Exopolysaccharide (EPS) from marine microalgae are promising sources of a new generation of drugs. However, lot of them remain to be discovered and tested. In this study, EPS produced by Porphyridium marinum and its oligomers prepared by High Pressure Homogenizer have been tested for different biological activities, i.e., antibacterial, anti-fungal and antibiofilm activities on Candida albicans, as well as for their effects on the viability of murine breast cancer cells. Results have shown that all EPS samples present some biological activity. For antibacterial and antibiofilm activities, the native EPS exhibited a better efficiency with Minimum Inhibitory Concentration (MIC) from 62.5 µg/mL to 1000 µg/mL depending on the bacterial strain. For Candida albicans, the biofilm formation was reduced by about 90% by using only a 31.3 µg/mL concentration. Concerning breast cancer cells, lower molar masses fractions appeared to be more efficient, with a reduction of viability of up to 55%. Finally, analyses of polymers composition and viscosity measurements were conducted on all samples, in order to propose hypotheses involving the activities caused by the intrinsic properties of polymers.

As part of the development of alternative and environmentally friendly control against phytopathogenic fungi, Burkholderia cepacia could be a useful species notably via the generation of hydrolytic enzymes like chitinases, which can act as a biological control agent. Here, a Burkholderia contaminans S614 strain exhibiting chitinase activity was isolated from a soil in southern Tunisia. Then, response surface methodology (RSM) with a central composite design (CCD) was used to assess the impact of five factors (colloidal chitin, magnesium sulfate, dipotassium phosphate, yeast extract, and ammonium sulfate) on chitinase activity. B. contaminans strain 614 growing in the optimized medium showed up to a 3-fold higher chitinase activity. This enzyme was identified as beta-N-acetylhexosaminidase (90.1 kDa) based on its peptide sequences, which showed high similarity to those of Burkholderia lata strain 383. Furthermore, this chitinase significantly inhibited the growth of two phytopathogenic fungi: Botrytis cinerea M5 and Phoma medicaginis Ph8. Interestingly, a crude enzyme from strain S614 was effective in reducing P. medicaginis damage on detached leaves of Medicago truncatula. Overall, our data provide strong arguments for the agricultural and biotechnological potential of strain S614 in the context of developing biocontrol approaches.

Potato peel waste (PPW) represents a low-cost and eco-friendly by-product with potential for use as a fermentation substrate for the production of antibacterial metabolites by Bacillus species. This study evaluated PPW as a fermentation matrix for Bacillus velezensis and demonstrated that 2% PPW supported optimal production of antibacterial compounds. The cell-free supernatant obtained after 96 h of fermentation exhibited the strongest activity against E. coli 18/22, with a MIC of 62.5 µg/mL. The ethyl acetate extract exhibited rapid bactericidal activity, killing E. coli 18/22 within 30 min at 2× MIC and within 120 min at MIC. The antibacterial activity remained stable up to 80 °C, across pH 4–12, and after treatment with pepsin and chymotrypsin. LC/HR-ESI-MS analysis identified oxydifficidin and surfactins C14 and C15 as the main active compounds. Molecular docking revealed that oxydifficidin and surfactin C15 exhibited the strongest binding affinity toward Shiga toxin II, while surfactin C14 displayed a weaker interaction, suggesting the role of acyl chain length in toxin binding. Both oxydifficidin and surfactins interacted with key residues within the catalytic pocket of the AcrB subunit of the AcrAB–TolC multidrug efflux pump, indicating potential inhibition of multidrug resistance mechanisms. To our knowledge, this is the first report describing the use of PPW as a fermentation substrate for Bacillus velezensis B38 to produce oxydifficidin and surfactin C14 and C15 exhibiting antimicrobial activity against multidrug-resistant E. coli. These findings provide a promising strategy for transforming agro-industrial waste into value-added antimicrobial metabolites, contributing to the circular bioeconomy strategies within the One Health framework.