Molecular characterization of surfactin biosynthetic gene in Bacillus cereus BT1.8 and its antifungal efficacy against Fusarium oxysporum.

Bacillus sp. is a genus of bacteria that can produce active biosurfactant compounds and has potential as an antimicrobial agent. The Bacillus bacteria used in this study were isolated from the soil of Bekol Baluran National Park, which is predicted to contain various types of bacteria that can inhibit soil-borne pathogenic fungi such as Fusarium oxysporum, considering that this pathogen causes root rot in plants. This study aims to identify the potential of Bacillus spp. isolates BT1.8, BT9.1, and SM2.3 in producing biosurfactants as antifungal agents. The methods used ranged from macroscopic, microscopic, and molecular characterization of bacteria, in-vitro antifungal activity testing using the swab method and creating a F. oxysporum block, to biosurfactant activity testing through hemolytic activity using Blood Agar medium. Molecular analysis of the biosurfactant biosynthesis gene was performed using PCR with specific primers for the srfAD gene. The results showed that the Bacillus sp. BT1.8 isolate exhibited the best antifungal activity with a 69% inhibition zone against the growth of F. oxysporum. Isolate BT1.8 was identified as having 99.11% similarity to B. cereus ATCC1457 and possesses the srfAD gene, which shows a high level of homology with a similar gene in Bacillus halotolerans with accession number WP_105955226.1. Hemolytic activity results also show that all three bacterial isolates can destroy blood cells through beta hemolysis. This indicates that the presence of the surfactin biosynthesis gene can produce biosurfactant compounds that are capable of significantly inhibiting the growth of F. oxysporum. These results show that B. cereus BT1.8 has potential as a biological biocontrol agent in the form of seed coating that can be used in the formulation of environmentally friendly biocidal products.