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ACS Chemical Biology Feb 2019Bacterial aminophenylpyrrole-derived alkaloids (APPAs) represent high value lead compounds. Pyrrolnitrin, which was developed into globally important fungicides, is the...
Bacterial aminophenylpyrrole-derived alkaloids (APPAs) represent high value lead compounds. Pyrrolnitrin, which was developed into globally important fungicides, is the only reported APPA produced by Proteobacteria. Recently, various APPAs showing diverse bioactivities were discovered from Bacteroidetes. Here, a bioinformatics and phylogenetic approach enabled the elucidation of the biosynthesis of the highly diverse APPAs in Cytophagales bacteria and their chemical diversification strategy. The biosynthetic gene clusters were identified in producer strains, and the biosynthesis was experimentally validated by heterologous expression experiments in E. coli. First, one enzyme-dependent biosynthetic step yields the tryptophan-derived precursor 3-(2'-aminophenyl)-pyrrole. Second, a spontaneous Pictet-Spengler-like coupling reaction enables the bacterial producer strains to create a library of tricyclic alkaloids, since several aldehydes can be applied as substrates. The diversity of this natural products class is further enlarged by the catalytic action of a methyltransferase, which adds one or more methyl groups to the aminophenyl intermediate.
Topics: Alkaloids; Bacteria; Molecular Structure; Pyrroles
PubMed: 30649848
DOI: 10.1021/acschembio.8b00993 -
Microbiological Research Feb 2019Pseudomonas sp. MP12 was isolated from a soil sample collected in a typical warm-temperate deciduous forest near Brescia, Northern Italy. Phylogenetic analysis...
Pseudomonas sp. MP12 was isolated from a soil sample collected in a typical warm-temperate deciduous forest near Brescia, Northern Italy. Phylogenetic analysis identified the species as Pseudomonas protegens. We evidenced in this strain the presence of the genes phlD, pltB and prnC responsible for the synthesis of the antifungal compounds 2,4-diacetylphloroglucinol (2,4-DAPG), pyoluteorin and pyrrolnitrin, respectively. P. protegens MP12 was also shown to produce siderophores and ammonia, yielded positive results with the indole-3-acetic acid test, and was capable of phosphate solubilization. Moreover, P. protegens MP12 exhibited inhibitory effects on in vitro mycelial growth of prominent grapevine (Vitis vinifera) phytopathogens such as Botrytis cinerea, Alternaria alternata, Aspergillus niger, Penicillium expansum and Neofusicoccum parvum. The strain showed activity even against Phaeomoniella chlamydospora and Phaeoacremonium aleophilum, which cause the devastating tracheomycosis/esca disease of grapevine trunks for which no efficacious control methods have been demonstrated so far. Furthermore, the MP12 strain manifested in vivo antifungal activity against B. cinerea on grapevine leaves. Culture-dependent and culture-independent analysis revealed the ability of P. protegens MP12 to efficiently and permanently colonize inner grapevine tissues. These results suggest that P. protegens MP12 could be worth of exploitation as an antifungal biocontrol agent for applications in viticulture.
Topics: Antifungal Agents; Biological Control Agents; Endophytes; Fungi; Phenols; Phloroglucinol; Plant Diseases; Plant Leaves; Pseudomonas; Pyrroles; Pyrrolnitrin; Soil Microbiology; Vitis
PubMed: 30642463
DOI: 10.1016/j.micres.2018.11.003 -
Food and Chemical Toxicology : An... Jan 2019Fludioxonil is a phenylpyrrole pesticide that is applied to fruit and vegetable crops post-harvest to minimize losses to mold, both during transport and at point of... (Review)
Review
Fludioxonil is a phenylpyrrole pesticide that is applied to fruit and vegetable crops post-harvest to minimize losses to mold, both during transport and at point of sale. Its effectiveness is reflected in the dramatic increase in its production/usage since its introduction in 1994, an increase that has peaked in recent years as it became licenced for use abroad. Recently, doubts as to the nature of its mechanism of action have been raised. Given that the pesticide has long been known to induce stress intermediates in target and non-target organisms alike, the lack of a firmly established mechanism might be cause for concern. Troubling reports further delineate a capacity to disrupt hepatic, endocrine and neurological systems, indicating that fludioxonil may represent a health threat to consumers. In the absence of a clear, safe mechanism of action, fludioxonil should be re-evaluated for its potential to impact human health.
