Inhibitory effects of extracellular self-DNA: a general biological process?

Self-inhibition of growth has been observed in different organisms, but an underlying common mechanism has not been proposed so far. Recently, extracellular DNA (exDNA) has been reported as species-specific growth inhibitor in plants and proposed as an explanation of negative plant-soil feedback. In this work the effect of exDNA was tested on different species to assess the occurrence of such inhibition in organisms other than plants. Bioassays were performed on six species of different taxonomic groups, including bacteria, fungi, algae, plants, protozoa and insects. Treatments consisted in the addition to the growth substrate of conspecific and heterologous DNA at different concentration levels. Results showed that treatments with conspecific DNA always produced a concentration dependent growth inhibition, which instead was not observed in the case of heterologous DNA. Reported evidence suggests the generality of the observed phenomenon which opens new perspectives in the context of self-inhibition processes. Moreover, the existence of a general species-specific biological effect of exDNA raises interesting questions on its possible involvement in self-recognition mechanisms. Further investigation at molecular level will be required to unravel the specific functioning of the observed inhibitory effects.

Inhibitory and toxic effects of extracellular self-DNA in litter: a mechanism for negative plant-soil feedbacks?

Plant-soil negative feedback (NF) is recognized as an important factor affecting plant communities. The objectives of this work were to assess the effects of litter phytotoxicity and autotoxicity on root proliferation, and to test the hypothesis that DNA is a driver of litter autotoxicity and plant-soil NF. The inhibitory effect of decomposed litter was studied in different bioassays. Litter biochemical changes were evaluated with nuclear magnetic resonance (NMR) spectroscopy. DNA accumulation in litter and soil was measured and DNA toxicity was assessed in laboratory experiments. Undecomposed litter caused nonspecific inhibition of root growth, while autotoxicity was produced by aged litter. The addition of activated carbon (AC) removed phytotoxicity, but was ineffective against autotoxicity. Phytotoxicity was related to known labile allelopathic compounds. Restricted (13) C NMR signals related to nucleic acids were the only ones negatively correlated with root growth on conspecific substrates. DNA accumulation was observed in both litter decomposition and soil history experiments. Extracted total DNA showed evident species-specific toxicity. Results indicate a general occurrence of litter autotoxicity related to the exposure to fragmented self-DNA. The evidence also suggests the involvement of accumulated extracellular DNA in plant-soil NF. Further studies are needed to further investigate this unexpected function of extracellular DNA at the ecosystem level and related cellular and molecular mechanisms.

Antifungal cyclic lipopeptides from Bacillus amyloliquefaciens strain BO5A.

A bioassay-guided fractionation of Bacillus amyloliquefaciens strain BO5A afforded the isolation of two new cyclic lipopeptides (1 and 2) as the major lipid constituents (>60%) of the CHCl3-MeOH (2:1) extract. The chemical structures of the isolated metabolites were elucidated by spectroscopic methods, including 1D and 2D NMR spectroscopy, mass spectrometry (MS), secondary ion mass spectrometry (MS1, MS2), and chemical degradation. The compounds are members of the surfactins family and are based on a heptapeptide chain composed by Glu-Val-Leu-Val-Asp-Leu-Leu. Its N-terminal end is N-acylated by an (R)-3-hydroxy fatty acid with linear alkyl chains of 16:0 and 15:0 (1 and 2, respectively). The 3-hydroxyl group closes a 25-membered lactone ring with the carboxylic group of the C-terminal amino acid. The isolated compounds were tested for their inhibitory activity against the four pathogenic fungi Fusarium oxysporum, Aspergillus niger, Botrytis cinerea, and Penicillium italicum and the biocontrol fungus Trichoderma harzianum. Compound 2 displayed activity against all tested pathogens.

Pathologies of imagination and affectivity: the genesis of the unconscious in Marc Richir.

