Fungus activity promoted transformation of lanthanides during biooxidation ofdivalent manganese
Q. Yu 1, 2), T. Ohnuki 1, 3), K. Tanaka 1), N. Kozai 1), S. Yamasaki 1, 4), F. Sakamoto 1), Y. Tani 5)1) : JAEA 2): China University of Geoscience 3): Tokyo Institute of Technology4): University of Tsukuba 5): University of Shizuoka

Biogeochemical processes in the subsurface influenced theenvironmental mobility of actinides [1]. However, the effect of
their biological response on lanthanides migration has been
unclear. This work compared the transformation of lanthanidesduring biooxidation of Mn(II) by fungus Acremonium strictum
KR21-2 under different incubation conditions. A new Cebinding biomolecule was found to be released from the fungal
cell as an adaptive response of A. strictum to lanthanides [2].
This biomolecule was not found to associate with any othertrivalent lanthanides tested or with Fe. The biomolecule wascharacterized as c.a. 4700 Dalton (Da) in size, and it contains
saccharides.
The Mn(II)-oxidizing fungus A. strictum KR21-2 was used.
The cultivation medium initially contained 0–1 mmol/L Mn(II),0–100 µg/L of each lanthanide element, and 0–100 µL spore
suspension. In some of the experiments, 0.1–0.3 mmol/Ltrisodium citrate was added to the medium to increase thesolubility of the lanthanides in the medium. During incubation,
concentrations of Mn and the 14 lanthanide elements in thesupernatant were monitored by inductively coupled plasma mass
spectrometry (ICP-MS). After 100 h cultivation, the chemical
species of the lanthanides in the liquid phase were analyzed bysize exclusion chromatography coupled with UV–Vis
spectrophotometric and ICP-MS detection (SEC-UV-ICP-MS),and the oxidation states of Ce in the solid phase weredetermined by Ce K-edge X-ray absorption near edge structure(XANES) spectroscopy.
In the absence of citrate, more than 99% of the lanthanides
were removed from the liquid phase at 24 h. After 32 h, Mnoxide was formed, and the sorbed Ce started to be desorbed into
the solution and desorption increased with increasing time (Fig.
1a). From SEC-UV-ICP-MS analysis, a new intense SEC-ICPMS peak for Ce was observed at a retention time of 15.9 min incitrate-free sample (Fig. 1b). This result suggested that thefungal cell may have released a biomolecule with a retention
time of 15.9 min that formed a complex with Ce in solution. The
estimated molecular size of this biomolecule was 4700 Da;
therefore, we refer to this Ce-binding biomolecule as “CB4700”.
Adding citrate decreased the interaction between lanthanides
and fungal cells. As a result, the removed fraction of lanthanides
was less than those in the absence of citrate, and increased withthe formation of Mn oxide. Neither desorption of Ce nor SECUV peak assigned to CB4700 were observed. This result
suggests that CB4700 was released from the fungal cell as an
adaptive response of A. strictum to lanthanides
Fe species were not detected at the retention time whereCB4700 appeared (Fig. 2), indicating that the Ce(IV)-binding
functional group in CB4700 could be different fromsiderophores, a well-known iron carrier which could form
complex with Ce(IV) [3]; Given that electrostatic interaction
between biomolecules and the SEC column affects molecularsize estimation, we used an SEC column with a negative surface
charge (GL-W540, Hitachi High-Technologies Corporation,Tokyo, Japan) and an SEC column with a positive surface

charge (Superdex 200, GE Healthcare Bio-Sciences AB,Uppsala, Sweden). The molecular size of CB4700 estimated by
two columns was similar, suggesting that CB4700 is a neutral
molecule; From XANES analysis, a fraction of Ce in solid
phase was present in the tetravalent state. Considering otherlanthanides (except for Ce) did not bind to CB4700, the XANES
results suggest that CB4700 desorbed Ce(IV) from the solidphase.
To our knowledge, this is the first report of the release of abiomolecule with specific affinity for Ce(IV) as an adaptive
response of fungi to lanthanides. Considering the geochemicalsimilarity between Ce(IV) and tetravalent actinides. It isreasonable to suggest that metabolically active cells have an
important effect on the remobilization of tetravalent actinides,
such as Th(IV), U(IV), and Pu(IV), from nuclear wastematerials to pore water. The findings of this study will be
helpful for understanding lanthanide cycling in the environment,
and for long-term management of nuclear waste sites.

Fig. 1 Changes in (a) lanthanide removal fractions during biooxidationof Mn(II), and (b) SEC-UV-ICP-MS chromatograms of the liquid phasein citrate-free solution after 100 h cultivation.

Fig. 2 The relationships between CB4700 and Fe.

References[1] R. G. Riley and J. M. Zachara, Pacific Northwest Lab.,
Richland, WA, United States (1992).
[2] Q. Yu et al., Geochim. Cosmochim. Ac. 174, 1-12 (2016).
[3] F. J. Millero, Geochim. Cosmochim. Ac. 56, 3123-3132(1992).