Characterization of Streptomyces levis L2 with plant disease-inhibiting and growth-promoting effects

Abstract:

[Objective] To study the plant disease-inhibiting and growth-promoting effects and identify the antimicrobial components of Streptomyces levis L2. [Methods] Morphological features and the phylogenetic tree based on the 16S rRNA gene sequences were employed to identify the strain L2 isolated from the rhizosphere of drought-tolerant Echinochloa crusgalli. The antimicrobial components produced by the strain were identified by chromatography and high-resolution mass spectrometry. The whole genome of the strain was sequenced by Illumina in combination with Nanopore. antiSMASH was employed to search for the biosynthetic gene clusters. [Results] Streptomyces levis L2 and its fermentation broth inhibited the growth of Gram-positive bacteria and phytopathogenic fungi, and the strain produced a large transparent zone on the CAS (chrome azurol sulphonate) plate and could produce indole-3-acetic acid (IAA). The antimicrobial components of the strain showed the m/z of 537.102 0 [M+H]⁺ (calcd for C₂₇H₂₀O₁₂, 537.103 5, 2.2×10^–6) and 523.086 3 [M+H]⁺ (calcd for C₂₆H₁₈O₁₂, 523.087 8, 2.9×10^–6), which were consistent with the exact masses of α-rubromycins, β-rubromycins and γ-rubromycins, with the errors less than parts per 5 million. Their HPLC retention time were in agreement with that of standard rubromycins. The whole genome of L2 had a length of 8.8 Mb and carried 32 biosynthetic gene clusters for secondary metabolites including rubromycins. [Conclusion] S. levis L2 exhibited excellent plant disease-inhibiting and growth-promoting properties, thus could be further developed as biocontrol agents. It produces the antimicrobial components rubromycins and its biosynthetic gene clusters contained 6 more modification genes than the previously published gene clusters for rubromycins and several genes with unknown functions.