In their recent work in phenomenological psychopathology, Andreas Rosén Rasmussen and Joseph Parnas argue that there is an expressive relationship between the anomalies of imagination reported in schizophrenic spectrum disorders (SSDs) and an underlying generative self- or ipseity disorder. The authors build their argument on an updated review of the phenomenological model of consciousness, by which each experience articulates itself in ipseity according to its modality. Therefore, they explain imagination as the figuration of an absent object mediated by the imaginary and accompanied by a sense of irreality. Finally, by drawing on patients' descriptions, Rasmussen and Parnas show that SSD imagination disorders testify to the breakdown of this model of consciousness. In this article, I aim to complexify the scenario summarized above by focusing on the contribution made by the phenomenologist Marc Richir in his late masterwork Phantasia, imagination et affectivité (2004). To this end, I examine the genetic analyses of the pathologies of the imaginary that Richir develops through a non-standard interpretation of Husserl's phenomenology of imagination (in particular, Hua XXIII, text n.16, 1912). In my examination, I aim to unfold an alternative model of consciousness that (a) is based on the gap between the architectonic registers of phantasia and imagination (and the corresponding stages of sense-making and the institution of sense), (b) takes account of the role of affectivity in those registers, (c) places the pathologies of the imaginary in the quasi-empathy that characterizes the missed encounter with the other, and (d) links the institution of these pathologies with the psychoanalytic account of the fixation of the phantasm.

NMR Metabolomics and Chemometrics of Lettuce, Lactuca sativa L., under Different Foliar Organic Fertilization Treatments.

Lettuce plants were grown in a greenhouse affected by the fungal pathogen Fusarium oxysporum to test the effects on plant metabolomics by different organic treatments. Three foliar application treatments were applied: a commercial compost tea made of aerobically fermented plant organic matter, a pure lyophilized microalga Artrospira platensis, commonly named spirulina, and the same microalga previously exposed during its culture to a natural uptake from medium enriched with F. oxysporum fragmented DNA (NAT). The experiment is the first attempt to observe in field conditions, the use and effects of a natural microbial library as a carrier of pathogenic fungal DNA for disease control. Untargeted NMR metabolomics and chemometrics showed that foliar organic application significantly reduced fumaric and formic acids, aromatic amino acids, and nucleosides, while increasing ethanolamine. A strong decrease in phenolic acids and an increase in citric acid and glutamine were specifically observed in the NAT treatment. It is noteworthy that the exposure of a known biostimulant microalga to fungal DNA in its culture medium was sufficient to induce detectable changes in the metabolomic profiles of the fertilized plants. These findings deserve further investigation to assess the potential relevance of the presented approach in the field of crop biostimulation and biocontrol of plant pathogens.

Plant-Based Biostimulants Influence the Agronomical, Physiological, and Qualitative Responses of Baby Rocket Leaves under Diverse Nitrogen Conditions.

Nitrogen is the primary technical means responsible for food production increase, but on the other hand, wise management is needed because its excessive use can have a negative impact on the environment and on green leafy vegetable quality, such as that rocket. Rocket has the characteristics of accumulating nitrate in leaves with possible impacts on human health. In order to overcome this issue, researchers are focusing their attention on the use of alternative means, such as plant biostimulant application. The scope of this study was to assess the effect of legume-derived protein hydrolysate(LDPH) and tropical plant extract(TPE), combined with various doses of nitrogen (0 kg ha-1 non-fertilized; N0); 60 kg ha-1 (sub-optimal; N1); 80 kg ha-1 (optimal; N2); and 100 kg ha-1 (supra-optimal; N3)), in order to reduce nitrogen use, boost yield, and enhance the chemical and nutritional value of leaves without significantly accumulating nitrate. Both vegetal-based plant biostimulants enhanced plant growth, boosted the marketable yield (especially at N0 and N1 levels, by 38.2% and 28.2%, respectively, compared to the non-treated control), and increased the SPAD (Soil Plant Analysis Development) index and leaf pigments content, such as chlorophyll and carotenoids, especially in treated-LDPH rocket. The plant-based biostimulants also produced a major amplification in lipophilic antioxidant activity (+ 48%) and total ascorbic acid content (average + 95.6%), especially at low nitrogen fertilization levels, and maintained nitrate content under the legal European Comission limits.

