AUTHOR=Qi Dengfeng , Zou Liangping , Zhou Dengbo , Zhang Miaoyi , Wei Yongzan , Zhang Lu , Xie Jianghui , Wang Wei 

TITLE=Identification and Antifungal Mechanism of a Novel Actinobacterium Streptomyces huiliensis sp. nov. Against Fusarium oxysporum f. sp. cubense Tropical Race 4 of Banana

JOURNAL=Frontiers in Microbiology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2021.722661

DOI=10.3389/fmicb.2021.722661

ISSN=1664-302X

ABSTRACT=<p>Banana is an important fruit crop. <italic>Fusarium</italic> wilt caused by <italic>Fusarium oxysporum</italic> f. sp. <italic>cubense</italic> tropical race 4 (Foc TR4) seriously threatens the global banana industry. It is difficult to control the disease spread using chemical measures. In addition, commercial resistant cultivars are also lacking. Biological control is considered as a promising strategy using antagonistic microbes. Actinomycetes, especially <italic>Streptomyces</italic>, are potential sources of producing novel bioactive secondary metabolites. Here, strain SCA2-4<sup><italic>T</italic></sup> with strong antifungal activity against Foc TR4 was isolated from the rhizospheric soil of <italic>Opuntia stricta</italic> in a dry hot valley. The morphological, physiological and chemotaxonomic characteristics of the strain were consistent with the genus <italic>Streptomyces</italic>. Based on the homology alignment and phylogenetic trees of 16S <italic>rRNA</italic> gene, the taxonomic status of strain SCA2-4<sup><italic>T</italic></sup> exhibited a paradoxical result and low bootstrap value using different algorithms in the MEGA software. It prompted us to further discriminate this strain from the closely related species by the multilocus sequence analysis (MLSA) using five house-keeping gene alleles (<italic>atpD</italic>, <italic>gyrB</italic>, <italic>recA</italic>, <italic>rpoB</italic>, and <italic>trpB</italic>). The MLSA trees calculated by three algorithms demonstrated that strain SCA2-4<sup><italic>T</italic></sup> formed a distinct clade with <italic>Streptomyces mobaraensis</italic> NBRC 13819<sup><italic>T</italic></sup>. The MLSA distance was above 0.007 of the species cut-off. Average nucleotide identity (ANI) values between strain SCA2-4<sup><italic>T</italic></sup> genome and two standard strain genomes were below 95-96% of the novel species threshold. Strain SCA2-4<sup><italic>T</italic></sup> was assigned to a novel species of the genus <italic>Streptomyces</italic> and named as <italic>Streptomyces huiliensis</italic> sp. nov. The sequenced complete genome of SCA2-4<sup><italic>T</italic></sup> encoded 51 putative biosynthetic gene clusters of secondary metabolites. Genome alignment revealed that ten gene clusters were involved in the biosynthesis of antimicrobial metabolites. It was supported that strain SCA2-4<sup><italic>T</italic></sup> showed strong antifungal activities against the pathogens of banana fungal diseases. Extracts abstracted from the culture filtrate of strain SCA2-4<sup><italic>T</italic></sup> seriously destroyed cell structure of Foc TR4 and inhibited mycelial growth and spore germination. These results implied that strain SCA2-4<sup><italic>T</italic></sup> could be a promising candidate for biological control of banana <italic>Fusarium</italic> wilt.</p>