Isolation of yeast endophytes from healthy seeds of Capsicum annuum L. and assessment of their antimicrobial activity

Abstract

Endophytic fungi have been frequently detected in various plant species, but an understanding of the characteristics and biological properties of endophytic fungi of Capsicum annuum L. seeds has not yet been carried out. The present work was designed to isolate the endophytic fungi associated with the seeds of C. annuum L. and a preliminary assessment of the antimicrobial activity of the crude metabolites produced by the isolated endophytes against some human test pathogens. The healthy seeds, after surface sterilization, were inoculated on different growth mediums, namely Potato Dextrose Agar (PDA), Host Extract + Agar (HEA), and Water Agar (WA) under aseptic conditions and incubated at 24±1°C for several days. The result indicated that the seeds were colonized by several yeast endophytes. The maximum number of yeast endophytes was isolated from the PDA medium (32), followed by HEA (8) and WA medium (0), and the endophytes formed six distinct colonies (CA1-CA6). Antimicrobial activity assay of the crude metabolites of the yeast isolates cultured on Potato Dextrose Broth (PDB) revealed that yeast isolates CA5 had higher antimicrobial activity than isolate CA1 against all human pathogens. In addition, crude metabolites of a yeast isolate CA1 showed antimicrobial activity against MTCC 736 (Bacillus subtilis) (when cultured on 50% PDB) and MTCC 737 (Staphylococcus aureus) (when cultured on 12.5% and 25% PDB). Furthermore, antimicrobial activity of the crude metabolites of yeast isolates CA5 was observed against MTCC 736 (B. subtilis) (highest when cultured on 25% PDB) and MTCC 424 (Pseudomonas aeruginosa) (highest when cultured on 12.5% and 25% PDB). In comparison, isolate CA5 showed the highest antimicrobial activity against all the tested human pathogens than isolate CA1.