Topics: Consumer Product Safety; Crops, Agricultural; Dioxoles; Food Contamination; Fungicides, Industrial; Humans; Pyrroles
PubMed: 30458269
DOI: 10.1016/j.fct.2018.11.037 -
Canadian Journal of Microbiology Mar 2019A biocontrol bacterium, Pseudomonas chlororaphis O6 promotes plant health through multifaceted mechanisms. In this study, we used P. chlororaphis O6 mutants to examine...
A biocontrol bacterium, Pseudomonas chlororaphis O6 promotes plant health through multifaceted mechanisms. In this study, we used P. chlororaphis O6 mutants to examine metabolites with aphicidal activity. Direct application of intact P. chlororaphis cells to the surface of second-instar nymphs of the green peach aphid resulted in no mortality. However, nymphs died when exposed only to the volatiles produced by the P. chlororaphis O6 wild-type strain grown on rich media. Mutants lacking the production of two antibiotics, phenazine and pyrrolnitrin, or the insect toxin FitD retained the aphicidal potential of the wild-type strain. However, the volatiles produced by mutants deficient in the production of hydrogen cyanide (HCN) or defective in the synthesis of the global regulator GacS, which regulates HCN synthesis, showed no aphicidal activity. Direct application of potassium cyanide caused mortality of green peach aphid nymphs. These results indicate that HCN production by a plant probiotic is involved in preventing insect growth.
Topics: Animals; Aphids; Hydrogen Cyanide; Insecticides; Pseudomonas chlororaphis
PubMed: 30398901
DOI: 10.1139/cjm-2018-0372 -
Frontiers in Microbiology 2018Natural control of phytopathogenic microorganisms is assumed as a priority function of the commensal plant microbiota. In this study, the suitability of fluorescent...
Natural control of phytopathogenic microorganisms is assumed as a priority function of the commensal plant microbiota. In this study, the suitability of fluorescent pseudomonads in the phyllosphere of crop plants as natural control agents was evaluated. Under field conditions, ears of winter wheat were found to be colonized with high consistency and at a high density by pseudomonads at the late milk dough stage. Isolates of these bacteria were evaluated for their potential to protect the plants from phytopathogenic and fungi. More isolates were antagonistically active against alternaria than against fusaria in the dual culture test. The alternaria responded species-specifically and more sensitively to bacterial antagonism than the strain-specific reacting fusaria. A total of 110 randomly selected isolates were screened for genes involved in the biosynthesis of the antibiotics 2,4-diacetylphloroglucinol, phenazine-1-carboxylic acid, pyoluteorin, and pyrrolnitrin. The key gene for production of the phloroglucinol was found in none of these isolates. At least one of the genes, encoding the biosynthesis of the other antibiotics was detected in 81% of the isolates tested. However, the antagonistic effect found in the dual culture assay was not necessarily associated with the presence of these antibiotic genes. Wheat grains as natural substrate were inoculated with selected antagonistic isolates and and strains, respectively. The fungal growth was only slightly delayed, but the mycotoxin production was significantly reduced in most of these approaches. In conclusion, the distribution of phytopathogenic fungi of the genera and in the field is unlikely to be inhibited by naturally occurring pseudomonads, also because the bacterial antagonists were not evenly distributed in the field. However, pseudomonads can reduce the production of and mycotoxins in wheat grains and thus have the potential to improve the crop quality.
PubMed: 30250459
DOI: 10.3389/fmicb.2018.02124 -
Microbiological Research Oct 2018Fusarium graminearum is the major causal agent of Fusarium head blight (FHB) disease in cereal crops worldwide. Infection with this fungal phytopathogen can regularly...
