Abstract
We present here a quantification of the sorption process and molecular conformation involved in the attachment of bacterial cell wall lipopolysaccharides (LPSs), extracted from Escherichia coli, to silica (SiO2) and alumina (Al2O3) particles. We propose that interfacial forces govern the physicochemical interactions of the bacterial cell wall with minerals in the natural environment, and the molecular conformation of LPS cell wall components depends on both the local charge at the point of binding and hydrogen bonding potential. This has an effect on bacterial adaptation to the host environment through adhesion, growth, function, and ability to form biofilms. Photophysical techniques were used to investigate adsorption of fluorescently labeled LPS onto mineral surfaces as model systems for bacterial attachment. Adsorption of macromolecules in dilute solutions was studied as a function of pH and ionic strength in the presence of alumina and silica via fluorescence, potentiometric, and mass spectrometry techniques. The effect of silica and alumina particles on bacterial growth as a function of pH was also investigated using spectrophotometry. The alumina and silica particles were used to mimic active sites on the surface of clay and soil particles, which serve as a point of attachment of bacteria in natural systems. It was found that LPS had a high adsorption affinity for Al2O3 while adsorbing weakly to SiO2 surfaces. Strong adsorption was observed at low pH for both minerals and varied with both pH and mineral concentration, likely in part due to conformational rearrangement of the LPS macromolecules. Bacterial growth was also enhanced in the presence of the particles at low pH values. This demonstrates that at a molecular level, bacterial cell wall components are able to adapt their conformation, depending on the solution pH, in order to maximize attachment to substrates and guarantee community survival.
Highlights
A lipopolysaccharide (LPS) is an amphiphilic macromolecule with a hydrophobic lipid unit embedded in the outer membrane of Gram-negative bacteria.[1,2] This biologically produced anionic polymer plays an important role in bacterial adhesion,[3] as it is the major component of the outer membrane of Gram-negative bacteria,[4,5] the largest group of culturable cells found in aquatic systems.[6]
Bacteria found in a biofilm matrix are less susceptible to drugs than they are in vitro[15] and this is a known cause of persistence in infections.[16]
For the inductively coupled plasma mass spectrometry analysis (ICP− MS), a PerkinElmer ELAN 400 DRC II was used to determine the amount of unreacted minerals according to the following method: the equilibrated mineral LPS solution was transferred into an ultrafiltration cylinder, and free mineral passed through a filter and collected in a flask
Summary
A lipopolysaccharide (LPS) is an amphiphilic macromolecule with a hydrophobic lipid unit embedded in the outer membrane of Gram-negative bacteria.[1,2] This biologically produced anionic polymer plays an important role in bacterial adhesion,[3] as it is the major component of the outer membrane of Gram-negative bacteria,[4,5] the largest group of culturable cells found in aquatic systems.[6]. AmNS has previously shown to be a reliable reporter of polymer conformation in the solution and has been used to study the adsorption of poly(acrylic acid) onto the surface of calcite.[23] Adsorption of LPS was studied in dilute ionic solutions as a function of pH and in the presence of alumina and silica This approach provides a mechanistic understanding of binding at the interface of the outer cell wall of bacteria and minerals, a process vital to bacterial attachment, growth, and the stability of biofilms. For the inductively coupled plasma mass spectrometry analysis (ICP− MS), a PerkinElmer ELAN 400 DRC II was used to determine the amount of unreacted minerals according to the following method: the equilibrated mineral LPS solution was transferred into an ultrafiltration cylinder (pore size 1 kDa), and free mineral passed through a filter and collected in a flask. Bacterial growth at pH 2 and pH 10, in the presence or absence of particles, was confirmed through plating on TSA
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