Fe, Mn and U accumulations in naturally growing at the mill tailings pond; Iron plaque formation possibly related to root-endophytic bacteria producing siderophores

Nakamoto, Yukihiro*; Doyama, Kohei*; Haruma, Toshikatsu*; Lu, X.*; Tanaka, Kazuya  ; Kozai, Naofumi   ; Fukuyama, Kenjin; Fukushima, Shigeru ; Ohara, Yoshiyuki; Yamaji, Keiko*

Mine drainage is a vital water problem in the mining industry worldwide because of the heavy metal elements and low pH. Rhizofiltration using wetland plants is an appropriate method to remove heavy metals from the water via accumulation in the rhizosphere. is one of the candidate plants for this method because of metal accumulation, forming iron plaque around the roots. At the study site, which was the mill tailings pond in the Ningyo-toge uranium mine, has been naturally growing since 1998. The results showed that accumulated Fe, Mn, and U in the nodal roots without/with iron plaque compared with other plant tissues. Among the 837 bacterial colonies isolated from nodal roots, 88.6% showed siderophore production activities. Considering iron plaque formation around roots, we hypothesized that microbial siderophores might influence iron plaque formation because bacterial siderophores have catechol-like functional groups. The complex of catechol or other phenolics with Fe was precipitated due to the networks between Fe and phenolic derivatives. The experiment using bacterial products of root endophytes, such as spp. and spp., showed precipitation with Fe ions, and we confirmed that several spp. and spp. produced unidentified phenolic compounds. In conclusion, root-endophytic bacteria such as spp. and spp., isolated from metal-accumulating roots of , might influence iron plaque formation as the metal accumulation site. Iron plaque formation is related to tolerance in , and spp. and spp. might indirectly contribute to tolerance.