Lignin solvated in zwitterionic Good’s buffers displays antibacterial synergy against Staphylococcus aureus

What is lignin?

Lignin is a versatile aromatic polymer that forms key structural materials in plants and some algae.  They can be used in a wide range of applications, ranging from fuels to advanced chemicals and materials.  They are particularly important in the formation of cell walls, especially in wood and bark, providing rigidity.  They can further provide a water-impermeable coating to water-conducting xylem vessels and act as a physical barrier against pests and pathogens.   

What is the motivation for the study?

While many of the applications for lignin solvation are industrial and in organic solutions, none are compatible with biological solutions.  Grossman et al explore the ability to solvate lignin in aqueous solutions at biological pH.  This further provides an opportunity to investigate the anti-bacterial effects of lignin against different pathogens offering prospects in the pharmaceutical and biomedical arena.  A Zetasizer Ultra was used to measure the size and zeta potential to further determine the effects different buffers had on lignin stability. 

The Results

Z-average sizes of Pluronics F-127 micelles with and without sugarcane lignin.  F-127 was plotted at concentrations of 1% and 10% (w/v), both of which are above the critical micelle concentration. 

Micelles formed in the presence and absence of lignin.  This indicated that adding lignin to each solution caused the Z-average particle (micelle) size to increase and thus, the lignin as taken up into micelles. 

Z-average particle sizes of sugarcane lignin in 1M NaOH, 3-morpholinopropane-1-sulfonic acid (MOPS), 4-(2-hydroxyethyl)piperazine-1-propanesulfonic acid (EPPS), and 3-(cyclohexylamino)-1-propanesulfonic acid (CAPS).
Table: The solubility and stability of sugarcane lignin in micelle-forming solutions


Grossman et al concluded that particle size, zeta potential along with calculated solubility were used to determine that MOPS, EPPS, and CAPS (MEC) act as chaotropic agents that enable lignin to be solvated in aqueous solutions across a wide range of pH, including biological pH.  They further demonstrate the antibacterial activity of MEC-solvated lignin by adding it to culture medium where it inhibited growth of the bacterial pathogen, S. aureus UAMS-1. 

For more information on this study, please download the paper, “Lignin solvated in zwitterionic Good’s buffers displays antibacterial synergy against Staphylococcus aureus” by Grossman et al here

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