Antifungal activity of bacterial isolates from straw mushroom cultivation medium against phytopathogenic fungi

Several bacteria were isolated from straw mushroom (Volvariella volvacea) cultivation medium. There were three potential isolates previously characterized and had a growth inhibition effect against V. volvacea. This screening result leads to further study of the inhibition activity against phytopathogenic fungi. This research aimed to investigate the antifungal activity of three bacterial isolates against three phytopathogenic fungi and identification of the bacteria. The methods used in this study were antifungal assay using co-culture method and disk diffusion assay using the filtrate of each bacteria. The profile of the antifungal compound was identified using ethyl acetate extract followed by evaporation and gas chromatography (GC-MS) analysis. Identification of each isolate was performed using 16S rDNA amplification and sequencing. Three phytopathogenic fungi i.e Cercospora lactucae (InaCC F168), Colletotrichum gloeosporioides (InaCC F304), and Fusarium oxysporum f.sp. cubense (F817) were co-cultured with bacterial isolates C2.2, C3.8, and D3.3. The C3.8 isolate has the highest average inhibition activity either using isolate and filtrate. The result is relatively consistent against three phytopathogenic fungi. The metabolite profile of the C3.8 isolate showed the Bis(2-ethylhexyl) phthalate as the main compound with 97% similarity. Bis(2-ethylhexyl) phthalate had a potential effect as an antibacterial and antifungal compound. According to EzBioCloud and GeneBank databases, the C2.2 isolate was identified as Bacillus tequilensis, C3.8 as Bacillus siamensis, and D3.3 as Bacillus subtilis subsp. subtilis. This study also showed the potential of Bacillus siamensis C3.8 as biocontrol against phytopathogenic fungi.