Isolation and characterization of an Enterococcus strain from Chinese sauerkraut with potential for lead removal

Abstract

Traditional fermented foods are important sources of probiotics, which attract intensive attentions because of their beneficial effects. The potential of probiotic strains to remove heavy metals have also aroused interest from researchers. In this study, the ability of lactic acid bacteria (LAB) isolated from various fermented foods to removal lead (Pb) was tested, and strains with high removal efficiency were selected and characterized by the use of scanning electron microscope equipped with energy dispersive spectrometer (SEM–EDS), Fourier transform infrared spectrometer (FTIR) and X-ray photoelectron spectroscopy (XPS) to investigate the mechanism of lead removal. Two selected strains, identified as Enterococcus faecium DUTYH_16120012 and Enterococcus sp. DUTYH_16120026, were found capable of removing Pb2+ efficiently from MRS broth. Results indicated that initial pH, Pb2+ concentration and growing temperature were important factors affecting lead removal, which might be attributed to the effects of these factors on bacterial growth and physiology. The cell wall played a major role, contributing 80.58 ± 1.65%, in Pb2+ removal by bacterial cells. SEM–EDS and XPS analysis implied that possible chemical compositions of the yellow–brown deposits observed on the cell pellets grown in presence of lead were PbO2 and PbO. FTIR analysis indicated that some functional groups (–OH, –C=O, –N–H, –C–N) were involved in the Pb2+ removal process. The isolated strains demonstrated a potential for lead removal, but further study was needed to reveal the detailed mechanism by which the selected strain removes lead from the growing environment.