Isolation and Characterization of New 16-Membered Macrolides from the aveA3 Gene Replacement Mutant Strain Streptomyces avermitilis TM24 with Acaricidal and Nematicidal Activities

Biotechnological potential of actinomycetes in the 21st century: a brief review

This brief review aims to draw attention to the biotechnological potential of actinomycetes. Their main uses as sources of antibiotics and in agriculture would be enough not to neglect them; however, as we will see, their biotechnological application is much broader. Far from intending to exhaust this issue, we present a short survey of the research involving actinomycetes and their applications published in the last 23 years. We highlight a perspective for the discovery of new active ingredients or new applications for the known metabolites of these microorganisms that, for approximately 80 years, since the discovery of streptomycin, have been the main source of antibiotics. Based on the collected data, we organize the text to show how the cosmopolitanism of actinomycetes and the evolutionary biotic and abiotic ecological relationships of actinomycetes translate into the expression of metabolites in the environment and the richness of biosynthetic gene clusters, many of which remain silenced in traditional laboratory cultures. We also present the main strategies used in the twenty-first century to promote the expression of these silenced genes and obtain new secondary metabolites from known or new strains. Many of these metabolites have biological activities relevant to medicine, agriculture, and biotechnology industries, including candidates for new drugs or drug models against infectious and non-infectious diseases. Below, we present significant examples of the antimicrobial spectrum of actinomycetes, which is the most commonly investigated and best known, as well as their non-antimicrobial spectrum, which is becoming better known and increasingly explored.

Natural nematicidal metabolites and advances in their biocontrol capacity on plant parasitic nematodes

Covering: 2010 to 2021Natural nematicidal metabolites are important sources of nematode control. This review covers the isolation and structural determination of nematicidal metabolites from 2010 to 2021. We summarise chemical structures, bioactivity, metabolic regulation and biosynthesis of potential nematocides, and structure-activity relationship and application potentiality of natural metabolites in plant parasitic nematodes' biocontrol. In doing so, we aim to provide a comprehensive overview of the potential roles that natural metabolites can play in anti-nematode strategies.

Acyltransferase Domain Swapping for the Production of Tenvermectin B Metabolites in Genetically Engineered Strain Streptomyces avermitilis HU02

Tenvermectins A and B (TVMs A and B) are hybrid natural compounds of avermectins and milbemycins with enhanced insecticidal activity. Aiming at obtaining a strain for the production of the higher activity metabolite-TVM-B as a major constituent, a recombinant strain Streptomyces avermitilis HU02 was constructed by a domain swapping strategy in which milA1-AT0 gene in S. avermitilis MHJ1011 was replaced by eryA1-AT0 gene from Saccharopolyspora erythraea ATCC 40137. Chemical investigation on the culture of S. avermitilis HU02 led to the isolation of a large amount of TVM-B and trace amounts of five new TVM-B analogues. The structures of new metabolites were elucidated by extensive spectroscopic analysis including 1D and 2D nuclear magnetic resonance and high-resolution electrospray ionization mass spectrometry data. The bioassay test indicated that five new TVM-B analogues exhibited potent insecticidal activity against Tetranychus cinnabarinus and Bursaphelenchus xylophilus. This study provided a feasible route to the low-cost production of TVM-B and enriched the structural diversity of TVM-B metabolites.

Characterization of Nematicidal Activity and Nematode-Toxic Metabolites of a Soilborne Brevundimonas bullata Isolate

