The prebiotic effects of hyaluronan (HA) are widely recognized, contributing to improved gut health and immune modulation. Despite its extensive use as dietary supplement, the specific interactions between HA oligosaccharides (o-HAs) and the gut microbiome remain largely unexplored. To investigate its role and metabolic fate in gut homeostasis, 200 mg/day of o-HAs (average molecule weight 1k Da) were added to an automated computer-controlled SIMulator of the Gastrointestinal tract (SIMGI). The results revealed a significant reshaping of the intestinal flora composition by o-HAs, notably reducing the Firmicutes/Bacteroides ratio. Fermentation of o-HAs by gut microbiota significantly increased the abundance of Bifidobacteria, Prevotellaceae_Prevotella, Dialister, Eubacterium, and Sutterella, but decreased that of Catenibacterium, Oscillospira, Klebsiella, and Citrobacter (P < 0.05). This corresponded with significant enhancements in the content of short-chain fatty acids (SCFAs) such as acetic acid, propionic acid and n-butyric acid, highlighting the significant impact of o-HAs at the genus level. Furthermore, analysis of microbial function predicted the downregulation of pathological events in nine human diseases, particularly infectious ones (parasitic and bacterial). Potential inhibitions were observed in metabolic pathways associated with pentose and glucuronate interconversions as well as cationic antimicrobial peptide resistance. These findings underscore the in vitro prebiotic effects of o-HAs and their potential relevance in managing diverticular diseases or preventing metabolic disorders through the regulation of gut microbiota.

Ectoine is a natural macromolecule protector and synthesized by some extremophiles. It provides protections against radiation-mediated oxidative damages and is widely used as a bioactive ingredient in pharmaceutics and cosmetics. To meet its growing commercial demands, we engineered Escherichia coli strains for the high-yield production of ectoine. The ectABC gene cluster from the native ectoine producer Halomonas elongata was introduced into different Escherichia coli (E. Coil) strains via plasmids and 0.8 g L^-1 of ectoine was produced in flask cultures by engineered E. coli BL21 (DE3). Subsequently, we designed the ribosome-binding sites of the gene cluster to fine-tune the expressions of genes ectA, ectB, and ectC, which increased the ectoine yield to 1.6 g L^-1. After further combinatorial overexpression of Corynebacterium glutamicum aspartate kinase mutant (G1A, C932T) and the H. elongate aspartate-semialdehyde dehydrogenase to increase the supply of the precursor, the titer of ectoine reached to 5.5 g L^-1 in flask cultures. Finally, the engineered strain produced 60.7 g L^-1 ectoine in fed-batch cultures with a conversion rate of 0.25 g/g glucose.