects were observed in the numbers of cultivable fungi or fast growing heterotrophic bacteria, the numbers of cultivable Pseudomonas spp. declined in all three soils after irradiation at 80 and 160 Gy. Microbial communities from the coniferous forest soil also showed a dramatic decrease in the metabolic activity and number of substrates utilised by after irradiation at 160 Gy. Gamma irradiation had a greater affect on microbial communities in the two organic forest soils as compared to the mineral grassland soil, this could be related to variations in the physico-chemical shielding properties and in the indigenous communities in terms of radio-resistant species.

Response of shortgrass plains vegetation to gamma radiation—III. Nine years of chronic irradiation

Native shortgrass vegetation was irradiated for 9 yr using 137Cs as a gamma source. Diversity changed rapidly during the first 2 yr with little change after. An exposure rate of 720 nC/kg sec (10 R/hr) decreased diversity by 50%. All vegetation was killed at an exposure rate of 3.6 μC/kg sec (50 R/hr). Gaura coccina and Carex heliophila were the most radioresistant species. Bouteloua gracilis, the dominant species, was relatively radioresistant and had an LD 50 of 240 nC/kg sec (3.3 R/hr). Species with underground meristems appeared to be more radioresistant than they were, due to shielding by the soil. Three species of annuals, Lepedium densiflorum, Cirsium undulatum and Sissymbrium altissimum, increased in density where the density of the dominant climax species was reduced due to the radiation. The lichen Parmelia chlorochroa had an LD 100 of between 340 and 520 nC/kg sec (4.8 and 7.2 R/hr) which was probably due to habitat changes, rather than direct radiation effects.

Survival Time Response of the Mongolian Gerbil after Total Body Irradiation

The overall survival-time response of the Mongolian gerbil (Meriones unguiculatus) to lethal and supralethal doses of x-radiation has been determined and found to be similar to that of other members of the family Cricetidae and somewhat different from that of other rodents. The central nervous system (CNS) syndrome is similar since the survival time falls from over 100 hours at 15,000 or 20,000 rads to less than 4 hours at 80,000 rads. Similarly, the bone marrow deaths occur within 2 weeks following doses between 840 and 1200 rads. This high minimum lethal value is a characteristic common to certain members of the family Cricetidae, and is exceptional and unique among these radioresistant species. On the other hand, certain inconsistancies were also noted. Animals dying from about 1200 rads to 15,000 or 20,000 rads live for 7 to 10 days after irradiation. This is approximately twice the normal range and it is suggested that it reflects the rate of development of the gastrointestinal (GI) lesion. In additi...

ELECTRON MICROSCOPY OF MITOSIS IN A RADIOSENSITIVE GIANT AMOEBA.

Various aspects of the ultrastructure of the dividing nuclei in the large radiosensitive amoeba Pelomyxa illinoisensis are demonstrated. Evidence of nuclear envelope breakdown is presented, and membrane fragments are traced throughout metaphase to envelope reconstruction in anaphase and telophase. Annuli in the nuclear envelope and its fragments are shown throughout mitosis. During metaphase and anaphase some 15 to 20 mitochondria are aligned at each end of the spindle, and are called polar mitochondria. The radioresistant amoebae Pelomyxa carolinensis and Amoeba proteus do not have polar mitochondria, and Pelomyxa illinoisensis is unique in this regard. The shape of the P. illinoisensis interphase nucleoli differs from that in the two radioresistant species, and certain aspects of nucleolar dissolution in the prophase vary. Helical coils in the interphase nucleoplasm are similar to those in the radioresistant amoebae. A "blister" phase in the flatly shaped telophase nuclei of P. illinoisensis is described which is interpreted to be the result of a rapid nuclear expansion leading to the formation of the normal spherical interphase nuclei.