Streptomyces lydicus M01 Regulates Soil Microbial Community and Alleviates Foliar Disease Caused by Alternaria alternata on Cucumbers

Abstract

Due to the adverse effect on the environment caused by excessive use of chemical fertilizers, the development of sustainable agriculture attracts a growing demand of biological based fertilizers composed of living microorganisms. In this study, an Actinobacteria Streptomyces lydicus M01 was isolated from the rhizosphere soil of Pyrus calleryana. This strain effectively promoted the plant growth and suppressed a foliar disease caused by Alternaria alternata on cucumbers. S. lydicus M01 exhibited growth promoting characteristics such as phosphate solubilization, IAA secretion, siderophore and ACC deaminase production. Through Illumina sequencing of the 16S rRNA gene and ITS gene of the soil microbes, we found that the application of S. lydicus M01 altered the composition of the microbial community by promoting beneficial groups, including bacteria genera Pseudarthrobacter, Sphingomonas, Rhodanobacter, and Pseudomonas, fungi genera Fusicolla, Humicola, Solicoccozyma, and Paraphaeosphaeria. Most of these bacteria and eukaryotes exhibit positive effects on growth promotion, such as nutrient accumulation, auxin secretion, abiotic stress alleviation, biological control, or bioremediation. Furthermore, studies on the reactive oxygen species (ROS) level and antioxidants of cucumber leaves revealed that S. lydicus M01 treatment reduced the ROS accumulation and increased the activities of antioxidases related with ROS scavenging, which indicated an enhanced disease resistance of cucumbers under biotic stress. Thus, our results suggest that the application of S. lydicus M01 can systemically affect plant microbiome interactions and represent a promising sustainable solution to improve agricultural production instead of chemical fertilizers.

Induced Systemic Resistance for Improving Plant Immunity by Beneficial Microbes

“…Bacillus amyloliquefaciens, B. atrophaeus, B. cereus, Pseudomonas fluorescens, etc., were demonstrated to be effective against fungal, bacterial, and viral invasion through ISR (Table 1). Recent studies suggested that beneficial microbes induce early plant ISR events (Table 1), including, but not limited to, increased expression of pathogenesis-related PR genes, enhanced activities of defense-related substances, such as phenylalanine ammonia-lyase, polyphenol oxidase, peroxidase, β-1, 3 glucanase, and chitinase, and accumulating reactive oxygen species [43,44]. PR1, PR2, and PR3 gene (antimicrobial effects, beta-1,3 glucanase, and chitinase activities); enhanced activities of phenylalanine ammonia lyase (regulation of plant growth and stress tolerance), beta-1,3 glucanase (inhibition of the mycelial growth and spore germination), and chitinase (inhibition of mycelial growth).…”

Streptomyces sp. strain TOR3209: a rhizosphere bacterium promoting growth of tomato by affecting the rhizosphere microbial community

“…These strains can change the soil bacterial community and enhancing the disease resistance of plants. Some other studies have shown that PGPR can improve plant resistance and promote plant growth by changing soil microbial community 10,11 .…”

Biocontrol of Soil-Borne Pathogens of Solanum lycopersicum L. and Daucus carota L. by Plant Growth-Promoting Actinomycetes: In Vitro and In Planta Antagonistic Activity

“…The genus Streptomyces is the major producer of antibiotics. It plays an important role in the suppression of plant diseases induced by bacterial pathogens and has a great diversity of genes for the production of biocontrol secondary metabolites [28,29].…”