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Dark septate endophytic fungal isolates and their bioremediation potential

Following the 2011 Fukushima nuclear disaster, the environment in Japan, especially in the Fukushima area, was contaminated with radioactive cesium (Cs). This contamination posed a risk to human health, as Cs could accumulate in wild edible mushrooms and organically grown crops, like Chinese cabbage and tomatoes. These crops, known as hyperaccumulators of metal contaminants, were of particular concern.

In the aftermath of this nuclear disaster, 3 Japanese researchers, Ousmane Diene, Nobuo Sakagami and Kazuhiko Narisawa, studied The Role of Dark Septate Endophytic Fungal Isolates in the Accumulation of Cesium by Chinese Cabbage and Tomato Plants under Contaminated Environments.

Symbiotic microorganisms, including mycorrhiza and dark septate endophytic fungi (DSE), are known to associate with various plants. Researchers have been exploring their potential to accumulate heavy metals and Cs. Arbuscular mycorrhizal fungi (AMF), for instance, have been found to accumulate Cs in plants, and they can enhance plant growth and Cs uptake. However, the role of DSEs in managing plant growth and Cs accumulation in contaminated environments has been less studied. DSEs are not common in soil but often form "symbiotic" relationships with plant roots, and they are not very specific in their associations.

These DSEs have been shown to improve plant fitness by aiding in nutrient transfer, nitrogen uptake, and phosphorus uptake. The study aimed to investigate how DSEs interact with Chinese cabbage and tomatoes in Cs-polluted environments, as both are hyperaccumulator vegetables grown in contaminated areas.

The study revealed that DSE fungi could enhance the growth of Chinese cabbage and tomatoes in Cs-contaminated conditions. In some cases, DSEs outperformed AMF in promoting plant biomass. However, this also raised concerns about the potential for increased Cs accumulation in the food chain, which is critical for human health.

Photo credits: Carlos Vegara

The DSEs studied were found to have the ability to decrease Cs accumulation in tomato plants, a novel discovery. This suggests that DSEs may regulate the bioavailability of Cs in polluted environments, showcasing their multifunctional symbiotic relationships with host plants.

While the exact mechanisms behind these interactions remain unclear, it is suggested that Cs might be sequestered in fungal hyphae, or ionizing radiation could play a role. More research is needed to confirm these hypotheses.

Photo credits: Macha

This study highlights the potential of DSE fungi in addressing the issue of food chain contamination by radionuclides, especially in contaminated areas. They could be recommended for tomato growers in such regions, potentially reducing Cs accumulation in the primary food chain. The findings also open doors for further investigations into the mechanisms underlying these beneficial plant-fungus interactions in DSE symbiosis.

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