Biocontrol of Botrytis cinerea by Streptomyces noursei C27 and preliminary identification of antimicrobial metabolites

A wide variety of soluble bioactive secondary metabolites and volatile organic compounds are produced by species of Streptomyces, making them potential candidates for controlling phytopathogenic microorganisms. In the present study, Streptomyces noursei C27, isolated from soil, was found to exhibit broad spectrum inhibitory activity against several phytopathogenic fungi. Furthermore, volatile organic compounds (VOCs) produced by S. noursei C27 exhibited total inhibition of Botrytis cinerea. An analysis of the complete genome sequence confirmed the identification of C27 as Streptomyces noursei. Liquid chromatography-tandem mass spectrometry analysis was used to characterize antimicrobial metabolites present in the fermentation broth of Streptomyces C27, that were identified as gougerotin, natamycin, nystatin, and anisomycin. Streptomyces C27 was shown to control gray mold on grape leaves and fruit in vitro, inhibiting infections by 72.5% and 71.9%, respectively. Gas chromatography-mass spectrometry analysis revealed that thirty alkenes, alcohols, esters, and alkanes were among the VOCs secreted by Streptomyces C27 and contributed to the inhibition of B. cinerea growth and development in inoculated grape leaves and fruit. The biocontrol efficacy of a wettable powder formulation of Streptomyces C27 against gray mold was tested on tomato seedlings in pot experiments and greenhouse experiment. Results indicated 61.86% and 67.25% control in the pot and field tests, respectively. In summary, Streptomyces noursei C27 has excellent potential to be a commercial biocontrol agent of plant diseases caused by pathogenic fungi, especially gray mold infections of vegetables and fruits caused by B. cinerea.