The increasing prevalence of crop-threatening root-knot nematodes (RKNs) has stimulated extensive research to discover effective nematicides. A highly focused strategy for accomplishing this is the development of biocontrol agents by a variety of soilborne microorganisms, as different bacterial metabolites have demonstrated promising nematicidal activities. In this study, we characterized the nematicidal and suppressive activity of a bacterial isolate against the agriculturally important RKN Meloidogyne incognita and the model nematode Caenorhabditis elegans, and the main M. incognita-toxic metabolite of the strain. After a preliminary screening of 22 bacterial isolates with a corrected mortality (CM) of whole-cell culture greater than 50% against C. elegans from different RKN-incident soils in China, a total of 14 isolates with CM of the supernatant of culture suspension (SCS) higher than 50% against both M. incognita and C. elegans were rescreened. An isolate with the highest CM of 86.1% and 95.0% for M. incognita and C. elegans, respectively, was further identified as the species Brevundimonas bullata via morphological examination, physiological and biochemical assays and alignment analysis of 16S rRNA gene sequences. The SCS of this strain, namely, B. bullata MB756, exhibited synchronous M. incognita killing activity along with significant detrimental effects on the growth, brood size, and locomotion of C. elegans. The effects of heat treatment, pH, inoculations, and protease K proteolysis on the CM of MB756 SCS were evaluated. A major M. incognita-toxic substance in the MB756 SCS was assayed and identified using thin-layer chromatography, column chromatography and high-performance liquid chromatography with a mass spectrometer, and it was preliminarily identified as 2-ethylhexan-1-ol, with a molecular formula of C₈H₁₈O and a molecular weight of 130.3 Da.

High Value Utilization of an Avermectin Fermentation Byproduct: Novel B2a Derivatives as Pesticide Candidates

In an effort to develop novel molecules with suitable insecticidal activities, 23,24-alkene-avermectin B2a derivatives have been synthesized via a one-pot multistep reaction using avermectin B2a, a byproduct of avermectin fermentation, as a starting material. All products and intermediates were characterized by ¹H NMR, ¹³C NMR, and high-resolution mass spectrometry. Bioassay results showed that the LC₅₀ values of compounds 4 and 9 against Meloidogyne incognita were 0.63 and 0.50 mg/L, respectively, similar to that of avermectin (0.46 mg/L). Importantly, the LC₅₀ values of compound 9 against Tetranychus cinnabarinus and Mythimna separate were 0.0067 and 0.047 mg/L, respectively, superior to that of avermectin. Through field experiments, it could be found that spraying 0.25% water-dispersible granules of compound 9 345 g ha^-1 could effectively control M. incognita outbreaks, with an efficacy of 84.9%. Combined with toxicity experiments, it could be further inferred that compound 9 may be useful as a low-toxicity pesticide. In summary, we efficiently synthesized a new B2a derivative as a potential pesticide and offered an important way for improving the utilization efficiency of avermectin fermentation products. In doing so, the environmental pollution associated with fermentation byproducts may be greatly reduced, potentially enabling a sustainable avermectin fermentation process.

Two new 13-hydroxylated milbemycin metabolites from the genetically engineered strain Streptomyces avermitilis AVE-H39

Two new milbemycin metabolites, 13α-hydroxymilbemycin β₁₃ (1) and 26-methyl-13α-hydroxymilbemycin β₁₃ (2), were isolated from the fermentation broth of a genetically engineered strain Streptomyces avermitilis AVE-H39. Their structures were determined by the comprehensive spectroscopic data, including 1 D, 2 D NMR, MS spectral analysis and the comparison with data from the literature. Compounds 1 and 2 not only exhibited potent acaricidal activities against Tetranychus cinnabarinus, but also had nematocidal activity against Bursaphelenchus xylophilus.

Two novel milbemycin derivatives from the genetically engineered strain Streptomyces avermitilis AVE-H39

Two novel milbemycin derivatives, 5,27-epoxy-13α-hydroxy milbemycin β₁₁ (1) and 5,27-epoxy-13α-hydroxy-25-ethyl milbemycin β₁₁ (2), were isolated from the genetically engineered strain Streptomyces avermitilis AVE-H39. Their structures were elucidated through the interpretation of HR-ESIMS and extensive NMR spectroscopic data. Compounds 1 and 2 exhibited moderate acaricidal and nematicidal activities.