Extracellular polymeric substances (EPS) secreted by Purpureocillium lilacinum strain Y3 promote biosynthesis of jarosite

Abstract

In this study, the biosynthesis of jarosite by Purpureocillium lilacinum was investigated. Firstly, we found when the pH value was lower than 2.50 at 30 °C, the concentration of Fe³⁺ in the solution significantly dropped about 72% after inoculation and a yellow-ocher precipitate was observed on the mycelium surface. X-ray diffraction analysis revealed the precipitate was jarosite. Thereafter, the characterization of the biomineralization process by scanning electron microscopy showed that mineral precipitates started on the cell surface, and then thoroughly covered it. Furthermore the effect of extracellular polymeric substances (EPS) on the biosynthesis of jarosite was investigated. The results suggested Fe³⁺ only dropped 5.2% in 2 days when EPS were stripped. Finally, through monitoring the changes of mycelium surface groups by Fourier transform infrared spectroscopy, we found the biomineralization process originated from the existence of free PO groups in EPS which acted as crystallization nuclei to promote Fe(OH)₃ transformation into jarosite by the formation of P–O–Fe bonds.