Production of toxic metabolites by two strains of Lasiodiplodia theobromae, isolated from a coconut tree and a human patient

ABSTRACT

Lasiodiplodia theobromae is a phytopathogenic fungus that causes diseases not only in a broad number of plant hosts but also occasionally in humans. The capacity of L. theobromae to produce bioactive metabolites at 25 C (environmental mean temperature) and at 37 C (body mean temperature) was investigated. Two strains, CAA019 and CBS339.90, isolated respectively from a coconut tree and a human patient were characterized. The phytotoxicity and cytotoxicity (on mammalian cells) of the secretomes of both strains of L. theobromae were investigated. Also, phytotoxicity and cytotoxicity of pure compounds were evaluated. The phytotoxicity of the secretome of strain CAA019 was higher than the phytotoxicity of the secretome of strain CBS339.90 at 25 C. However, the phytotoxicity for both strains decreased when they were grown at 37 C. Only the secretome of strain CBS339.90 grown at 37 C induced up to 90% Vero and 3T3 cell mortality. This supports the presence of different metabolites in the secretome of strains CAA019 and CBS339.90. Metabolites typical of L. theobromae were isolated and identified from organic extracts of the secretome of both strains (e.g., 3-indolecarboxylic acid, jasmonic acid, lasiodiplodin, four substituted 2-dihydrofuranones, two melleins, and cyclo-(Trp-Ala)). Also, metabolites such as scytalone, not previously reported for this species, were isolated and identified. Metabolite production is affected by strain and temperature. In fact, some metabolites are strain specific (e.g., lasiodiplodin) and some metabolites are temperature specific (e.g., jasmonic acid). Although more strains should be characterized, it may be anticipated that temperature tuning of secondary-metabolite production emerges as a putative contributing factor in the modulation of L. theobromae pathogenicity towards plants, and also towards mammalian cells.

KEYWORDS:

• Cytotoxicity
• global changes
• phytopathogenic fungi
• phytotoxicity
• secondary metabolites
• temperature

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Funding

This study was supported by FEDER funding through COMPETE program and by national funding through FCT within the research project ALIEN (PTDC/AGR-PRO/2183/2014–POCI-01-0145-FEDER-016788) and the research unit CESAM (UID/AMB/50017–POCI-01-0145-FEDER-007638). The authors acknowledge FCT financial support to A. Alves (IF/00835/2013), A. C. Esteves (BPD/102572/2014) and C. Félix (BD/97613/2013). The authors also thank the support of COST Action FA1303: Sustainable control of grapevine trunk diseases. COST Action is supported by the EU RTD Framework program, and ESF provides the COST office through an EC contract.