Marine bacterial activity against phytopathogenic Pseudomonas show high efficiency of Planctomycetes extracts

The genus Pseudomonas integrates several phytopathogenic species like P. syringae pv. syringae (Pss) and P. syringae pv. actinidae (Psa) and P viridiflava. Currently, effective treatments against these Pseudomonas phytopathogens are limited and mostly based on preventive measures or toxic agrochemicals, which pose risks of resistance-acquisition. Marine bacteria may represent new sources of sustainable bioactive compounds with use in agriculture. We assessed the anti-Pseudomonas activity of extracts from marine bacterial strains of seven genera of Actinobacteria and Planctomycetes. Pseudomonas strains were isolated from Portuguese orchards and included five Psa and one Pseudomonas sp. (B65). All the Pseudomonas strains used in this study shared common characteristics regarding swimming-motility, no biofilm-production in abiotic surfaces and production of indole-3-acetic acid (IAA) using a tryptophan-dependent pathway, showing the maintenance of virulence traits in culture. Four representative Pseudomonas strains were exposed to the marine Actinobacteria and Planctomycetes extracts obtained by liquid-liquid phase (LLPE). Only the planctomycetes Alienimonas chondri, Rhodopirellula rubra, Rubrinisphaera brasiliensis and Novipirellula caenicola inhibited Pseudomonas growth with percentages ranging from 56.48% to 83.08%. LC/HRMS dereplication of these bioactive extracts indicated the presence of several bioactive secondary metabolites like diketopiperazines, opening new perspectives for the use of these bacterial isolates and derived compounds in agriculture.

Automated summary

The anti-Pseudomonas activity of extracts from marine bacterial strains was assessed, and four planctomycetes were found to effectively inhibit the growth of Pseudomonas. LC/HRMS dereplication of these extracts revealed the presence of bioactive secondary metabolites, suggesting their potential use in agriculture.