Bivalent Metal-Chelating Properties of Harzianic Acid Produced by Trichoderma pleuroticola Associated to the Gastropod Melarhaphe neritoides.

Harzianic acid is a secondary metabolite of Trichoderma, structurally belonging to the dienyltetramic acid subgroup of the tetramic acids. Biological activities of harzianic acid are of great interest for its antimicrobial and plant growth-promoting activities, which might be related to its chelating properties. In the present work harzianic acid, isolated from cultures of a strain of Trichoderma pleuroticola associated to the gastropod Melarhaphe neritoides, was studied as a complexant agent of a number of biologically relevant transition metals (i.e., Zn2+, Fe2+, Cu2+, and Mn2+), using UV-VIS, potentiometry, MS and NMR techniques. Our findings show the coordination capacity of harzianic acid toward the above cations through the formation of neutral or charged complexes in a variable ratio depending on the metal and pH conditions.

Antimicrobial activity of harzianic acid against Staphylococcus pseudintermedius.

The emerging concern about the increase of antibiotic resistance has encouraged research efforts to develop effective alternatives to counteract bacterial infections. Herein, we studied a new perspective to therapeutic treatment against Staphylococcus pseudintermedius, an opportunistic pathogen documented as the major cause of skin, ear, and post-operative bacterial infections in dogs and cats. Antimicrobial activity of secondary metabolites produced by selected microbial strains belonging to Trichoderma, Talaromyces, Clonostachys and Coniothyrium fungal genera has been tested against S. pseudintermedius. Several extracts, particularly those obtained from Trichoderma harzianum E45 and ET45, showed a significant antimicrobial activity towards S. pseudintermedius methicillin-resistant (MRSP) and methicillin-susceptible (MSSP) strains. Bioassay-guided fractionation of E45 and ET45 extracts allowed to isolate harzianic acid as the major compound responsible for biological activities (e.g. antimicrobial, antibiofilm formation and biofilm disaggregation).

Methyl t-butyl ether-degrading bacteria for bioremediation and biocontrol purposes.

A total of fifteen potential methyl t-butyl ether (MtBE)-degrading bacterial strains were isolated from contaminated soil. They have been identified as belonging to the genera Bacillus, Pseudomonas, Kocuria, Janibacter, Starkeya, Bosea, Mycolicibacterium, and Rhodovarius. Bacillus aryabhattai R1B, S. novella R8b, and M. mucogenicum R8i were able to grow using MtBE as carbon source, exhibiting different growth behavior and contaminant degradation ability. Their biocontrol ability was tested against various fungal pathogens. Both S. novella R8b and B. aryabhattai were effective in reducing the development of necrotic areas on leaves within 48 hours from Botritys cinerea and Alternaria alternata inoculation. Whereas, M. mucogenicum effectively controlled B. cinerea after 72 hours. Similar results were achieved using Pythium ultimum, in which the application of isolated bacteria increased seed germination. Only M. mucogenicum elicited tomato plants resistance against B. cinerea. This is the first report describing the occurrence of bioremediation and biocontrol activities in M. mucogenicum, B. aryabhattai and S. novella species. The production of maculosin and its antibiotic activity against Rhizoctonia solani has been reported for first time from S. novella. Our results highlight the importance of multidisciplinary approaches to achieve a consistent selection of bacterial strains useful for plant protection and bioremediation purposes.