Fusarium graminearum is the major causal agent of Fusarium head blight (FHB) disease in cereal crops worldwide. Infection with this fungal phytopathogen can regularly cause severe yield and quality losses and mycotoxin contamination in grains. In previous other studies, one research group reported that pyrrolnitrin had an ability to suppress of mycelial growth of F. graminearum. Other groups revealed that phenazine-1-carboxamide, a derivative of phenazine-1-carboxylic acid, could also inhibit the growth of F. graminearum and showed great potentials in the bioprotection of crops from FHB disease. In our recent work with Pseudomonas chlororaphis strain G05, however, we found that although the phz operon (phenazine biosynthetic gene cluster) was knocked out, the phenazine-deficient mutant G05Δphz still exhibited effective inhibition of the mycelial growth of some fungal phytopathogens in pathogen inhibition assay, especially including F. graminearum, Colletotrichum gloeosporioides, Botrytis cinerea. With our further investigations, including deletion and complementation of the prn operon (pyrrolnitrin biosynthetic gene cluster), purification and identification of fungal compounds, we first verified that not phenazines but pyrrolnitrin biosynthesized in P. chlororaphis G05 plays an essential role in growth suppression of F. graminearum and the bioprotection of cereal crops against FHB disease.
Topics: Bacterial Proteins; Botrytis; Colletotrichum; Crops, Agricultural; Edible Grain; Fungicides, Industrial; Fusarium; Gene Expression Regulation, Bacterial; Gene Knockout Techniques; Genes, Fungal; Multigene Family; Mutation; Mycelium; Operon; Pest Control, Biological; Phenazines; Plant Diseases; Pseudomonas chlororaphis; Pyrrolnitrin
PubMed: 30172309
DOI: 10.1016/j.micres.2018.06.008 -
Applied Microbiology and Biotechnology Nov 2018The rhizobacterium Pseudomonas protegens H78 biosynthesizes a number of antibiotic compounds, including pyoluteorin, 2,4-diacetylphloroglucinol, and pyrrolnitrin. Here,...
The rhizobacterium Pseudomonas protegens H78 biosynthesizes a number of antibiotic compounds, including pyoluteorin, 2,4-diacetylphloroglucinol, and pyrrolnitrin. Here, we investigated the global regulatory function of the nitrogen metabolism-related sigma factor RpoN in P. protegens H78 through RNA-seq and phenotypic analysis. During the mid- to late-log growth phase, transcriptomic profiling revealed that 562 genes were significantly upregulated, and 502 genes were downregulated by at least twofold at the RNA level in the rpoN deletion mutant in comparison with the wild-type strain H78. With respect to antibiotics, Plt biosynthesis and the expression of its operon were positively regulated, while Prn biosynthesis and the expression of its operon were negatively regulated by RpoN. RpoN is responsible for the global activation of operons involved in flagellar biogenesis and assembly, biofilm formation, and bacterial mobility. In contrast, RpoN was shown to negatively control a number of secretion system operons including one type VI secretion system operon (H1-T6SS), two pilus biogenesis operons (Flp/Tad-T4b pili and Csu-T1 pili), and one polysaccharide biosynthetic operon (psl). In addition, two operons that are involved in mannitol and inositol utilization are under the positive regulation of RpoN. Consistent with this result, the ability of H78 to utilize mannitol or inositol as a sole carbon source is positively influenced by RpoN. Taken together, the RpoN-mediated global regulation is mainly involved in flagellar biogenesis and assembly, bacterial mobility, biofilm formation, antibiotic biosynthesis, secretion systems, and carbon utilization in P. protegens H78.
Topics: Anti-Bacterial Agents; Bacterial Proteins; Biofilms; Carbon; Fimbriae, Bacterial; Gene Expression Regulation, Bacterial; Operon; Pseudomonas; RNA Polymerase Sigma 54
PubMed: 30128583
DOI: 10.1007/s00253-018-9282-0 -
Microbial Ecology May 2019This work reports the comparison of the genome sequence and the ability to inhibit fungal growth of two Pseudomonas protegens related strains that were isolated from the...
