Extracellular polymeric substances dependence of surface interactions of Bacillus subtilis with Cd2+ and Pb2+: An investigation combined with surface plasmon resonance and infrared spectra.

ABSTRACT

Microbial extracellular polymeric substances (EPS) play an important role in resisting the shock load of toxic contaminants to microbial aggregates. In order to investigate the surface interaction process of bacteria with heavy metals, in this work, the kinetics and affinity of heavy metal (CdCl2 and PbCl2) binding on Bacillus subtilis with EPS and without EPS were determined using in situ surface plasmon resonance. The binding mechanism between bacteria (with EPS and without EPS) and heavy metals was probed using Fourier-transform infrared spectra. The effect of heavy metals on aggregations of microbial cells with EPS and without EPS was investigated. The results showed that both the binding of Pb2+ and Cd2+ to bacteria with EPS had a similar kinetics process, however Pb2+ bound to bacterial surface without EPS more firmly compared with Cd2+. From our results we theorized that heavy metals changed the protein secondary structures of bacteria without EPS protection, that EPS reduced the influence of heavy metals on microbial aggregation, and that Pb2+ inhibited cell aggregation more easily compared with Cd2+ in the absence of EPS.