Microbial exopolysaccharides (EPS) are extracellular carbohydrate polymers forming capsules or slimy coating around the cells. EPS can be secreted by various bacterial genera that can help bacterial cells in attachment, environmental adaptation, stress tolerance and are an integral part of microbial biofilms. Several gut commensals (e.g., Lactobacillus, Bifidobacterium) produce EPS that possess diverse bioactivities. Bacterial EPS also has extensive commercial applications in the pharmaceutical and food industries. Owing to the structural and functional diversity, genetic and metabolic engineering strategies are currently employed to increase EPS production. Therefore, the current review provides a comprehensive overview of the fundamentals of bacterial exopolysaccharides, including their classification, source, biosynthetic pathways, and functions in the microbial community. The review also provides an overview of the diverse bioactivities of microbial EPS, including immunomodulatory, anti-diabetic, anti-obesity, and anti-cancer properties. Since several gut microbes are EPS producers and gut microbiota helps maintain a functional gut barrier, emphasis has been given to the intestinal-level bioactivities of the gut microbial EPS. Collectively, the review provides a comprehensive overview of microbial bioactive exopolysaccharides.

Trichomoniasis is a neglected, parasitic, sexually transmitted infection. Resistance to the only approved drugs is increasing worldwide, leaving millions of people without alternative medications. Thus, the search for new therapeutic options against this infection is necessary. Previously, our group reported that 1,10-phenanthroline-5,6-dione (phendione) and its silver(I) and copper(II) complexes (abbreviated as Ag-phendione and Cu-phendione, respectively) presented activity against the amitochondriate parasite Trichomonas vaginalis, with Cu-phendione being the most effective (IC50 = 0.84 μM). Methods: qRT-PCR, SEM, flow cytometry. The current study on the effects of Cu-phendione on the antioxidant metabolism of T. vaginalis by qRT-PCR revealed that the complex causes a decrease in the relative expression of mRNA of NADH oxidase, flavin reductase, superoxide dismutase, peroxiredoxin, iron-sulfur flavoprotein, rubrerythrin and osmotically inducible proteins. In contrast, the mRNA expression of flavodiiron protein was increased. Detoxification-related enzymes were downregulated, impairing oxygen metabolism in trophozoites and triggering a subsequent accumulation of the superoxide anion. Although no DNA fragmentation was observed, the treatment of parasites with Cu-phendione led to a significant reduction in cell size and a concomitant increase in granularity. The complex promoted phosphatidylserine exposure at the plasma membrane (as judged by Annexin V binding) and propidium iodide was unable to passively permeate the parasites. All of these outcomes are classical hallmarks of cell death by apoptosis. In essence, the trichomonacidal effect of Cu-phendione operates through redox homeostasis imbalance, which is a mode of action that is quite distinct from that caused by metronidazole.