Nonribosomal Peptides, Key Biocontrol Components for Pseudomonas fluorescens In5, Isolated from a Greenlandic Suppressive Soil

Abstract

Potatoes are cultivated in southwest Greenland without the use of pesticides and with limited crop rotation. Despite the fact that plant-pathogenic fungi are present, no severe-disease outbreaks have yet been observed. In this report, we document that a potato soil at Inneruulalik in southern Greenland is suppressive against Rhizoctonia solani Ag3 and uncover the suppressive antifungal mechanism of a highly potent biocontrol bacterium, Pseudomonas fluorescens In5, isolated from the suppressive potato soil. A combination of molecular genetics, genomics, and matrix-assisted laser desorption ionization–time of flight (MALDI-TOF) imaging mass spectrometry (IMS) revealed an antifungal genomic island in P. fluorescens In5 encoding two nonribosomal peptides, nunamycin and nunapeptin, which are key components for the biocontrol activity by strain In5 in vitro and in soil microcosm experiments. Furthermore, complex microbial behaviors were highlighted. Whereas nunamycin was demonstrated to inhibit the mycelial growth of R. solani Ag3, but not that of Pythium aphanidermatum, nunapeptin instead inhibited P. aphanidermatum but not R. solani Ag3. Moreover, the synthesis of nunamycin by P. fluorescens In5 was inhibited in the presence of P. aphanidermatum. Further characterization of the two peptides revealed nunamycin to be a monochlorinated 9-amino-acid cyclic lipopeptide with similarity to members of the syringomycin group, whereas nunapeptin was a 22-amino-acid cyclic lipopeptide with similarity to corpeptin and syringopeptin.

Fluorescent Pseudomonas and cyclic lipopeptide diversity in the rhizosphere of cocoyam (Xanthosoma sagittifolium)

“…CLPs produced by Pseudomonas spp. can act as biocontrol agents against several plant pathogens both in in vitro and in vivo conditions (Zachow et al ., ; Raaijmakers et al ., ; Olorunleke et al ., , b; Michelsen et al ., ; Ma et al ., , b).…”

Plant-associated fluorescent <i>Pseudomonas</i> from red lateritic soil: Beneficial characteristics and their impact on lettuce growth

“…This implies the existence of different and independent mechanisms underlying fungal biocontrol by these strains, possibly involving secondary metabolites and/or lytic enzymes as has been described for other Pseudomonas (Compant et al, 2005). Interestingly, recent evidence has pointed to cyclic-lipopeptides as key factors in the biological control of R. solani AG-3 by P. fluorescens (Michelsen et al, 2015).…”

Leveraging ecological theory to guide natural product discovery

“…However, most of the effort to discover the NPs responsible for plant protection have focused on Pseudomonas spp., and several bioactive metabolites have been found [36,52]. For example, non-ribosomal peptides nunamycin and nunapeptin were isolated from Pseudomonas fluorescens in a disease-suppressive potato field in Greenland [64]. The cyclic lipodepsipeptide vicosinamide from Pseudomonas fluorescens DR54 is a potent antifungal agent and biosurfactant [71].…”