Surface properties of PM2.5 calcite fine particulate matter in the presence of same size bacterial cells and exocellular polymeric substances (EPS) of Bacillus mucitaginosus.

Microorganism cells and spores are the main components of PM2.5 (fine particulate matter) as well as fine mineral particles. In the microscopic system, the microorganisms will affect the minerals through attachment, charge neutralization, and dissolution related to the cell surface structure and metabolite. To explore the process and the results of microbial cells and their extracellular polymeric substances (EPS) acting on the surface properties of minerals of PM2.5 through the metabolism, a common native soil bacterium Bacillus mucitaginosus with abundant extracellular polymers was chosen as the tested strain. Meanwhile, as one of the PM2.5 common minerals, calcite fine particles were taken as the research object to explore the influence of microbial cells and extracellular polymers on its surface properties. High performance liquid chromatography (HPLC), inductively coupled plasma spectrometry (ICP), Zeta potential analysis, Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction spectroscopy (XRD), and scanning electron microscopy (SEM) were used to characterize the composition of EPS, the soluble ions, surface charge, surface groups, crystal form, and surface morphology of calcite residual solid after being treated by the bacterial cells and EPS. The results revealed the EPS of B. mucitaginosus mainly consisted of protein and polysaccharides. Both the whole cell and its EPS could promote the dissolution of calcite particles into calcium ions. Due to the adhesion of organic groups on the calcite surface, the surface potential shifted significantly in the negative direction and the solution pH was clearly increased. The morphology of calcite surface was significantly changed after dissolution and re-crystallization. Experimental results also showed that the existence of the bacteria cells and EPS significantly affected the surface properties of calcite and provide a theoretical basis for the mechanism of PM fine particulate matter on human health impact for further study.