This work reports the comparison of the genome sequence and the ability to inhibit fungal growth of two Pseudomonas protegens related strains that were isolated from the same hydroponic culture of lamb's lettuce. The two strains were very similar in their core genome but one strain, Pf4, contained three gene clusters for the production of secondary metabolites, i.e., pyoluteorin (plt), pyrrolnitrin (prn), and rhizoxin (rzx), that were missing in the other strain, Pf11. The difference between the two strains was not due to simple insertion events, but to a relatively complex differentiation focused on the accessory genomes. In dual culture assays, both strains inhibited nearly all tested fungal strains, yet Pf4 exerted a significantly stronger fungal growth inhibition than Pf11. In addition to the differences in the secondary metabolite production associated genes abundance, the genome of Pf4 was more stable, smaller in size and with a lower number of transposons. The preservation of a dynamic equilibrium within natural populations of different strains comprised in the same species but differing in their secondary metabolite repertoire and in their genome stability may be functional to the adaptation to environmental changes.
Topics: Antifungal Agents; Genome, Bacterial; Hydroponics; Pseudomonas; Pythium; Rhizoctonia
PubMed: 30088023
DOI: 10.1007/s00248-018-1238-5 -
Journal of Basic Microbiology Sep 2018In previous studies with Pseudomonas chlororaphis G05, two operons (phzABCDEFG and prnABCD) were confirmed to respectively encode enzymes for biosynthesis of...
In previous studies with Pseudomonas chlororaphis G05, two operons (phzABCDEFG and prnABCD) were confirmed to respectively encode enzymes for biosynthesis of phenazine-1-carboxylic acid and pyrrolnitrin that mainly contributed to suppression of some fungal phytopathogens. Although some regulators were identified to govern their expression, it is not known how two operons coordinately interact. By constructing the phz- or/and prn- deletion mutants, we found that in comparison with the wild-type strain G05, phenazine-1-carboxylic acid production in the mutant G05Δprn obviously decreased in GA broth in the absence of prn, and pyrrolnitrin production in the mutant G05Δphz remarkably declined in the absence of phz. By generating the phzA and prnA transcriptional and translational fusions with a truncated lacZ on shuttle vector or on the chromosome, we found that expression of the phz or prn operon was correspondingly increased in the presence of the prn or phz operon at the post-transcriptional level, not at the transcriptional level. These results indicated that the presence of one operon would promote the expression of the other one operon between the phz and prn. This reciprocal enhancement would keep the strain G05 producing more different antifungal compounds coordinately and living better with growth suppression of other microorganisms.
Topics: Antifungal Agents; Bacterial Proteins; Gene Expression Regulation, Bacterial; Mutation; Operon; Phenazines; Pseudomonas chlororaphis; Pyrrolnitrin
PubMed: 29995319
DOI: 10.1002/jobm.201800206 -
Beilstein Journal of Organic Chemistry 2018Exploration of rhizobacteria of the genus as an under-tapped resource of bioactive molecules resulted in the isolation of two new antimicrobial 2-alkyl-4-quinolones....
Exploration of rhizobacteria of the genus as an under-tapped resource of bioactive molecules resulted in the isolation of two new antimicrobial 2-alkyl-4-quinolones. ()-2-(Hept-2-en-1-yl)quinolin-4(1)-one () and ()-2-(non-2-en-1-yl)quinolin-4(1)-one () were isolated from the culture broth of strain MBAF1239 together with four known alkylquinolones ( and -), pyrrolnitrin (), and BN-227 (). The structures of and were unambiguously characterized using NMR spectroscopy and mass spectrometry. Compounds - inhibited the growth of the marine bacterium , an etiological agent of skin ulcers in marine fish, offering new opportunities to develop antibacterial drugs for fish farming.
PubMed: 29977408
DOI: 10.3762/bjoc.14.122