Antibacterial potential of extracts and metabolites isolated from the endophytic fungus Chaetomium cochliodes against phytopathogenic bacteria

Five fungal endophytes, Alternaria sp., Aspergillus sp., Chaetomium sp., Rhizopus sp. and Curvularia sp., were isolated from an Egyptian herbaceous plant, Tribulus terrestris, and tested for their antibacterial activity against three phytopathogenic bacteria (Pectobacterium carotovorum subsp. carotovorum, Ralstonia solanacearum, Pseudomonas syringae pv. syringae). Chaetomium sp. showed the highest antibacterial activity. This strain was identified morphologically and molecularly as Chaetomium cochliodes MS03 (MW898133) based on the ITS1-5.8S rRNA-ITS2 genomic region. Chaetomium cochliodes caused 15 and 8 mm inhibition zones of P. carotovorum subsp. carotovorum and R. solanacearum, respectively. Chaetomium cochliodes isolate was fermented and extracted with ethyl acetate. The crude extract of C. cochliodes showed strong antibacterial activity against P. carotovorum subsp. carotovorum (inhibition zone = 27 mm). Bioassay guided isolation of the crude extract using silica gel column chromatography was conducted to isolate bioactive secondary metabolites. Minimum inhibitory concentrations (MICs) were 500, 32 and 4 mg/L for C. cochliodes extract, fraction 14 and fraction 15, respectively, against P. carotovorum subsp. carotovorum. Bioactive fractions were analyzed by GC/MS. The bioactive pure compound was identified as 9,12-octadecadienoic acid (Z,Z) and the chemical structure was confirmed by H1 NMR and C13 NMR spectral analysis. The isolated compound showed a promising antibacterial activity against P. carotovorum subsp. carotovorum with MIC value of 32 mg/L.