Discovery of endophytic bacteria with potent antimicrobial activity from Theobroma cacao clone TSH 858 in West Sumatra

Abstract

Abstract Endophytic bacteria are known as a promising source of novel bioactive compounds with antimicrobial potential. Cocoa (Theobroma cacao L.) is a tropical plant that hosts a diverse community of endophytic microorganisms, particularly within its fruit tissue, which is rich in bioactive compounds such as flavonoids and methylxanthines. Despite this potential, information on the biological activities of endophytic bacteria associated with cocoa is still limited. This study aimed to isolate, characterize, molecularly identify, and evaluate the in vitro antimicrobial activity of endophytic bacteria obtained from cocoa fruit tissue. Endophytic bacteria were isolated from mesocarp, mucilage, and surface sterilized seeds using standard dilution and cultivation techniques, yielding a total of 13 morphologically distinct isolates (6 from mesocarp, 4 from seeds, and 3 from mucilage). Macroscopic characterization of the 13 isolates was performed. The 13 isolates were tested for their antimicrobial activity against Staphylococcus aureus using the agar well diffusion method, with zones of inhibition measured in triplicate. Among these isolates, isolate PTSH03 showed the strongest inhibitory activity (27.43 ± 1.00 mm) and was therefore selected for molecular identification through 16S rRNA gene sequencing, which identified it as Bacillus subtilis. These findings indicate that endophytic bacteria from cocoa pods, particularly B. subtilis strain PTSH03, exhibit strong antibacterial activity against S. aureus and are promising candidates for further research as potential sources of novel antimicrobial compounds.