Characterization of protease-producing bacteria from garden soil and antagonistic activity against pathogenic bacteria

Bacteria play an essential role in various industrial processes, including food, medicine, and detergents, due to their ability to produce protease, a hydrolytic enzyme. This study aimed to identify and characterize protease-producing bacterial strains isolated from garden soil, evaluate their antibiotic susceptibility, and optimize conditions for enhanced protease production. Using skimmed milk agar medium and the gelatin hydrolysis method, 7 bacterial strains (S1, S2, S3, S4, S5, S6, and S7, respectively) were identified for protease production in garden soil. The bacteria were identified based on morphological studies, biochemical characterization, and the BIOLOG™ system, and the isolates were determined to be Bacillus cereus (S1), B. thuringiensis (S2), B. subtilis (S3), B. amyloliquefaciens (S4), Pseudomonas aeruginosa (S5), Macrococcus brunensis (S6), and B. schlegelii (S7). The antibiotic susceptibility test, performed using the Kirby-Bauer agar disc diffusion method, revealed that all isolates were resistant to penicillin, nitrofurantoin, and metronidazole. Additionally, B. subtilis and P. aeruginosa demonstrated antagonistic activity against pathogens. Optimal conditions for protease production were found to be a temperature range of 30°C to 40°C and a pH range of 6.5–7.5. Under these conditions, B. cereus (2.19 U/ml) and B. thuringiensis (2.12 U/ml) exhibited the highest protease activity. Further characterization of protease activity in B. cereus, P. aeruginosa, and M. brunensis under different physiological parameters revealed that maximum activity occurred within a pH range of 5.0–6.0 and temperatures between 30°C and 40°C. Protease activity increased in the presence of calcium (CaCl2) but decreased with the addition of urea. These findings underscore the significant industrial applications of proteases produced by these bacterial strains. [Display omitted] •This study found that B. cereus and B. thuringiensis had the highest protease production under optimal conditions.•All isolates showed resistance to penicillin, nitrofurantoin, and metronidazole in antibiotic susceptibility tests.•Additionally, B. subtilis and Pseudomonas aeruginosa exhibited antagonistic activity against pathogens.•The best conditions for protease production were temperatures of 30°C to 40°C and pH levels of 6.5–7.5.•Protease activity rose with calcium presence but dropped with urea presence.