Screening, identification and fermentation optimization of an antimicrobial actinomycete strain 17-7 to Phellinus noxius

Abstract:

[Background] Rubber brown root disease, caused by Phellinus noxius Corner, was a disease causing severely damage to rubber trees and huge economic losses in rubber industry. [Objective] To isolate and screen antimicrobial actinomycetes strains with inhibitory activity on Phellinus noxius from the rhizosphere soil of rubber tree. [Methods] The method of dilution plate coating was applied to isolate actinomycetes; The methods of growth plate-confrontation and mycelia growth inhibition were used to screen antimicrobial actinomycetes. Strain 17-7 was identified based on morphological, physiological, biochemical characteristics and 16S rRNA gene sequence. The conditions of fermentation and medium composition were optimized through single factor and orthogonal experiment. [Results] Strain 17-7 showed antimicrobial activity to five plant pathogens of rubber trees. According to the results of morphological, physiological, biochemical characteristics and 16S rRNA gene sequence, strain 17-7 was identified as Streptomyces samsunensi. The optimum culture conditions of strain 17-7 were with a medium of glucose 20.0 g/L, soy powder 25.0 g/L, KH2PO4 1.0 g/L, NaCl 0.5 g/L, CaCO3 0.5 g/L, and liquid volume 150 mL in 500 mL flask, pH 8.0, rotation speed 140 r/min, inoculation amount 10%, culture temperature at 28 °C for 5 d. [Conclusion] Strain 17-7 was identified as Streptomyces samsunensi and showed strongly inhibitory activity against Phellinus noxius.