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Fusaric acid (FA), a picolinic acid derivative, is a natural substance produced by a wide variety of fungal plant pathogens belonging to the Fusarium genus. As a metabolite, fusaric acid exerts several biological activities including metal chelation, electrolyte leakage, repression of ATP synthesis, and direct toxicity on plants, animals and bacteria. Prior studies on the structure of fusaric acid revealed a co-crystal dimeric adduct between FA and 9,10-dehydrofusaric acid. During an ongoing search for signaling genes differentially regulating FA production in the fungal pathogen Fusarium oxysporum (Fo), we found that mutants lacking pheromone expression have an increased production of FA compared to the wild type strain. Noteworthy, crystallographic analysis of FA extracted from Fo culture supernatants showed that crystals are formed by a dimeric form of two FA molecules (1:1 molar stoichiometry). Overall, our results suggest that pheromone signaling in Fo is required to regulate the synthesis of fusaric acid.

Endophytic fungi (EF) can enhance both plant growth and defense barriers against pests and pathogens, contributing to the reduction of chemical pesticides and fertilizers use in agriculture. Beauveria bassiana is an entomopathogenic fungus showing endophytism in several crops, often associated with a good capacity to limit the development of pests and disease agents. However, the diversity of the protective efficacy and plant response to different strains can be remarkable and needs to be carefully assessed for the successful and predictable use of these beneficial microorganisms. This study aims to select B. bassiana strains able to colonize tomato plants as endophytes as well as to control two important disease agents, Botrytis cinerea and Alternaria alternata, and the pest aphid, Macrosiphum euphorbiae. Nine wild-type isolates and one commercial strain were screened for endophytism, then further characterized for plant-growth promotion plus inhibition of disease development and pest infestation. Four isolates proved to have a good control activity against the biotic stressors tested, but only Bb716 was also able to promote plant growth. This work provides a simple workflow for the selection of beneficial EF, paving the way towards more effective use of B. bassiana in Integrate Pest Management (IPM) of tomato.

Additional file 1: Figure S1. FTIR spectra of dextran, PLGA-COOH and PLGA-Dex10 copolymer. Carbonyl stretching band from PLGA-COOH is maintained in PLGA-Dex10. Band derived from O-H stretching is also maintained from dextran to PLGA-Dex10. Bands in the region between 1600 cm-1 to 1000 cm-1 in the spectrum of PLGA-COOH had their intensities decreased in the spectrum of PLGA-Dex10 possibly due to a concentration effect, as dextran is also abundant in the copolymer. Figure S2. FTIR of micelles. Bands derived from curcumin such as C-O bending and C-O stretching (phenol) are conserved in the spectrum of PLGA-Dex10-curc, thus confirming the incorporation of the compound in the micelle’s structure. Table S1. Infrared absorption bands assignment of micelles. Figure S3. CLSM images of GFP-expressing P. putida (A), PLGA-Dex10-curc micelles (B), the merged image generated with both P. putida and micelles (C) and inset of an area displaying bleedthrough between channels, seen as yellow spots which cannot be assigned correctly to either bacteria or micelles (D).

Stephanie Fulaz,1,* Henry Devlin,1,* Stefania Vitale,1 Laura Quinn,1 James P O’Gara,2 Eoin Casey1 1UCD School of Chemical and Bioprocess Engineering, University College Dublin, Dublin, Ireland; 2Department of Microbiology, School of Natural Sciences, National University of Ireland, Galway, Ireland*These authors contributed equally to this workCorrespondence: Eoin CaseyUCD School of Chemical and Bioprocess Engineering, University College Dublin, Belfield, Dublin 4, Dublin, IrelandEmail eoin.casey@ucd.ieBackground: Considering the timeline required for the development of novel antimicrobial drugs, increased attention should be given to repurposing old drugs and improving antimicrobial efficacy, particularly for chronic infections associated with biofilms. Methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA) are common causes of biofilm-associated infections but produce different biofilm matrices. MSSA biofilm cells are typically embedded in an extracellular polysaccharide matrix, whereas MRSA biofilms comprise predominantly of surface proteins and extracellular DNA (eDNA). Nanoparticles (NPs) have the potential to enhance the delivery of antimicrobial agents into biofilms. However, the mechanisms which influence the interactions between NPs and the biofilm matrix are not yet fully understood.Methods: To investigate the influence of NPs surface chemistry on vancomycin (VAN) encapsulation and NP entrapment in MRSA and MSSA biofilms, mesoporous silica nanoparticles (MSNs) with different surface functionalization (bare-B, amine-D, carboxyl-C, aromatic-A) were synthesised using an adapted Stöber method. The antibacterial efficacy of VAN-loaded MSNs was assessed against MRSA and MSSA biofilms.Results: The two negatively charged MSNs (MSN-B and MSN-C) showed a higher VAN loading in comparison to the positively charged MSNs (MSN-D and MSN-A). Cellular binding with MSN suspensions (0.25 mg mL− 1) correlated with the reduced viability of both MSSA and MRSA biofilm cells. This allowed the administration of low MSNs concentrations while maintaining a high local concentration of the antibiotic surrounding the bacterial cells.Conclusion: Our data suggest that by tailoring the surface functionalization of MSNs, enhanced bacterial cell targeting can be achieved, leading to a novel treatment strategy for biofilm infections.Keywords: Staphylococcus aureus, mesoporous silica nanoparticles, EPS matrix, antimicrobial, vancomycin, nanoparticle-biofilm interactions