Feed the same bacterium molasses instead of sucrose and you get a different polymer

A team at Hiroshima University fed the bacterium *Bacillus velezensis* AZU-A3 two different carbon sources, refined sucrose and sugarcane molasses, and got out two structurally different exopolysaccharides with measurably different biological activity ^[7][9][4]. For anyone costing a fermentation process, that reframes the feedstock line: the cheap agricultural byproduct is not a substitution to be tolerated but an input that changes the product ^[1][16].

Exopolysaccharides (EPSs) are the sugar polymers bacteria secrete into their surroundings, where they form protective layers and biofilms ^[2]. They are used in pharmaceuticals, medical coatings, surgical sealants and drug delivery systems, chosen for biocompatibility, biodegradability and low toxicity ^[6]. The persistent problem in that market is that the link between polysaccharide structure and biological function is poorly understood, which makes specifying a polymer harder than making one ^[11].

The Hiroshima group characterised the two products using vacuum-ultraviolet circular dichroism spectroscopy at the university's Research Institute for Synchrotron Radiation Science, alongside chromatographic tools ^[8]. Refined sucrose produced a polymer the authors call EPS-S, with an ordered, helical-like molecular conformation ^[9]. Molasses produced EPS-M, glucose-rich and with a more flexible conformation ^[4].

The flexible one performed better in the assays. EPS-M reached 94.23 percent free-radical scavenging activity against 76.43 percent for EPS-S, a gap of 17.8 percentage points ^[10][15]. It also showed significantly stronger antibacterial activity against *Escherichia coli*, *Salmonella enterica* and *Staphylococcus aureus* ^[5]. The researchers attribute the difference in performance to the greater structural flexibility of the molasses-derived polymer ^[4].

"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 the institute and lead author ^[3]. Ibrahim frames the practical use as two-sided: tailoring EPS properties for better antioxidant and antibacterial activity, and doing it with inexpensive substrates such as sugarcane molasses ^[16].

Two cautions before anyone reprices a process. First, the announcement reports no yields, titres, batch sizes or unit costs, and gives no numbers for the antibacterial results, only the direction ^[14]. Molasses is a variable, seasonally inconsistent input; a result showing that composition tracks the carbon source is also a result implying that lot-to-lot variation in the feed will show up in the polymer. Second, the mechanism is not established. The team says its next step is to investigate how different carbon sources regulate EPS biosynthesis, including the metabolic pathways and genes behind the changes in monosaccharide composition, conformation and activity ^[12]. Until that is mapped, this is a correlation between a feedstock and a product spec, useful but not yet controllable.

What to watch: whether the mechanistic follow-up identifies which pathway does the switching, since that is what would turn feedstock choice into a tunable process parameter rather than a two-option menu ^[12]. Also watch for evaluation in more advanced biological models, which Ibrahim says is planned, and for any data on whether EPS-M holds its structure and activity across molasses batches from different mills and seasons ^[12]. The work is published in the Chemical Engineering Journal by Khattab and colleagues ^[13].