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An Integrative Approach for the Characterization of Plant-Pathogenic Streptomyces spp. Strains Based on Metabolomic, Bioactivity, and Phylogenetic Analysis.

ABSTRACT: Actinomycetes are generally recognized as a diverse group of gram-positive, mycelium-forming, soil bacteria that play an important role in mineralization processes and plant health, being Streptomyces the most well-known genus from this group. Although plant pathogenicity is a rare attribute in this genus, some species have significant impact worldwide due to their ability to cause important crop diseases such as potato common scab (CS). In this work, an integrative approach was applied to investigate the pathogenic potential of Streptomyces spp. isolates obtained from a local collection of actinomycetes isolated from potato fields. Secretion of phytotoxic compounds was verified in most pathogenic strains from our collection (27 out of 29), and we followed metabolomic analysis to investigate those phytotoxins. We first evaluated the production of the known phytotoxins thaxtomin A (TXT) and desmethylmensacarcin (DMSN) in phytotoxic Streptomyces spp. by HPLC analysis, resulting in 17 TXT and 6 DMSN producers. In addition, NMR-based metabolomic models were able to classify strains according to their phytotoxicity, and metabolomic data was also used to infer chemotaxonomy within pathogenic species. A correlation between phylogeny and the production of distinct phytotoxins was found, supporting the idea that there are "species specific" metabolites produced by this genus. The recently discovered polyketide DMSN was associated unequivocally with S. niveiscabiei strains and was not produced by other species in the growth conditions employed. Two S. niveiscabiei and two S. puniciscabiei phytotoxic strains that did not produce TXT nor DMSN suggest the production of other kind of metabolites involved in phytotoxicity, and allowed the prioritization of these strains for further chemical studies. Indeed, we found two S. niveiscabiei strains whose supernatants were not phytotoxic in the radish assay, suggesting other pathogenic mechanisms involved. We believe our work will be useful to help understand relations between metabolites and phylogenetic clades within actinomycetes.

SUBMITTER: Croce V

PROVIDER: S-EPMC8019742 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Streptomycetes are common soil inhabitants, yet few described species are plant pathogens. While the pathogenicity mechanisms remain unclear, previous work identified a gene, nec1, which encodes a putative pathogenicity or virulence factor. nec1 and a neighboring transposase pseudogene, ORFtnp, are conserved among unrelated plant pathogens and absent from nonpathogens. The atypical GC content of nec1 suggests that it was acquired through horizontal transfer events. Our investigation of the genetic organization of regions adjacent to the 3' end of nec1 in Streptomyces scabies 84.34 identified a new insertion sequence (IS) element, IS1629, with homology to other IS elements from prokaryotic animal pathogens. IS1629 is 1,462 bp with 26-bp terminal inverted repeats and encodes a putative 431-amino-acid (aa) transposase. Transposition of IS1629 generates a 10-bp target site duplication. A 77-nucleotide (nt) sequence encompassing the start codon and upstream region of the transposase was identified which could function in the posttranscritpional regulation of transposase synthesis. A functional copy of IS1629 from S. turgidiscabies 94.09 (Hi-C-13) was selected in the transposon trap pCZA126, through its insertion into the lambda cI857 repressor. IS1629 is present in multiple copies in some S. scabies strains and is present in all S. acidiscabies and S. turgidiscabies strains examined. A second copy of IS1629 was identified between ORFtnp and nec1 in S. acidiscabies strains. The diversity of IS1629 hybridization profiles was greatest within S. scabies. IS1629 was absent from the 27 nonpathogenic Streptomyces strains tested. The genetic organization and nucleotide sequence of the nec1-IS1629 region was conserved and identical among representatives of S. acidiscabies and S. turgidiscabies. These findings support our current model for the unidirectional transfer of the ORFtnp-nec1-IS1629 locus from IS1629-containing S. scabies (type II) to S. acidiscabies and S. turgidiscabies.

