Geobacillus is a thermophilic bacterium known for its ability to produce various metabolites, including thermostable enzymes, chemical compounds, and antimicrobial peptides, particularly bacteriocins. This study aimed to assess the antibacterial potential of Geobacillus subterraneus Tm6Sp1, isolated from the crater of Mount Kamojang in Indonesia, as a novel approach for combating pathogenic bacteria. The utilization of cell immobilization techniques provided an environment conducive to antibacterial substance production and facilitated higher cell density for enhanced communication. Antibacterial preparations were carried out by cultivating G. subterraneus in Mueller- Hinton Broth supplemented with CaCl2 and MgSO4 for 18 h. The antibacterial activity of free and immobilized cells was evaluated at 55°C, with culture broth collected at 18-h intervals for up to four repeated batch fermentations. The resulting G. subterraneus filtrates were then tested for their antibacterial activity against pathogenic bacteria. The findings revealed that the maximum antibacterial activity was observed in the first batch of free cells, exhibiting inhibition zones of 6.90 mm, 10.05 mm, and 16.54 mm against Staphylococcus aureus, Salmonella enteritica, and Escherichia coli, respectively. Conversely, immobilized cells in the fourth batch demonstrated higher inhibition zones of 8.54 mm, 19.75 mm, and 18.04 mm against S. aureus, S. enteritica, and E. coli, respectively. In conclusion, immobilized cells of G. subterraneus exhibited optimal antibacterial substance production in the fourth batch of fermentation, showing antagonistic activity against several pathogenic bacteria.
Key words: antibacterial activity, cell immobilization, Geobacillus subterraneus Tm6Sp1, optimum batch
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