Abstract
Pseudomonas species are metabolically robust, with capacity to produce secondary metabolites including cyclic lipopeptides (CLPs). Herein we conducted a chemical analysis of a crude CLP extract from the cocoyam rhizosphere-derived biocontrol strain Pseudomonas sp. COW3. We performed in silico analyses on its whole genome, and conducted in vitro antagonistic assay using the strain and purified CLPs. Via LC-MS and NMR, we elucidated the structures of four novel members of the bananamide group, named bananamides D-G. Besides variability in fatty acid length, bananamides D-G differ from previously described bananamides A-C and MD-0066 by the presence of a serine and aspartic acid at position 6 and 2, respectively. In addition, bananamide G has valine instead of isoleucine at position 8. Kendrick mass defect (KMD) allowed the assignment of molecular formulae to bananamides D and E. We unraveled a non-ribosomal peptide synthetase cluster banA, banB and banC which encodes the novel bananamide derivatives. Furthermore, COW3 displayed antagonistic activity and mycophagy against Pythium myriotylum, while it mainly showed mycophagy on Pyricularia oryzae. Purified bananamides D-G inhibited the growth of P. myriotylum and P. oryzae and caused hyphal distortion. Our study shows the complementarity of chemical analyses and genome mining in the discovery and elucidation of novel CLPs. In addition, structurally diverse bananamides differ in their antimicrobial activity.
Highlights
Fluorescent Pseudomonas species possess a robust metabolic machinery with the inherent ability to produce multiple and diverse secondary metabolites, including antibiotics, rhamnolipids and cyclicMolecules 2019, 24, 4170; doi:10.3390/molecules24224170 www.mdpi.com/journal/moleculesMolecules 2019, 24, 4170 lipopeptides (CLPs) [1,2]
The molecular formula of produced compounds can be deduced from the m/z (z = 1) using an approach that combines regular Kendrick mass defect calculations with knowledge stored in the NORINE
The m/z of a compound is represented as coordinates in the regular Kendrick mass defect (RKMD)/nominal Kendrick mass (NKM) 2D-plot and the corresponding molecular formula can be deduced [37]
Summary
Fluorescent Pseudomonas species possess a robust metabolic machinery with the inherent ability to produce multiple and diverse secondary metabolites, including antibiotics, rhamnolipids and cyclicMolecules 2019, 24, 4170; doi:10.3390/molecules24224170 www.mdpi.com/journal/moleculesMolecules 2019, 24, 4170 lipopeptides (CLPs) [1,2]. CLPs are bioactive molecules which possess multiple functions in the producing bacteria, including swarming motility, biofilm formation, virulence, and can further mediate biological control against plant pathogens via direct antagonism and elicitation of induced systemic resistance (ISR) [3,4,5,6,7]. CLP members belonging to these families have been described from Pseudomonas strains isolated from diverse ecologies [11]. These molecules are encoded by non-ribosomal peptide synthetases (NRPSs) via distinct modules which comprise adenylation (A), condensation (C) and thiolation (T) domains [12,13,14,15]
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