Alkaline‑adapted pectinase from polyextremotolerant Bacillus amyloliquefaciens via agro-wastes valorization: dual biocatalyst and multifunctional bioinoculant.

Alkaline pectinases are pivotal for sustainable industries such as textile scouring, juice clarification, and wastewater treatment; however, strains combining high catalytic activity, true alkalistability, and broad agro-industrial applicability remain scarce. Thirty pectinolytic isolates obtained from decayed fruits in Sidi Bel Abbes, Algeria, yielded three Bacillus amyloliquefaciens strains (SPR6, ST9, SC2) with superior enzyme productivity. Under optimized submerged fermentation (pH 9.0, 37 °C, 48 h), strain ST9 achieved 22.4 U/mL, a 1.78-fold increase over baseline, while replacing commercial pectin with orange peel enhanced yield by 1.32-fold and reduced substrate costs by 99%. The strains exhibited remarkable polyextremotolerance, maintaining viable growth and residual enzymatic activity under abiotic stress conditions (up to pH 12, 50 °C, and 11% NaCl), beyond their optimal production range. Beyond pectinolysis, all isolates co-produced key hydrolases, expressed plant-growth-promoting (PGP) traits (indole-3-acetic acid, siderophores, phosphate solubilization), and suppressed Fusarium and Aspergillus spp. This first report of alkaline-adapted B. amyloliquefaciens producing industrially robust pectinase and exhibiting PGP potential highlights their promise as dual-purpose biocatalysts and bioinoculants for circular-bioeconomy applications.