Molecular mechanism of lipopolysaccharide (LPS) in promoting biomineralization on bacterial surface.

Biomineralization on bacterial surface is affected by biomolecules of bacterial cell surface. Lipopolysaccharide (LPS) is the main and outermost component on the extracellular membrane of Gram-negative bacteria. In the present study, the molecular mechanism of LPS in affecting biomineralization of Ag+/Cl- colloids was investigated by taking advantages of two LPS structural deficient mutants of Escherichia coli. The two mutants were generated by impairing the expression of waaP or wbbH genes with CRISPR/Cas9 technology and it induced deficient polysaccharide chain of O-antigen (ΔwbbH) or phosphate groups of core oligosaccharide (ΔwaaP) in LPS structures. There were significant changes of the cell morphology and surface charge of the two mutants in comparing with that of wild type cells. LPS from ΔwaaP mutant showed increased ΔHITC upon interacting with free Ag+ ions than LPS from wild type cells or ΔwbbH mutant, implying the binding affinity of LPS to Ag+ ions is affected by the phosphate groups in core oligosaccharide. LPS from ΔwbbH mutant showed decreased endotherm (ΔQ) upon interacting with Ag+/Cl- colloids than LPS from wild type or ΔwaaP mutant cells, implying LPS polysaccharide chain structure is critical for stabilizing Ag+/Cl- colloids. Biomineralization of Ag+/Cl- colloids on ΔwbbH mutant cell surface showed distinctive morphology in comparison with that of wild type or ΔwaaP mutant cells, which confirmed the critical role of O-antigen of LPS in biomineralization. The present work provided molecular evidence of the relationship between LPS structure, ions, and ionic colloids in biomineralization on bacterial cell surface.

Lipopolysaccharide-stabilized ionic colloids induce biomineralization.

Biomineralization inducing by bacteria is common in nature. It involves interactions between bacterial surface and metal ions that are usually present in the form of ionic colloids. Lipopolysaccharide (LPS) is the major component of Gram-negative bacterial surfaces. In the present study, interactions between LPS and metal ions (Ag+, Fe3+, Cd2+, Co2+, Cu2+, Mn2+, Ni2+), as well as ionic colloids (Ag+/Cl-, Fe3+/OH-) were evaluated by means of isothermal titration calorimetry and Zeta potential measurement. It was found that LPS increases the energy barrier for the collapse of ionic colloids and prevents ionic colloids from aggregation. The roles of LPS-stabilized ionic colloids in inducing biomineralization on the bacterial surface were explored by means of scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray Diffraction. It showed that reducing colloidal stability by increasing the ionic strength significantly inhibited biomineralization of ionic colloids on bacterial surfaces. While the formation of ionic colloids promoted biomineralization on bacterial surfaces. This study provides a novel insight into biomineralization as well as biomineralization-based techniques with biological stabilizers for producing biominerals.