Synthesis of intracellular cobalt ferrite nanocrystals by extreme acidophilic archaea Ferroplasma thermophilum

Ferroplasma thermophilum, a sort of extreme acidophilic archaea, which can synthesize intracellular cobalt ferrite nanocrystals, is investigated in this study. The nanocrystals were analyzed with ultrathin sections and transmission electron microscope, with the size of 20–60 nm, the number of more than 30 in each cell at average, which indicated that F. thermophilum can synthesize intracellular nanocrystals and also belongs to high-yield nanocrystals-producing strain. Intriguingly, the nanocrystals contain ferrite and cobalt characterized by EDS X-ray analysis, suggesting that both cobalt and ferrite are potentially contributed to the formation of nanocrystals. Moreover, under the different energy source culture conditions of FeSO4 and CuFeS2, the size and the morphology of the nanocrystals are different. It was also found that the higher initial Fe availability leads to an induced synthesis of larger nanocrystals and the lower oxidation-reduction potential (ORP) leads to an induced effect on the synthesis of nanocrystals with abnormal unhomogeneous size, which suggested that the higher initial Fe availability and the lower oxidation-reduction potential lead to a higher uptake efficiency of iron ions of F. thermophilum by iron and ORP gradient culture.