Microorganisms (Oct 2024)

Isolation, Antibacterial Activity and Molecular Identification of Avocado Rhizosphere Actinobacteria as Potential Biocontrol Agents of <i>Xanthomonas</i> sp.

  • Jesús Rafael Trinidad-Cruz,
  • Gabriel Rincón-Enríquez,
  • Zahaed Evangelista-Martínez,
  • Luis López-Pérez,
  • Evangelina Esmeralda Quiñones-Aguilar

DOI
https://doi.org/10.3390/microorganisms12112199
Journal volume & issue
Vol. 12, no. 11
p. 2199

Abstract

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Actinobacteria, especially the genus Streptomyces, have been shown to be potential biocontrol agents for phytopathogenic bacteria. Bacteria spot disease caused by Xanthomonas spp. may severely affect chili pepper (Capsicum annuum) crops with a subsequent decrease in productivity. Therefore, the objective of the study was to isolate rhizospheric actinobacteria from soil samples treated by physical methods and evaluate the inhibitory activity of the isolates over Xanthomonas. Initially, soil samples collected from avocado tree orchards were treated by dry heat air and microwave irradiation; thereafter, isolation was implemented. Then, antibacterial activity (AA) of isolates was evaluated by the double-layer agar method. Furthermore, the positive/negative effect on AA for selected isolates was evaluated on three culture media (potato-dextrose agar, PDA; yeast malt extract agar, YME; and oat agar, OA). Isolates were identified by 16S rRNA sequence analysis. A total of 198 isolates were obtained; 76 (series BVEZ) correspond to samples treated by dry heat and 122 strains (series BVEZMW) were isolated from samples irradiated with microwaves. A total of 19 dry heat and 25 microwave-irradiated isolates showed AA with inhibition zones (IZ, diameter in mm) ranging from 12.7 to 82.3 mm and from 11.4 to 55.4 mm, respectively. An increment for the AA was registered for isolates cultured on PDA and YME, with an IZ from 21.1 to 80.2 mm and 14.1 to 69.6 mm, respectively. A lower AA was detected when isolates were cultured on OA media (15.0 to 38.1 mm). Based on the 16S rRNA gene sequencing analysis, the actinobacteria belong to the Streptomyces (6) and Amycolatopsis (2) genera. Therefore, the study showed that microwave irradiation is a suitable method to increase the isolation of soil bacteria with AA against Xanthomonas sp. In addition, Streptomyces sp. BVEZ 50 was the isolate with the highest IZ (80.2 mm).

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