https://pubs.rsc.org/en/content/articlepdf/2019/NP/C8NP00092A

Marine natural products.

The rhizosphere encompasses the millimeters of soil surrounding a plant root where complex biological and ecological processes occur. This review describes recent advances in elucidating the role of root exudates in interactions between plant roots and other plants, microbes, and nematodes present in the rhizosphere. Evidence indicating that root exudates may take part in the signaling events that initiate the execution of these interactions is also presented. Various positive and negative plant-plant and plant-microbe interactions are highlighted and described from the molecular to the ecosystem scale. Furthermore, methodologies to address these interactions under laboratory conditions are presented.

The Role of Root Exudates in Rhizosphere Interactions with Plants and Other Organisms

Antimicrobial activity of flavonoids

/pdf/aryl-aryl-bond-formation-one-century-after-the-discovery-of-1jdyxlkwix.pdf

Aryl-aryl bond formation one century after the discovery of the Ullmann reaction.

https://hal.archives-ouvertes.fr/hal-00567285/document

Antibiotic resistance of bacterial biofilms

Halogenated furanones produced by the benthic marine macroalga Delisea pulchra inhibit swarming motility of Serratia liquefaciens MG1. This study demonstrates that exogenously added furanones control transcription of the quorum sensing regulated gene swrA in competition with the cognate signal molecule N-butanoyl-L-homoserine lactone. This in turn results in reduced production of the surface-active compound serrawettin W2, which is crucial for surface translocation of the differentiated swarm cells. It is demonstrated that furanones interfere with interspecies communication during swarming of mixed cultures and that the mode of interference in quorum-sensing control and interspecies communication is not through inhibition of autoinducer synthesis.

How Delisea pulchra furanones affect quorum sensing and swarming motility in Serratia liquefaciens MG1

Pseudomonas fluorescens DR54 showed antagonistic properties against plant pathogenic Pythium ultimum and Rhizoctonia solani both in vitro and in planta. Antifungal activity was extractable from spent growth media, and fractionation by semi-preparative HPLC resulted in isolation of an active compound, which was identified as a new bacterial cyclic lipodepsipeptide, viscosinamide, using 1D and 2D 1H-, 13C-NMR and mass spectrometry. The new antibiotic has biosurfactant properties but differs from the known biosurfactant, viscosin, by containing glutamine rather than glutamate at the amino acid position 2 (AA2). No viscosin production was observed, however, when Ps. fluorescens DR54 was cultured in media enriched with glutamate. In vitro tests showed that purified viscosinamide also reduced fungal growth and aerial mycelium development of both P. ultimum and R. solani. Viscosinamide production by Ps. fluorescens DR54 was tightly coupled to cell proliferation in the batch cultures, as the viscosinamide produced per cell mass unit approached a constant value. In batch cultures with variable initial C, N or P nutrient levels, there were no indications of elevated viscosinamide production during starvation or maintenance of the cultures in stationary phase. Analysis of cellular fractions and spent growth media showed that a major fraction of the viscosinamide produced remained bound to the cell membrane of Ps. fluorescens DR54. The isolation, determination of structure and production characteristics of the new compound with both biosurfactant and antibiotic properties have promising perspectives for the application of Ps. fluorescens DR54 in biological control.

Viscosinamide, a new cyclic depsipeptide with surfactant and antifungal properties produced by Pseudomonas fluorescens DR54.

A nonswarming Serratia liquefaciens mutant deficient in serrawettin W2 production was constructed by transposon mutagenesis. Sequence homology indicated that insertion had occurred in gene swrA, which encodes a putative peptide synthetase. Expression of swrA is controlled by quorum sensing.

N -Acyl-l-Homoserine Lactone Autoinducers Control Production of an Extracellular Lipopeptide Biosurfactant Required for Swarming Motility of Serratia liquefaciens MG1

Aim: To study the antagonistic activity by Pseudomonas fluorescens strain 96.578 on the plant pathogenic fungus Rhizoctonia solani.



Methods and Results: Strain 96.578 produced a new cyclic lipopeptide, tensin. High tensin production per cell was detected in liquid media with glucose, mannitol or glutamate as growth substrate while fructose, sucrose and asparagine supported low production. Tensin production was nearly constant in media with different initial C levels, while low initial N contents reduced production. When applied to sugar beet seeds, strain 96.578 produced tensin during seed germination. When challenged with strain 96.578 or purified tensin, Rhizoctonia solani reduced radial mycelium extension but increased branching and rosette formation.



Conclusion: The antagonistic activity of strain 96.578 towards Rhizoctonia solani was caused by tensin.



Significance and Impact of the Study: When coated onto sugar beet seeds, tensin production by strain 96.578 could be of significant importance for inhibition of mycelial growth and seed infection by Rhizoctonia solani.

Uffe Anthoni

Papers

How Delisea pulchra furanones affect quorum sensing and swarming motility in Serratia liquefaciens MG1

Viscosinamide, a new cyclic depsipeptide with surfactant and antifungal properties produced by Pseudomonas fluorescens DR54.

N -Acyl-l-Homoserine Lactone Autoinducers Control Production of an Extracellular Lipopeptide Biosurfactant Required for Swarming Motility of Serratia liquefaciens MG1

Structure, production characteristics and fungal antagonism of tensin – a new antifungal cyclic lipopeptide from Pseudomonas fluorescens strain 96.578

Chapter Two - Naturally Occurring Cyclotryptophans and Cyclotryptamines