Feeding Bacteria Molasses Instead of Sugar Boosts Biopolymer's Antibacterial Power

Changing the carbon source used to feed bacteria during fermentation (a process in which microorganisms break down nutrients to grow) can significantly alter the properties of the sugar polymers they produce, known as bacterial exopolysaccharides (EPS). These EPS are secreted by bacteria into their surroundings, where they form protective layers called biofilms (a protective film of microorganisms), and are used in a wide range of medical and industrial applications.

"A simple change in the carbon source dramatically altered the composition, structure and biological activity of the bacterial exopolysaccharides," said Mohamed Ibrahim, a specially appointed associate professor at Hiroshima University's Research Institute for Synchrotron Radiation Science and lead author of the study. Researchers at Hiroshima University compared two carbon substrates — refined sucrose and sugarcane molasses, an inexpensive agricultural byproduct — fed to the bacterium Bacillus velezensis AZU-A3. Using vacuum-ultraviolet circular dichroism spectroscopy at the institute, together with chromatographic tools, the team mapped structural differences between the resulting polymers.

The results, published in the Chemical Engineering Journal, showed that refined sucrose produced a biopolymer called EPS-S, with an ordered, helical-like molecular shape. Sugarcane molasses produced a glucose-rich biopolymer called EPS-M, with a more flexible molecular shape. This flexibility allowed the low-cost molasses-derived polymer to outperform its refined counterpart in biological tests. EPS-M showed 94.23% free-radical scavenging activity (a measure of antioxidant strength), compared with 76.43% for EPS-S, and stronger antibacterial activity against Escherichia coli, Salmonella enterica and Staphylococcus aureus.

Bacterial EPS are widely used in pharmaceuticals, medical coatings, surgical sealants and drug delivery systems because of their biocompatibility, biodegradability and low toxicity.