Role of Fe plaque on arsenic biotransformation by marine macroalgae

Macroalgae can cycle arsenic (As) in the environment. In this study, the role of iron (Fe) plaque manipulation at active sites in the As biotransformation mechanism was investigated. The strain of marine macroalgal species, Pyrophia yezoensis, was inoculated in association with arsenate (As(V)) (1.0 μmol L^-1) and phosphate (10 μmol L^-1) in the medium for 7 days under laboratory-controlled conditions. The Fe plaque was removed by washing the Ti(III)-citrate-EDTA solution before inoculation. The limitation of Fe plaque did not significantly (p > 0.05) affect the chlorophyll fluorescence due to cellular regeneration, which was initiated immediately after washing. However, the speciation and uptake rate of As(V) increased significantly and reduced the inhibitory effect of P on the intracellular uptake of As(V) by P. yezoensis. In the culture medium without Fe plaque, approximately 66% of As(V) was removed with V_max = 0.32 and K_m = 1.92. In the absence of Fe plaque, methylated As species, such as dimethylarsinate (DMAA(V)), was recorded 0.28 μmol L^-1, while in the presence of Fe plaque, the value was 0.16 μmol L^-1. Inorganic trivalent As (As(III)) was absent in the washed samples; however, 0.53 μmol L^-1 concentration of As(III) was still found in the presence of Fe plaque on day 7 of incubation. The results indicated that the absence of Fe plaque promoted higher intracellular uptake of As species, reduced the inhibitory effect of P, mitigated the co-precipitation bond between AsFe plaque and enhanced the detoxification process by DMAA excretion from the cell.