A microsatellite based method for quantification of fungi in decomposing plant material elucidates the role of Fusarium graminearum DON production in the saprophytic competition with Trichoderma atroviride in maize tissue microcosms.

Common PCR assays for quantification of fungi in living plants cannot be used to study saprophytic colonization of fungi because plant decomposition releases PCR-inhibiting substances and saprophytes degrade the plant DNA which could serve as internal standard. The microsatellite PCR assays presented here overcome these problems by spiking samples prior to DNA extraction with mycelium of a reference strain. PCR with fluorescent primers co-amplifies microsatellite fragments of different length from target and reference strains. These fragments were separated in a capillary sequencer with fluorescence detection. The target/reference ratio of fluorescence signal was used to calculate target biomass in the sample. Such PCR assays were developed for the mycotoxin deoxynivalenol (DON)-producing wheat and maize pathogen Fusarium graminearum and the biocontrol agent Trichoderma atroviride, using new microsatellite markers. In contrast to real-time PCR assays, the novel PCR assays showed reliable fungal biomass quantification in samples with differentially decomposed plant tissue. The PCR assays were used to quantify the two fungi after competitive colonization of autoclaved maize leaf tissue in microcosms. Using a DON-producing F. graminearum wild-type strain and its nontoxigenic mutant we found no evidence for a role of DON production in F. graminearum defense against T. atroviride. The presence of T. atroviride resulted in a 36% lower wild-type DON production per biomass.

Spirostane, furostane and cholestane saponins from Persian leek with antifungal activity.

A phytochemical investigation of the seeds of Persian leek afforded the isolation of two new spirostane glycosides, persicosides A (1) and B (2), four new furostane glycosides, isolated as a couple of inseparable mixture, persicosides C1/C2 (3a/3b) and D1/D2 (4a/4b), one cholestane glycoside, persicoside E (5), together with the furostane glycosides ceposides A1/A2 and C1/C2 (6a/6b and 7a/7b), tropeosides A1/A2 and B1/B2 (8a/8b and 9a/9b), and ascalonicoside A1/A2 (10a/10b), already described in white onion, red Tropea onion, and shallot, respectively. Structure elucidation of the compounds was carried out by comprehensive spectroscopic analyses, including 2D NMR spectroscopy and MS spectrometry, and by chemical evidences. The chemical structure of new compounds were identified as (25S)-spirostan-2α,3ß,6ß-triol 3-O-[ß-d-glucopyranosyl-(1→3)] [ß-d-xylopyranosyl-(1→2)]-ß-d-glucopyranosyl-(1→4)-ß-d-galactopyranoside (1), (25S)-spirostan-2α,3ß,6ß-triol 3-O-[ß-d-xylopyranosyl-(1→3)] [α-l-rhamnopyranosyl-(1→2)]-ß-d-glucopyranosyl-(1→4)-O-ß-d-galactopyranoside (2), furosta-1ß,3ß,22ξ,26-tetraol 5-en 1-O-ß-d-glucopyranosyl (1→3)-ß-d-glucopyranosyl (1→2)-ß-d-galactopyranosyl 26-O-α-l-rhamnopyranosyl (1→2)-ß-d-galactopyranoside (3a,3b), furosta-2α,3ß,22ξ,26-tetraol 3-O-ß-d-glucopyranosyl (1→3)-ß-d-glucopyranosyl (1→2)-ß-d-galactopyranosyl 26-O-ß-d-glucopyranoside (4a,4b), (22S)-cholesta-1ß,3ß,16ß,22ß-tetraol 5-en 1-O-α-l-rhamnopyranosyl 16-O-α-l-rhamnopyranosyl (1→2)-ß-d-galactopyranoside (5). Antifungal activity of the isolated compounds was evaluated against the fungal pathogens, Penicillium italicum, Aspergillus niger, Trichoderma harzianum and Botrytis cinerea. Persicosides A and B showed the higher activity on the tested fungi highlighting the positive effect of the spirostane skeleton on the antifungal activity.