Bioactive lipopeptides of ice-nucleating snow bacteriumPseudomonas syringaestrain 31R1

The Diversity of Lipopeptides in the Pseudomonas syringae Complex Parallels Phylogeny and Sheds Light on Structural Diversification during Evolutionary History

Pseudomonas spp. colonize diverse aquatic and terrestrial habitats and produce a wide variety of secondary metabolites, including lipopeptides. However, previous studies have often examined a limited number of lipopeptide-producing strains. In this study, we performed a systematic analysis of lipopeptide production across a wide data set of strains of the Pseudomonas syringae complex (724) by using a combined bioinformatics, mass spectrometry, and phylogenetics approach. The large P. syringae complex, which is composed of 13 phylogroups, is known to produce factins (including syringafactin-like lipopeptides), mycins (including syringomycin-like lipopeptides), and peptins (such as syringopeptins). We found that 80.8% of P. syringae strains produced lipopeptides and that factins were the most frequently produced (by 96% of the producing strains). P. syringae strains were either factin monoproducers or factin, mycin, and peptin coproducers or lipopeptide nonproducers in relation to their phylogenetic group. Our analyses led to the discovery of 42 new lipopeptides, bringing the number of lipopeptides identified in the P. syringae complex to 75. We also highlighted that factins have high structural resemblance and are widely distributed among the P. syringae complex, while mycins and peptins are highly structurally diverse and patchily distributed. IMPORTANCE This study provides an insight into the P. syringae metabolome that emphasizes the high diversity of lipopeptides produced within the P. syringae complex. The production profiles of strains are closely related to their phylogenetic classification, indicating that structural diversification of lipopeptides parallels the phylogeny of this bacterial complex, thereby further illustrating the inherent importance of lipopeptides in the ecology of this group of bacteria throughout its evolutionary history. Furthermore, this overview of P. syringae lipopeptides led us to propose a refined classification that could be extended to the lipopeptides produced by other bacterial groups.

Characterization, Pathogenicity, Phylogeny, and Comparative Genomic Analysis of Pseudomonas tolaasii Strains Isolated from Various Mushrooms in China

Since 2016, devastating bacterial blotch affecting the fruiting bodies of Agaricus bisporus, Cordyceps militaris, Flammulina filiformis, and Pleurotus ostreatus in China has caused severe economic losses. We isolated 102 bacterial strains and characterized them polyphasically. We identified the causal agent as Pseudomonas tolaasii and confirmed the pathogenicity of the strains. A host range test further confirmed the pathogen's ability to infect multiple hosts. This is the first report in China of bacterial blotch in C. militaris caused by P. tolaasii. Whole-genome sequences were generated for three strains: Pt11 (6.48 Mb), Pt51 (6.63 Mb), and Pt53 (6.80 Mb), and pangenome analysis was performed with 13 other publicly accessible P. tolaasii genomes to determine their genetic diversity, virulence, antibiotic resistance, and mobile genetic elements. The pangenome of P. tolaasii is open, and many more gene families are likely to emerge with further genome sequencing. Multilocus sequence analysis using the sequences of four common housekeeping genes (glns, gyrB, rpoB, and rpoD) showed high genetic variability among the P. tolaasii strains, with 115 strains clustered into a monophyletic group. The P. tolaasii strains possess various genes for secretion systems, virulence factors, carbohydrate-active enzymes, toxins, secondary metabolites, and antimicrobial resistance genes that are associated with pathogenesis and adapted to different environments. The myriad of insertion sequences, integrons, prophages, and genome islands encoded in the strains may contribute to genome plasticity, virulence, and antibiotic resistance. These findings advance understanding of the determinants of virulence, which can be targeted for the effective control of bacterial blotch disease.

