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Changing the carbon source used during bacterial fermentation¡ªessentially, what bacteria are fed¡ªcan significantly influence the properties of the sugar polymers they produce, known as bacterial exopolysaccharides (EPSs). 

These EPSs are secreted by bacteria into their surroundings, where they form protective layers or biofilms and serve as valuable materials for 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 , a specially appointed associate professor at ÑÇÉ«ÊÓƵ¡¯s (HiSOR) and lead author of the study.

Researchers at ÑÇÉ«ÊÓƵ compared the effects of two distinct carbon substrates¡ªrefined sucrose and sugarcane molasses, an inexpensive agricultural by-product¡ªon the EPSs produced by the bacterium Bacillus velezensis AZU-A3. Using vacuum-ultraviolet circular dichroism spectroscopy at ÑÇÉ«ÊÓƵ's HiSOR, together with chromatographic tools, the team mapped the structural variations among the resulting polymers.

The results, published in the on June 23, 2026, showed that refined sucrose yielded a biopolymer (EPS-S) characterized by an ordered, helical-like molecular conformation. Conversely, sugarcane molasses produced a glucose-rich biopolymer (EPS-M) with a more flexible molecular conformation.

This greater structural flexibility allowed the low-cost molasses derivative to outperform its refined counterpart in biological tests. The EPS-M demonstrated superior antioxidant capabilities, achieving 94.23% free-radical scavenging activity, compared with 76.43% for EPS-S. It also exhibited significantly stronger antibacterial activity against common pathogenic strains, including Escherichia coli, Salmonella enterica, and Staphylococcus aureus.

Bacterial EPSs are widely used in pharmaceuticals, medical coatings, surgical sealants, and drug delivery systems because of their biocompatibility, biodegradability, and low toxicity. However, understanding the complex relationship between polysaccharide structure and biological function has remained a persistent challenge. ¡°Understanding this relationship enables researchers to tailor EPS properties, improve their antioxidant and antibacterial activities, and develop cost-effective production methods using inexpensive substrates such as sugarcane molasses,¡± Ibrahim said.

These findings offer a sustainable and economically viable approach to customize biopolymers used in the biomedical, pharmaceutical, and food industries.

¡°Our next step is to investigate the molecular mechanisms by which different carbon sources regulate EPS biosynthesis, including the metabolic pathways and genes responsible for changes in monosaccharide composition, molecular conformation, and biological activity,¡± said Ibrahim. 

¡°We also plan to evaluate these EPSs in more advanced biological models and optimize production using sustainable substrates.¡±

The study was conducted by Abdelrahman M. Khattab, Mahmoud E. Esmael, Ryota Imaura, Amr A. Nassrallah, Hany A. El-Shemy, , and Mohamed I.A. Ibrahim, researchers from Al-Azhar University, Cairo University, the Egypt-Japan University of Science and Technology, the National Institute of Oceanography and Fisheries, and ÑÇÉ«ÊÓƵ. Matsuo is a researcher at the , the , and the Research Institute for Synchrotron Radiation Science at ÑÇÉ«ÊÓƵ, where Ibrahim also serves as a specially appointed associate professor.

• Journal: Chemical Engineering Journal
• Title: Carbon source modulates composition, conformation, and activity of exopolysaccharides from Bacillus velezensis AZU-A3
• Authors: Abdelrahman M. Khattab, Mahmoud E. Esmael, Ryota Imaura, Amr A. Nassrallah, Hany A. El-Shemy, Koichi Matsuo & Mohamed I.A. Ibrahim
• DOI: