Abstract
Pseudomonas cyclic lipopeptides (CLPs) are encoded non-ribosomally by biosynthetic gene clusters (BGCs) and possess diverse biological activities. In this study, we conducted chemical structure and BGC analyses with antimicrobial activity assays for two CLPs produced by Pseudomonas strains isolated from the cocoyam rhizosphere in Cameroon and Nigeria. LC-MS and NMR analyses showed that the Pseudomonas sp. COR52 and A2W4.9 produce pseudodesmin and viscosinamide, respectively. These CLPs belong to the Viscosin group characterized by a nonapeptidic moiety with a 7-membered macrocycle. Similar to other Viscosin-group CLPs, the initiatory non-ribosomal peptide synthetase (NRPS) gene of the viscosinamide BGC is situated remotely from the other two NRPS genes. In contrast, the pseudodesmin genes are all clustered in a single genomic locus. Nano- to micromolar levels of pseudodesmin and viscosinamide led to the hyphal distortion and/or disintegration of Rhizoctonia solani AG2-2 and Pythium myriotylum CMR1, whereas similar levels of White Line-Inducing Principle (WLIP), another member of the Viscosin group, resulted in complete lysis of both soil-borne phytopathogens. In addition to the identification of the biosynthetic genes of these two CLPs and the demonstration of their interaction with soil-borne pathogens, this study provides further insights regarding evolutionary divergence within the Viscosin group.
Highlights
Pseudomonas cyclic lipopeptides are surface-active metabolites synthesized non-ribosomally by modular multifunctional enzymes named non-ribosomal peptide synthetases (NRPSs) [1]
The soil collection site at Ado-Ekiti, Nigeria, was a cocoyam field located at the Ekiti State University (EKSU) Agricultural Farm while at Umudike, Nigeria, soils were collected from cocoyam experimental plots of the National Root Crops Research Institute (NRCRI)
Our study scrutinizes the biosynthetic machinery of the viscosinamide and pseudodesmin cyclic lipopeptides (CLPs) and how they differ bioinformatically in comparison to other members of the Viscosin group of CLPs
Summary
Pseudomonas cyclic lipopeptides (or CLPs) are surface-active metabolites synthesized non-ribosomally by modular multifunctional enzymes named non-ribosomal peptide synthetases (NRPSs) [1]. CLPs comprise a cyclic oligopeptide lactone ring linked to a fatty acid tail [2]. These molecules mediate multiple biological functions, including biofilm formation, swarming motility, virulence (in plant pathogenic strains), antibacterial, antifungal, anti-oomycete, insecticidal, anti-carcinogenic and antiviral properties [2,3,4,5,6,7]. These bioactive molecules are produced by specific species within the P. syringae complex, P. fluorescens, P. putida and P. asplenii groups [8]. The amino acid residues that line the substrate-binding pocket in the adenylation (A) domain are predictive of the substrates that are incorporated into the growing peptide chain, enabling structural predictions of unknown CLPs [15]
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