Biocontrol potential and antifungal mechanism of a novel Streptomyces sichuanensis against Fusarium oxysporum f. sp. cubense tropical race 4 in vitro and in vivo

Most commercial banana cultivars are highly susceptible to Fusarium wilt caused by soilborne fungus Fusarium oxysporum f. sp. cubense (Foc), especially tropical race 4 (TR4). Biological control using antagonistic microorganism has been considered as an alternative method to fungicide. Our previous study showed that Streptomyces sp. SCA3-4( T) had a broad-spectrum antifungal activity from the rhizosphere soil of Opuntia stricta in a dry hot valley. Here, the sequenced genome of strain SCA3-4( T) contained 6614 predicted genes with 72.38% of G + C content. A polymorphic tree was constructed using the multilocus sequence analysis (MLSA) of five house-keeping gene alleles (atpD, gyrB, recA, rpoB, and trpB). Strain SCA3-4( T) formed a distinct clade with Streptomyces mobaraensis NBRC 13819( T) with 71% of bootstrap. Average nucleotide identity (ANI) values between genomes of strain SCA3-4( T) and S. mobaraensis NBRC 13819( T) was 85.83% below 95-96% of the novel species threshold, and named after Streptomyces sichuanensis sp. nov. The type strain is SCA3-4( T) (= GDMCC 4.214( T) = JCM 34964( T)). Genomic analysis revealed that strain SCA3-4( T) contained 36 known biosynthetic gene clusters of secondary metabolites. Antifungal activity of strain SCA3-4( T) was closely associated with the production of siderophore and its extracts induced the apoptosis of Foc TR4 cells. A total of 12 potential antifungal metabolites including terpenoids, esters, acid, macrolides etc. were obtained by the gas chromatography-mass spectrometry (GC-MS). Greenhouse experiment indicated that strain SCA3-4( T) could significantly inhibit infection of Foc TR4 in the roots and corms of banana seedlings and reduce disease index. Therefore, strain SCA3-4( T) is an important microbial resource for exploring novel natural compounds and developing biopesticides to manage Foc TR4.