Exploration for black-koji mold that can potentially acidify soil

Abstract

The black-koji mold produces a large amount of citric acid during the fermentation process of awamori, a traditional distilled spirit in the Ryukyu islands. Meanwhile, to remove the radioactive cesium from soil in Fukushima by plant, it is suggested that the acidification of the soil is important for releasing the radioactive cesium from soil particle. Our purpose is efficient acidification of the soil using the black-koji mold which is safe for natural environment. We selected 6 strong-acidproducing black-koji strains from the National Research Institute of Brewing collection of Aspergillus luchuensis and A. niger separated from awamori-koji, using the acid-producing ability as an index. Finally, we selected A. luchuensis RIB2503, because the growth ability of the strain at lower temperature could make it possible to endure the winter cold at Fukushima in Tohoku region. The strain indicated the significant and maintained acid-producing ability in solid-state culture growth not only regular temperature but also low temperature. Furthermore, gene expressed analysis of the strain indicated that only the citrate synthase gene transcription of the strain increased with culture time. These results suggest that A. luchuensis RIB2503 strain would be sustainable strain producing the citrate acid and ideal for efficient acidification of the soil, leading to the regeneration of the Fukushima's soil.