RESUMEN
Sophorolipids, glycolipid biosurfactants derived from microorganisms such as Starmerella bombicola, possess distinctive surface-active and bioactive properties, holding potential applications in cosmetics, pharmaceuticals and bioremediation. However, the limited structural variability in wild-type sophorolipids restricts their properties and applications. To address this, metabolic engineering efforts have allowed to create a portfolio of molecules. In this study, we went one step further by chemically modifying microbially produced sophorosides, produced by an engineered S. bombicola. Twenty-four new sophoroside derivatives were synthesized, including sophoroside amines with varying alkyl chain lengths (ethyl to octadecyl) on the nitrogen atom and their corresponding quaternary ammonium salts. Additionally, six different microbially produced glycolipid biosurfactants were hydrogenated to achieve fully saturated lipid tails. These derivatives, along with microbially produced glycolipids and three benchmark biosurfactants (di-rhamnolipids, alkyl polyglucosides, cocamidopropyl betaine), were assessed for antimicrobial activity against bacteria (Bacillus subtilis, Staphylococcus aureus, Listeria monocytogenes, Escherichia coli, Pseudomonas aeruginosa) and yeast (Candida albicans). Results indicated that microbially produced glycolipids, such as bola sophorosides, acidic sophorolipids and acidic glucolipids exhibit selective antimicrobial activity against the test organisms. Conversely, lactonic sophorolipids, sophoroside amines and quaternary ammonium salts display a broad antimicrobial activity. N-octyl, N-dodecyl and N-octadecyl derivatives exhibit the lowest minimal inhibitory concentrations, ranging from 0.014 to 20.0 mg mL-1. This study demonstrates the potential synergy of thoughtful biotechnology and targeted chemistry to precisely tailor glycolipid biosurfactants to meet specific requirements across applications.
RESUMEN
Antimicrobial peptides (AMPs) are considered promising candidates to treat various infections in soft tissues and skin. However, no effective treatment based on AMPs has been reached to clinics due to their instability in serum and wounds. Biosurfactants such as acidic sophorolipids (ASLs) of very high concentrations (equal or above 5 mg/mL) have been demonstrated to be antimicrobial agents, however these concentrations might induce cytotoxic effects to human cells. Here, we have demonstrated the synergistic antimicrobial effect of ASL nanoparticles (NPs) and LL37 peptides (below their minimum inhibitory concentrations; MICs) to eradicate Gram-positive and Gram-negative bacteria in human serum (HS) and in the presence of trypsin. The formulations containing ASL NPs (500 µg/mL) and LL37 peptides (15-25 µg/mL) effectively kill wide strains of bacteria in 5 % HS and the presence of trypsin. Moreover, the combination of ASL NPs (500 µg/mL) and LL37 peptides (15 µg/mL) prevents the formation of S. aureus biofilm and eradicates the one-day old biofilm. Importantly, the combination of ASL NPs and LL37 peptides severely damages the cell membrane of Escherichia coli (E. coli) as shown by atomic force microscopy (AFM). The combination of ASL NPs and LL37 peptides rapidly damages the outer (OM) and inner membrane (IM) of E. coli, while ASL NPs (1000 µg/mL) alone slowly compromise the integrity of the bacterial membrane. Importantly, the combination of ASL NPs and LL37 peptides is biocompatible to human keratinocyte cells (HaCaTs) and human umbilical vein endothelial cells (HUVECs), and induces the expression of anti-inflammatory cytokine in macrophages. Overall, ASL NPs in combination with LL37 peptides might be developed as an effective topical formulation to prevent bacterial infections in the skin.
