Non-ribosomal Peptide Synthases from Pseudomonas aeruginosa Play a Role in Cyclodipeptide Biosynthesis, Quorum-Sensing Regulation, and Root Development in a Plant Host

Abstract

Diverse molecules mediate cross-kingdom communication between bacteria and their eukaryotic partners and determine pathogenic or symbiotic relationships. N-acyl-L-homoserine lactone-dependent quorum-sensing signaling represses the biosynthesis of bacterial cyclodipeptides (CDPs) that act as auxin signal mimics in the host plant Arabidopsis thaliana. In this work, we performed bioinformatics, biochemical, and plant growth analyses to identify non-ribosomal peptide synthase (NRPS) proteins of Pseudomonas aeruginosa, which are involved in CDP synthesis. A reverse genetics strategy allowed the identification of the genes encoding putative multi-modular-NRPS (MM-NRPS). Mutations in these genes affected the synthesis of the CDPs cyclo(L-Pro-L-Val), cyclo(L-Pro-L-Leu), and cyclo(L-Pro-L-Tyr), while showing wild-type-like levels of virulence factors, such as violacein, elastase, and pyocyanin. When analyzing the bioactivity of purified, naturally produced CDPs, it was found that cyclo(L-Pro-L-Tyr) and cyclo(L-Pro-L-Val) were capable of antagonizing quorum-sensing-LasR (QS-LasR)-dependent signaling in a contrasting manner in the cell-free supernatants of the selected NRPS mutants, which showed QS induction. Using a bacteria-plant interaction system, we further show that the pvdJ, ambB, and pchE P. aeruginosa mutants failed to repress primary root growth, but improved root branching in A. thaliana seedlings. These results indicated that the CDP production in P. aeruginosa depended on the functional MM-NRPS, which influences quorum-sensing of bacteria and plays a role in root architecture remodeling.

Bile Acid 7α-Dehydroxylating Gut Bacteria Secrete Antibiotics that Inhibit Clostridium difficile: Role of Secondary Bile Acids

“…Proline-base cyclic dipeptides are known to be secreted by a number of bacteria (Giessen and Marahiel, 2014) but not members of the genus Clostridium. Proline-based cyclodipeptides have been reported to be quorum-sensing molecules for certain bacteria and to inhibit the growth of both bacteria and fungi (Belin et al, 2012;Gonzá lez et al, 2017). The synthesis and secretion of these molecules by C. difficile raises the possibility that these cyclodipeptides may enhance the ability of this bacterium to colonize the colon following antibiotic treatment by inhibiting the remaining members of the gut microbiota.…”

Earthworms Building Up Soil Microbiota, a Review

“…Since Pseudomonas spp. have frequently been shown to emit SM that may promote plant growth, for instance through an induction of plant resistance to pathogens (Bloemberg and Lugtenberg, 2001;Pieterse et al, 2009;González et al, 2017); the combining next-generation sequencing with state of the art metabolomic tools may help understanding the joint effect of earthworm and PGPB on plant growth.…”

Defining plant growth promoting rhizobacteria molecular and biochemical networks in beneficial plant-microbe interactions

“…Interestingly, the CDPs from P. aeruginosa may have multiple significant functions involved in plant beneficial interactions. Certain CDPs were found to act directly on the LasR AHL QS system to negatively control their own synthesis, which is important as larger concentrations of CDP are required to stimulate lateral root growth as compared to auxin (González et al 2017). The same study used a bioinformatics approach to identify possible non ribosomal peptide synthases responsible for CDP production, and found highly homologous protein sequences associated with the production of the bacterial iron scavenging siderophore pyoverdine.…”