Screening of endophytic microorganisms from sweetpotato for the production of antimicrobial compounds

Abstract

This study was an attempt to isolate endophytic microorganism with antimicrobial properties from sweetpotato that are grown in the Philippines. Endophytic microorganisms were isolated from surface-sterilized stem cuttings of selected Philippine sweetpotato varieties such as BSP-SP-17, BSP-SP-22, and NSIC-SP-25. The isolates were purified and tested for antimicrobial activities using spot and streak inoculation methods against Lasiodiplodia theobromae (sweetpotato rot-causing mold), Colletotrichum gleosporioides (yam anthracnose-causing mold), Diploidia natalensis (watermelon and citrus stem end rot-causing mold), and Bacillus subtilis (potato soft rot-causing bacteria). Twenty-one isolates (12 bacteria and 9 fungi) exhibited antimicrobial activities against one or more indicator microorganisms tested. The bacteria were identified through 16S rDNA sequencing analyses as Bacillus megaterium, Bacillus pumilus, Microbacterium arborescens, Micrococcus luteus and Bacillus subtilis. The fungi were also identified through their partial 26S rDNA and ITS region sequencing analyses as Phomopsis sp., Aspergillus sp., Penicillium sp. and two belong to Mycosphaerellaceae and Polyporaceae family respectively. The supernatant of these isolates were further tested against the above four indicator microorganisms and four other types of indicators such as B. subtilis AHU 2035, A. flavus var. asper AHU 7051, Alternaria sp. S-1 and C. albicans CA14. All identified isolates possessed wide spectrum of activity against the indicator microorganisms. B. subtilis, B. megaterium, Penicillum sp. and one isolate belonging to Mycosphaerellaceae family were able to inhibit 6 or more of the indicator microorganisms tested.