Abstract
Soluble microbial products (SMPs) are of significant concern in the natural environment and in engineered systems. In this work, poly-γ-glutamic acid (γ-PGA), which is predominantly produced by Bacillus sp., was investigated in terms of pH-induced conformational changes and molecular interactions in aqueous solutions; accordingly, its sedimentation coefficient distribution and viscosity were also elucidated. Experimental results indicate that pH has a significant impact on the structure and molecular interactions of γ-PGA. The conformation of the γ-PGA acid form (γ-PGA-H) is rod-like while that of the γ-PGA sodium form (γ-PGA-Na) is sphere-like. The transformation from α-helix to random coil in the γ-PGA secondary structure is primarily responsible for this shape variation. The intramolecular hydrogen bonds in the γ-PGA-H structure decrease and intramolecular electrostatic repulsion increases as pH increases; however, the sedimentation coefficient distributions of γ-PGA are dependent on intermolecular interactions rather than intramolecular interactions. Concentration has a more substantial effect on intermolecular electrostatic repulsion and chain entanglement at higher pH values. Consequently, the sedimentation coefficient distributions of γ-PGA shift significantly at pH 8.9 from 0.1 to 1.0 g/L, and the viscosity of γ-PGA (5% w/v) significantly increases as pH increases from 2.3 to 6.0.
Highlights
Soluble microbial products (SMPs) secreted by microorganisms in the natural environment and in engineered systems are important and have been extensively studied in the fields of microbiology, geochemistry, biological wastewater treatment and biological fermentation[1,2,3]
The observation that the addition of acid to the medium effectively reduces the viscosity of the culture broth has not been reasonably explained; it has allowed for development of an efficient method to separate and recover γ-PGA from highly viscous culture broth, which minimizes purification and recovery costs for large-scale industrial appliations[29]
Molecular weight, and temperature, conformational changes and molecular interactions may be the primary cause for the significant increase in viscosity as pH increases
Summary
Soluble microbial products (SMPs) secreted by microorganisms in the natural environment and in engineered systems are important and have been extensively studied in the fields of microbiology, geochemistry, biological wastewater treatment and biological fermentation[1,2,3]. They are constituents of natural organic matter, which is ubiquitous in water sources, and is a result of interactions between the hydrologic cycle, biosphere and geosphere[4]. The intramolecular hydrogen bonds are considered the major force for the helical conformation; the conformational changes and molecular interactions, including intramolecular and intermolecular interactions of γ-PGA at different concentrations in aqueous solutions, have not been completely elucidated
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