Lipopeptide families at the interface between pathogenic and beneficial Pseudomonas-plant interactions

Lipopeptides (LPs) are a prominent class of molecules among the steadily growing spectrum of specialized metabolites retrieved from Pseudomonas, in particular soil-dwelling and plant-associated isolates. Among the multiple LP families, pioneering research focussed on phytotoxic and antimicrobial cyclic lipopeptides (CLPs) of the ubiquitous plant pathogen Pseudomonas syringae (syringomycin and syringopeptin). Their non-ribosomal peptide synthetases (NRPSs) are embedded in biosynthetic gene clusters (BGCs) that are tightly co-clustered on a pathogenicity island. Other members of the P. syringae group (Pseudomonas cichorii) and some species of the Pseudomonas asplenii group and Pseudomonas fluorescens complex have adopted these biosynthetic strategies to co-produce their own mycin and peptin variants, in some strains supplemented with an analogue of the P. syringae linear LP (LLP), syringafactin. This capacity is not confined to phytopathogens but also occurs in some biocontrol strains, which indicates that these LP families not solely function as general virulence factors. We address this issue by scrutinizing the structural diversity and bioactivities of LPs from the mycin, peptin, and factin families in a phylogenetic and evolutionary perspective. BGC functional organization (including associated regulatory and transport genes) and NRPS modular architectures in known and candidate LP producers were assessed by genome mining.

Biophysical approaches for exploring lipopeptide-lipid interactions

In recent years, lipopeptides (LPs) have attracted a lot of attention in the pharmaceutical industry due to their broad-spectrum of antimicrobial activity against a variety of pathogens and their unique mode of action. This class of compounds has enormous potential for application as an alternative to conventional antibiotics and for pest control. Understanding how LPs work from a structural and biophysical standpoint through investigating their interaction with cell membranes is crucial for the rational design of these biomolecules. Various analytical techniques have been developed for studying intramolecular interactions with high resolution. However, these tools have been barely exploited in lipopeptide-lipid interactions studies. These biophysical approaches would give precise insight on these interactions. Here, we reviewed these state-of-the-art analytical techniques. Knowledge at this level is indispensable for understanding LPs activity and particularly their potential specificity, which is relevant information for safe application. Additionally, the principle of each analytical technique is presented and the information acquired is discussed. The key challenges, such as the selection of the membrane model are also been briefly reviewed.

Structure, properties, and biological functions of nonribosomal lipopeptides from pseudomonads

Bacteria of the genusPseudomonasdisplay a fascinating metabolic diversity. In this review, we focus our attention on the natural product class of nonribosomal lipopeptides, which help pseudomonads to colonize a wide range of ecological niches.

Gram-negative bacilli-derived peptide antibiotics developed since 2000

Gram-negative bacilli such as Pseudomonas spp., Pseudoalteromonas sp., Angiococcus sp., Archangium sp., Burkholderia spp., Chromobacterium sp., Chondromyces sp., Cystobacter sp., Jahnella sp., Janthinobacterium sp., Lysobacter spp., Paraliomyxa sp., Photobacterium spp., Photorhabdus sp., Pontibacter sp., Ruegeria sp., Serratia sp., Sorangium sp., Sphingomonas sp., and Xenorhabdus spp. produce an enormous array of short peptides of 30 residues or fewer that are potential pharmaceutical drugs and/or biocontrol agents. The need for novel lead antibiotic compounds is urgent due to increasing drug resistance, and this review summarises 150 Gram-negative bacilli-derived compounds reported since 2000, including 40 cyclic lipopeptides from Pseudomonas spp.; nine aromatic peptides; eight glycopeptides; 45 different cyclic lipopeptides; 24 linear lipopeptides; eight thiopeptides; one lasso peptide; ten typical cyclic peptides; and five standard linear peptides. The current and potential therapeutic applications of these peptides, including structures and antituberculotic, anti-cyanobacterial, antifungal, antibacterial, antiviral, insecticidal, and antiprotozoal activities are discussed.

