Τhe Nematicidal Potential of Bioactive Streptomyces Strains Isolated from Greek Rhizosphere Soils Tested on Arabidopsis Plants of Varying Susceptibility to Meloidogyne spp.

Abstract

A total of 461 indigenous Streptomycetes strains recovered from various Greek rhizosphere habitats were tested for their bioactivity. All isolates were examined for their ability to suppress the growth of 12 specific target microorganisms. Twenty-six were found to exert antimicrobial activity and were screened for potential nematicidal action. S. monomycini ATHUBA 220, S. colombiensis ATHUBA 438, S. colombiensis ATHUBA 431, and S. youssoufensis ATHUBA 546 were proved to have a nematicidal effect and thus were further sequenced. Batch culture supernatants and solvent extracts were assessed for paralysis on Meloidogyne javanica and Meloidogyne incognita second-stage juveniles (J2). The solvent extracts of S. monomycini ATHUBA 220 and S. colombiensis ATHUBA 438 had the highest paralysis rates, so these Streptomycetes strains were further on tested for nematodes’ biological cycle arrest on two Arabidopsis thaliana plants; the wild type (Col-0) and the katanin mutant fra2, which is susceptible to M. incognita. Interestingly, S. monomycini ATHUBA 220 and S. colombiensis ATHUBA 438 were able to negatively affect the M. incognita biological cycle in Col-0 and fra2 respectively, and increased growth in Col-0 upon M. incognita infection. However, they were ineffective against M. javanica. Fra2 plants were also proved susceptible to M. javanica infestation, with a reduced growth upon treatments with the Streptomyces strains. The nematicidal action and the plant-growth modulating abilities of the selected Streptomycetes strains are discussed.

Streptomyces, Greek Habitats and Novel Pharmaceuticals: A Promising Challenge

“…However, the majority of compounds, including grecocycline A, grecocycline B, ageloline A, phencomycin, strepoxazine A, strepthonium A, petrocidin A and SKC3, are novel compounds with no other known producers. Greek environments, such as rhizosplere soils, are both rich in streptomycetes and relatively unexplored, making them of great research interest [11]. Actinobacteria, which include Streptomyces, are dominant in arid environments [56], which explains why they are easily isolated from Greek soils.…”

“…The geomorphological and climate conditions prevailing in Greece, including its geographical position and its dry Mediterranean climate, result in soil reservoirs that have a high taxonomic and functional diversity of Streptomyces populations, providing a rich pool of strains with potential pharmaceutical value [9]. In addition to medicine, Greek strains have potential applications in the field of agriculture as biocontrol agents and growth promoters [9][10][11]. Each of these streptomycetes produces multiple secondary metabolites; for example, Streptomyces ambofaciens BI0048, an endophyte isolated from the red alga Laurencia glandulifera from Attiki, produced 10 different α-pyrone polyketides as well as benzoic acid, hydrocinnamic acid and (E)-cinnamic acid [12].…”

Efficiency of Humic Acid and Three Commercial Biocides Against Meloidogyne incognita and Tylenchulus semipenetrans Associated with Olive Plants

“…M. incognita second stages died at a higher rate when Streptomyces hydrogens was used, which resulted in a lower rate of egg hatching (Kaur et al, 2016). Meidani et al, 2020, found that culture supernatants, cell solvent extracts, and spore suspensions of Streptomyces strains from Greece have nematicidal action against M. incognita and M. javanica, as well as negative crop production consequences.…”