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. 2023 Oct 18;12(20):3612.
doi: 10.3390/plants12203612.

Albocycline Is the Main Bioactive Antifungal Compound Produced by Streptomyces sp. OR6 against Verticillium dahliae

Carla Calvo-Peña  1 , Rebeca Cobos  1 , José María Sánchez-López  2 , Ana Ibañez  1 , Juan José R Coque  1
Affiliations

Albocycline Is the Main Bioactive Antifungal Compound Produced by Streptomyces sp. OR6 against Verticillium dahliae

Carla Calvo-Peña et al. Plants (Basel). .

Abstract

Verticillium wilt is a soil-borne fungal disease that affects olive trees (Olea europaea) and poses a serious threat to their cultivation. The causal agent of this disease is Verticillium dahliae, a pathogen that is difficult to control with conventional methods. Therefore, there is a need to explore alternative strategies for the management of Verticillium wilt. In this study, we aimed to isolate and characterize actinobacteria from the rhizosphere of olive trees that could act as potential biocontrol agents against V. dahliae. We selected a Streptomyces sp. OR6 strain based on its in vitro antifungal activity and its ability to suppress the pathogen growth in soil samples. We identified the main active compound produced by this strain as albocycline, a macrolide polyketide with known antibacterial properties and some antifungal activity. Albocycline was able to efficiently suppress the germination of conidiospores. To our knowledge, this is the first report of albocycline as an effective agent against V. dahliae. Our results suggest that Streptomyces sp. OR6, or other albocycline-producing strains, could be used as a promising tool for the biological control of Verticillium wilt.

Keywords: Verticillium dahliae; Verticillium wilt; albocycline; antifungal; biocontrol; olive.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Antifungal activity of the 6 best rhizosphere isolates against the fungal phytopathogen V. dahliae V937I as detected by a bioassay-based in vitro screening (A); inhibition index of the 6 best isolates (B).
Figure 2
Figure 2
Partial details of the Neighbor-Joining tree generated from the MLSA analysis showing the location of the selected strains Streptomyces sp. OR14, OR92, OR6 (A), Streptomyces sp. OR58 (B), Streptomyces sp. OR67 (C), and Streptomyces sp. OR96 (D). See Supplementary Materials, Figure S1 for the complete tree.
Figure 3
Figure 3
Analysis of cross interactions between the four different selected rhizosphere Streptomyces sp. strains after MLSA analysis. In this case, strain OR6 was acting as “tester strain” and strains OR58, OR67, and OR96 were acting as “receiver strains”. Each strain was challenged with each other on a Petri dish co-culture bioassay 3 times (n = 9). Similar assays were carried out using strains OR58, OR67, and OR96 as receivers.
Figure 4
Figure 4
Small-scale in vitro soil assay to test the antifungal activity of the selected strains OR6, OR58, OR67, and OR96 against V. dahliae. * No viable V. dahliae was detected at 14 days (d) of the experiment. ** An average of 25 ± 3 Colony Forming Units (cfu) of V. dahliae per g of soil were detected at 14 d of the experiment. The values shown are the mean of two independent experiments performed in triplicate.
Figure 5
Figure 5
Analysis of antifungal activity against V.dahliae in the 12 fractions obtained by vacuum flash chromatography (VFC) during the fractionation of a crude extract (fermentation broth) obtained from a liquid culture of Streptomyces sp. OR6. Note that most of the total antifungal activity is concentrated in fractions 4 and 5–6.
Figure 6
Figure 6
Structural elucidation of albocycline as the main antifungal compound produced by isolate OR6. (A) Chemical structure with carbon positions labeled; (B) 13C, 1H, and Heteronuclear Multiple Bond Connectivity (gHMBC) NMR spectral data of albocycline (δ (ppm), JHH (Hz); CDCl3).
Figure 7
Figure 7
Probit analysis for germination of conidiospores of V. dahliae V937I strain after treatment with albocycline. The data represented are the average of 3 independent experiments made by duplicate.
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