Surface interaction and biomineralization of uranium induced by the living and dead bacterial ghosts of Kocuria sp.

Abstract

Many researchers investigated that living bacteria could combine with uranium in the water and form bio-minerals. However, the key components and process in promoting the forming of uranium biomineralization are still not very clear. In this study, we investigated the biosorption features and mechanism of living and dead cell wall and cell membrane which including dead bacterial ghosts (D-BGs, Kocuria sp. cells without extracellular polymeric substance-EPS and cytoplasm) and living bacterial ghosts (L-BGs, Kocuria sp. cells without EPS) to interact with U(VI). Macroscopic experiments demonstrated that the maximum capacity of U (VI) by D-BGs up to 82.90%, while the removal ability of L-BGs reduced to 73.03% at pH 6. Added inorganic phosphate could greatly improve the biosorption rate of uranium on cell wall. SEM demonstrated that phosphate could promote amorphous uranium to transform into uranium phosphate (U-P) precipitate in D-BGs. While the lamellar uranium phosphate precipitation was observed on the L-BGs of Kocuria sp. after interacting with uranium. It demonstrated that inactive cell was unable to convert slight precipitations to mineral and L-BGs had ability to form U-P mineralization on the cell surface. Fourier Transform Infrared Spectroscopy (FTIR) results indicated the main functional groups adsorbed U(VI) were PO, C-O, -OH and -COOH. Both X-ray photoelectron spectroscopy (XPS) and FTIR results showed the effect of P element after adsorbing U(VI), indicating phosphate groups is the main biosorption sites for U(VI). Our findings highlight that the necessary inducement of mineralization condition for U(VI) is the metabolic activity of living cells, and adopting analytical pure phosphate to replace secretion of organic, inorganic phosphorus and related enzymes suggested that phosphate is a key regulator of uranium biomineralization.