Chemical and biological characterization of sclerosin, an antifungal lipopeptide

Pseudomonas sp. strain DF41 produces a lipopeptide, called sclerosin that inhibits the fungal pathogen Sclerotinia sclerotiorum . The aim of the current study was to deduce the chemical structure of this lipopeptide and further characterize its bioactivity. Mass spectrometry analysis determined the structure of sclerosin to be CH(3)-(CH(2))(6)-CH(OH)-CH(2)-CO-Dhb-Pro-Ala-Leu/Ile-Ala-Val-Val-Dhb-Thr-Val-Leu/Ile-Dhp-Ala-Ala-Ala-Val-Dhb-Dhb-Ala-Dab-Ser-Val-OH, similar to corpeptins A and B of the tolaasin group, differing by only 3 amino acids in the peptide chain. Subjecting sclerosin to various ring opening procedures revealed no new ions, suggesting that this molecule is linear. As such, sclerosin represents a new member of the tolaasin lipopeptide group. Incubation of S. sclerotinia ascospores and sclerotia in the presence of sclerosin inhibited the germination of both cell types. Sclerosin also exhibited antimicrobial activity against Bacillus species. Conversely, this lipopeptide demonstrated no zoosporicidal activity against the oomycete pathogen Phytophthora infestans . Next, we assessed the effect of DF41 and a lipopeptide-deficient mutant on the growth and development of Caenorhabditis elegans larvae. We discovered that sclerosin did not protect DF41 from ingestion by and degradation in the C. elegans digestive tract. However, another metabolite produced by this bacterium appeared to shorten the life-span of the nematode compared to C. elegans growing on Escherichia coli OP50.

PCR detection of novel non-ribosomal peptide synthetase genes in lipopeptide-producing Pseudomonas

Bacterial lipopeptides (LPs) are a diverse group of secondary metabolites synthesized through one or more non-ribosomal peptide synthetases (NRPSs). In certain genera, such as Pseudomonas and Bacillus, these enzyme systems are often involved in synthesizing biosurfactants or antimicrobial compounds. Several different types of LPs have been reported for non-pathogenic plant-associated Pseudomonas. Focusing on this group of bacteria, we devised and validated a PCR method to detect novel LP-synthesizing NRPS genes by targeting their lipoinitiation and tandem thioesterase domains, thus avoiding amplification of genes for non-LP metabolites, such as the pyoverdine siderophores present in all fluorescent Pseudomonas. This approach enabled detection of as yet unknown NRPS genes in strains producing viscosin, viscosinamide, WLIP, or lokisin. Furthermore, it proved valuable to identify novel candidate LP producers among Pseudomonas rhizosphere isolates. By phylogenetic analysis of these amplicons, several of the corresponding NRPS genes can be tentatively assigned to the viscosin, amphisin, or entolysin biosynthetic groups, while some others may represent novel NRPS systems.

Bacterial-based additives for the production of artificial snow: what are the risks to human health?

For around two decades, artificial snow has been used by numerous winter sports resorts to ensure good snow cover at low altitude areas or more generally, to lengthen the skiing season. Biological additives derived from certain bacteria are regularly used to make artificial snow. However, the use of these additives has raised doubts concerning the potential impact on human health and the environment. In this context, the French health authorities have requested the French Agency for Environmental and Occupational Health Safety (Afsset) to assess the health risks resulting from the use of such additives. The health risk assessment was based on a review of the scientific literature, supplemented by professional consultations and expertise. Biological or chemical hazards from additives derived from the ice nucleation active bacterium Pseudomonas syringae were characterised. Potential health hazards to humans were considered in terms of infectious, toxic and allergenic capacities with respect to human populations liable to be exposed and the means of possible exposure. Taking into account these data, a qualitative risk assessment was carried out, according to four exposure scenarios, involving the different populations exposed, and the conditions and routes of exposure. It was concluded that certain health risks can exist for specific categories of professional workers (mainly snowmakers during additive mixing and dilution tank cleaning steps, with risks estimated to be negligible to low if workers comply with safety precautions). P. syringae does not present any pathogenic capacity to humans and that the level of its endotoxins found in artificial snow do not represent a danger beyond that of exposure to P. syringae endotoxins naturally present in snow. However, the risk of possible allergy in some particularly sensitive individuals cannot be excluded. Another important conclusion of this study concerns use of poor microbiological water quality to make artificial snow.