Schematic illustration showing how carbon source selection influences the structure and biological properties of exopolysaccharides (EPS) produced by Bacillus velezensis AZU-A3. Sucrose-derived EPS (EPS-S) exhibited a mannose- and uronic acid-rich composition with a more ordered helical-like conformation, whereas sugarcane molasses-derived EPS (EPS-M) showed a glucose-rich composition with a more flexible molecular structure. These substrate-dependent structural differences were associated with enhanced antioxidant and antibacterial activities of EPS-M.
Image Credit: Mohamed I. A. Ibrahim / Hiroshima University
Scientific Frontline: Extended "At a Glance" Summary: Microbial Exopolysaccharide Optimization
The Core Concept: Researchers have discovered that altering the carbon source in bacterial fermentation—specifically using inexpensive sugarcane molasses instead of refined sucrose—can significantly enhance the structural and biological properties of bacterial exopolysaccharides (EPSs).
Key Distinction/Mechanism: By changing the substrate fed to Bacillus velezensis AZU-A3, the resulting biopolymers shift from an ordered, helical-like structure (when fed sucrose) to a more flexible, glucose-rich molecular conformation (when fed molasses), which grants the latter superior antioxidant and antibacterial efficacy.
Major Frameworks/Components:
- Fermentation Modulation: Using varying carbon sources to regulate the monosaccharide composition and molecular conformation of secreted biopolymers.
- Structural Analysis: Employment of vacuum-ultraviolet circular dichroism spectroscopy and chromatographic tools to map polymer variations.
- Biological Activity Testing: Evaluation of antioxidant potential (free-radical scavenging) and antibacterial inhibition against Escherichia coli, Salmonella enterica, and Staphylococcus aureus.
- Sustainable Synthesis: Utilizing agricultural by-products to achieve cost-effective production of high-value biopolymers.
Branch of Science: Microbiology, Biochemistry, Materials Science, and Biomedical Engineering.
Future Application: The development of sustainable, cost-effective, and highly active biomaterials for use in advanced pharmaceuticals, surgical sealants, specialized medical coatings, and targeted drug delivery systems.
Why It Matters: This discovery provides a viable, sustainable path to customizing biopolymer functionality for the biomedical and food industries, effectively turning agricultural waste into high-value medical resources while improving performance over refined alternatives.
Changing the carbon source used during bacterial fermentation—essentially, what bacteria are fed—can 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 Mohamed Ibrahim, a specially appointed associate professor at Hiroshima University’s Research Institute for Synchrotron Radiation Science (HiSOR) and lead author of the study.
Researchers at Hiroshima University compared the effects of two distinct carbon substrates—refined sucrose and sugarcane molasses, an inexpensive agricultural byproduct—on the EPSs produced by the bacterium Bacillus velezensis AZU-A3. Using vacuum-ultraviolet circular dichroism spectroscopy at Hiroshima University's HiSOR, together with chromatographic tools, the team mapped the structural variations among the resulting polymers.
The results, published in the Chemical Engineering Journal in, and 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.”
Published in journal: Chemical Engineering Journal
Authors: Abdelrahman M. Khattab, Mahmoud E. Esmael, Ryota Imaura, Amr A. Nassrallah, Hany A. El-Shemy, Koichi Matsuo, and Mohamed I.A. Ibrahim
Source/Credit: Hiroshima University
Edited by: Scientific Frontline
Reference Number: mcb081926_02