Tapping the biosynthetic potential of marine Bacillus licheniformis LHG166, a prolific sulphated exopolysaccharide producer: structural insights, bio-prospecting its antioxidant, antifungal, antibacterial and anti-biofilm potency as a novel anti-infective lead

Abstract

The escalating global threat of antimicrobial resistance necessitates prospecting uncharted microbial biodiversity for novel therapeutic leads. This study mines the promising chemical richness of <i>Bacillus licheniformis</i> LHG166, a prolific exopolysaccharide (EPSR2-7.22 g/L). It comprised 5 different monosaccharides with 48.11% uronic acid, 17.40% sulfate groups, and 6.09% N-acetyl glucosamine residues. EPSR2 displayed potent antioxidant activity in DPPH and ABTS⁺, TAC and FRAP assays. Of all the fungi tested, the yeast <i>Candida albicans</i> displayed the highest susceptibility and antibiofilm inhibition. The fungi <i>Aspergillus niger</i> and <i>Penicillium glabrum</i> showed moderate EPSR2 susceptibility. In contrast, the fungi <i>Mucor circinelloides</i> and <i>Trichoderma harzianum</i> were resistant. Among G+ve tested bacteria, <i>Enterococcus faecalis</i> was the most susceptible, while <i>Salmonella typhi</i> was the most sensitive to G-ve pathogens. Encouragingly, EPSR2 predominantly demonstrated bactericidal effects against both bacterial classes based on MBC/MIC of either 1 or 2 superior Gentamicin. At 75% of MBC, EPSR2 displayed the highest anti-biofilm activity of 88.30% against <i>B. subtilis</i>, while for G-ve antibiofilm inhibition, At 75% of MBC, EPSR2 displayed the highest anti-biofilm activity of 96.63% against <i>Escherichia coli</i>, Even at the lowest dose of 25% MBC, EPSR2 reduced biofilm formation by 84.13% in <i>E. coli</i>, 61.46% in <i>B. subtilis</i>. The microbial metabolite EPSR2 from <i>Bacillus licheniformis</i> LHG166 shows promise as an eco-friendly natural antibiotic alternative for treating infections and oxidative stress.