Project description:With the development of synthetic biology in the field of (actinobacterial) specialized metabolism, new tools are needed for the design or refactoring of biosynthetic gene clusters. If libraries of synthetic parts (such as promoters or ribosome binding sites) and DNA cloning methods have been developed, to our knowledge, not many vectors designed for the flexible cloning of biosynthetic gene clusters have been constructed. We report here the construction of a set of 12 standardized and modular vectors designed to afford the construction or the refactoring of biosynthetic gene clusters in Streptomyces species, using a large panel of cloning methods. Three different resistance cassettes and four orthogonal integration systems are proposed. In addition, FLP recombination target sites were incorporated to allow the recycling of antibiotic markers and to limit the risks of unwanted homologous recombination in Streptomyces strains when several vectors are used. The functionality and proper integration of the vectors in three commonly used Streptomyces strains, as well as the functionality of the Flp-catalyzed excision, were all confirmed. To illustrate some possible uses of our vectors, we refactored the albonoursin gene cluster from Streptomyces noursei using the BioBrick assembly method. We also used the seamless ligase chain reaction cloning method to assemble a transcription unit in one of the vectors and genetically complement a mutant strain.IMPORTANCE One of the strategies employed today to obtain new bioactive molecules with potential applications for human health (for example, antimicrobial or anticancer agents) is synthetic biology. Synthetic biology is used to biosynthesize new unnatural specialized metabolites or to force the expression of otherwise silent natural biosynthetic gene clusters. To assist the development of synthetic biology in the field of specialized metabolism, we constructed and are offering to the community a set of vectors that were intended to facilitate DNA assembly and integration in actinobacterial chromosomes. These vectors are compatible with various DNA cloning and assembling methods. They are standardized and modular, allowing the easy exchange of a module by another one of the same nature. Although designed for the assembly or the refactoring of specialized metabolite gene clusters, they have a broader potential utility, for example, for protein production or genetic complementation.

Project description:Monitoring of pathogenic strains of Fusarium oxysporum (Fox), which cause wilt and rots on agricultural and ornamental plants, is important for predicting disease outbreaks. Since both pathogenic and non-pathogenic strains of Fox are ubiquitous and are able to colonize plant roots, detection of Fox DNA in plant material is not the ultimate proof of an ongoing infection which would cause damage to the plant. We followed the colonization of tomato plants by strains Fox f. sp. radicis-lycopersici ZUM2407 (a tomato foot and root rot pathogen), Fox f. sp. radiciscucumerinum V03-2g (a cucumber root rot pathogen) and Fox Fo47 (a well-known non-pathogenic biocontrol strain). We determined fungal DNA concentrations in tomato plantlets by quantitative PCR (qPCR) with primers complementary to the intergenic spacer region (IGS) of these three Fox strains. Two weeks after inoculation of tomato seedlings with these Fox strains, the DNA concentration of Forl ZUM2407 was five times higher than that of the non-compatible pathogen Forc V03-2g and 10 times higher than that of Fo47. In 3-week-old plantlets the concentration of Forl ZUM2407 DNA was at least 10 times higher than those of the other strains. The fungal DNA concentration, as determined by qPCR, appeared to be in good agreement with data of the score of visible symptoms of tomato foot and root rot obtained 3 weeks after inoculation of tomato with Forl ZUM2407. Our results show that targeting of the multicopy ribosomal operon results in a highly sensitive qPCR reaction for the detection of Fox DNA. Since formae speciales of Fox cannot be distinguished by comparison of ribosomal operons, detection of Fox DNA is not evidence of plant infection by a compatible pathogen. Nevertheless, the observed difference in levels of plant colonization between pathogenic and non-pathogenic strains strongly suggests that a concentration of Fox DNA in plant material above the threshold level of 0.005% is due to proliferation of pathogenic Fox.

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An Integrative Approach for the Characterization of Plant-Pathogenic Streptomyces spp. Strains Based on Metabolomic, Bioactivity, and Phylogenetic Analysis.

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