Nonribosomal Peptides, Key Biocontrol Components for XXXX In5, Isolated from a Greenlandic Suppressive Soil.

@entity11763 @entity415 @entity66
@entity415 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 @entity415 soil at Inneruulalik in southern Greenland is suppressive against Rhizoctonia solani Ag3 and uncover the suppressive antifungal mechanism of a highly potent biocontrol bacterium, @entity11763 In5, isolated from the suppressive @entity415 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 @entity11763 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 @entity11763 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. IMPORTANCE: Crop rotation and systematic pest management are used to only a limited extent in Greenlandic @entity415 farming. Nonetheless, although plant-pathogenic fungi are present in the soil, the farmers do not experience major @entity66 outbreaks. Here, we show that a Greenlandic @entity415 soil is suppressive against Rhizoctonia solani, and we unravel the key biocontrol components for @entity11763 In5, one of the potent biocontrol bacteria isolated from this Greenlandic suppressive soil. Using a combination of molecular genetics, genomics, and microbial imaging mass spectrometry, we show that two cyclic lipopeptides, nunamycin and nunapeptin, are important for the biocontrol activity of @entity11763 In5 both in vitro and in microcosm assays. Furthermore, we demonstrate that the synthesis of nunamycin is repressed by the oomycete Pythium aphanidermatum. Overall, our report provides important insight into interkingdom interference between bacteria and fungi/oomycetes.
