Domenico Vitullo

Antifungal Lipopeptides from Bacillus amyloliquefaciens Strain BO7

Three new lipopeptides (1-3) were isolated from the organic extract of Bacillus amyloliquefaciens strain (BO7). These compounds represented the major constituents (>60%) of the total cell lipids extractable with CHCl(3)/MeOH (2:1). Elucidation of their chemical structure was carried out by spectroscopic analyses, including 1D and 2D NMR spectroscopy, mass spectrometry (MS), and secondary ion mass spectrometry (MS/MS), along with chemical degradation. The compounds are members of the surfactins family and are based on the heptapeptide Glu-Leu-Leu-Ala-Asp-Leu-Leu, N-acylated to the N-terminal by an (R)-3-hydroxy fatty acid with linear alkyl chains from 16:0 to 18:0 (1-3, respectively). An ester bond between the 3-hydroxyl group of the fatty acid and the carboxylic group of the C-terminal amino acid closes a 13-membered lactone ring. The bacterial lipopeptides, particularly compound 3, displayed strong and dose-dependent antifungal activity against the plant pathogenic fungus Fusarium oxysporum.

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.

A microbial consortium in the rhizosphere as a new biocontrol approach against fusarium decline of chickpea

Background and aimChickpea (Cicer arietinum L.) is an important crop worldwide. Fungi of the genus Fusarium are among the most aggressive pathogens of chickpea, causing plant wilt and/or root rot. The incidence of soilborne pathogens can be reduced by increasing the microbial diversity in the rhizosphere. To improve soil suppressiveness against Fusarium spp., we optimized a microbial consortium consisting in a mixture of bacterial isolates selected from the naturally occurring microflora in the chickpea rhizosphere.MethodsBeneficial rhizobacteria were selected based on i) their mutual compatibility when grown in mixture, ii) antagonistic activity against F. oxysporum f. sp. ciceris race 0 and F. solani f. sp. pisi and iii) growth promoting capacity on chickpea.ResultsThe best results were obtained by using a consortium consisting of a mixture of four bacterial isolates: Serratia marcescens isolate 59, Pseudomonas fluorescens isolate 57, Rahnella aquatilis isolate 36 and Bacillus amyloliquefaciens isolate 63.ConclusionsThis microbial consortium efficiently controlled both Fusarium pathogens, with a consistently higher efficacy compared to those of bacteria applied individually. The putative mechanisms involved in the interaction between antagonists, plant and Fusarium are discussed.

Milkwort (Polygala myrtifolia L.) decline is caused by Fusarium oxysporum and F. solani in Southern Italy

Milkwort (Polygala myrtifolia L.) is an ornamental shrub of commercial importance in temperate climatic zones. For this vegetal species very few diseases have been reported, except for two diseases caused by Cylindrocladium pauciramosum in Europe (mainly in Italy and Spain) and Cucumber mosaic virus (CMV) in Italy. A severe decline of milkwort plants was for the first time observed in nurseries of Southern Italy (Termoli and Campomarino, Molise). Affected plants appeared from partially to completely wilted, stunted and weakly chlorotic. In symptomatic plants Fusarium sp. colonies were consistently isolated from crown, basal stem, and root lesions. According to their morphological characters and genomic differentiation by Polymerase Chain Reaction (PCR) of ribosomal DNA, the most frequent and representative fungal isolates were identified as Fusarium oxysporum and F. solani. The etiology of this milkwort disease was proved by fulfilling Koch’s postulates on artificially inoculated milkwort healthy plants. This is the first record of milkwort wilt caused by pathogenic Fusarium species.