Mycobiota including Alternaria alternata, Fusarium verticillioides and Aspergillus pulverulents were tested for their ability to uptake radiocobalt (Co-60) and radiocesium (Cs-137) from radionuclid...

Uptake of Radionuclides by Some Fungi

High concentrations of radionuclide contamination of wild mushrooms occurred near the Fukushima Daiichi nuclear power plant and along the path of radioactive plumes. This is a serious problem for the forest ecosystem and commercial wild mushroom production. Radioactivity in wild mushrooms collected from low-level contamination forest areas throughout Japan was measured approximately 6 months after the accident. In general, the radioactivity in mushrooms did not exceed those in the neighboring forest litter. However, further accumulation of 137Cs is expected in mushrooms; therefore, continuous monitoring is necessary even in low-contamination areas. We also found that residual 137Cs radioactivity due to nuclear weapons tests, mainly in 1950s, besides fallout from the Fukushima nuclear accident still remained in soil and was accumulated by mushrooms.

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Mushrooms: Radioactive Contamination of Widespread Mushrooms in Japan

Interest in the interaction of microorganisms with cesium ions (Cs+) has arisen, especially in terms of their potent ability for radiocesium bioaccumulation and their important roles in biogeochemical cycling. Although high concentrations of Cs+ display toxic effects on microorganisms, there have been only limited reports for Cs+-tolerant microorganisms. Here we report enrichment and isolation of Cs+-tolerant microorganisms from soil microbiota. Microbial community analysis revealed that bacteria within the phylum Bacteroidetes, especially Flavobacterium spp., dominated in enrichment cultures in the medium supplemented with 50 or 200 mM Cs+, while Gammaproteobacteria was dominant in the control enrichment cultures (in the presence of 50 and 200 mM K+ instead of Cs+). The dominant Flavobacterium sp. was successfully isolated from the enrichment culture and was closely related to Flavobacterium chungbukense with 99.5% identity. Growth experiments clearly demonstrated that the isolate has significantly higher tolerance to Cs+ compared to its close relatives, suggesting the Cs+-tolerance is a specific trait of this strain, but not a universal trait in the genus Flavobacterium. Measurement of intracellular K+ and Cs+ concentrations of the Cs+-tolerant isolate and its close relatives suggested that the ability to maintain low intracellular Cs+ concentration confers the tolerance against high concentrations of external Cs+.

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Enrichment and isolation of Flavobacterium strains with tolerance to high concentrations of cesium ion

Correlations between potassium, rubidium and cesium (133Cs and 137Cs) in sporocarps of Suillus variegatus in a Swedish boreal forest

The characteristics of Cs accumulation and localization in edible mushrooms were examined using the mycelia of Pleurotus ostreatus-Y1. Scanning electron microscope images revealed the existence of white spots, and energy dispersive X-ray microanalyzer analysis indicated the presence of larger amounts of Cs and P in these spots in mycelia cultured on medium containing 25 mM CsCl. The 137 Cs activities in the mycelia were approximately 4-6 times higher than those in water used for 137 Cs elution. Higher Cs concentrations in the sediment fraction including vacuolar pellets were obtained compared to the upper fractions. It was observed that yellowish spots caused by the fluorescence of 4',6-diamidino-2-phenylindole (DAPI)-stained polyphosphate were localized in the mycelia. The higher fluorescence intensity of the yellowish-grained spots was measured in comparison with other regions in the mycelium. These results suggested that Cs in the mycelia was trapped by polyphosphate in vacuoles or other organelles.

Accumulation and localization of cesium in edible mushroom (Pleurotus ostreatus) mycelia.

Sufficient information on the mechanisms of radiocesium translation from substrate to mushroom and long-term radiocesium accumulation is still not available, though high concentrations of radiocesium were reported in the fruiting bodies of various species of mushrooms especially after the Chernobyl accident. We studied the concentration and existing state of Cs in the cultured mycelium of the edible mushroom (Pleurotus ostreatus (Fr.) Kummer Y-1) using NMR. The133Cs NMR resulting spectra exhibited two resonance signals arising from the mycelium whereas one resonance signal from the external medium and CsCl standard solution. The chemical form of the signal in the downfield found in the only mycelium might be concerned with Cs accumulation in the mycelium.

T. Watanuki

Papers

Studies on uptake of cesium by mycelium of the mushroom ( Pleurotus ostreatus ) by 133 Cs-NMR