Composição volátil e atividade antimicrobiana de fungos endofíticos da oliveira

Mestrado em cooperação com a Universidade de SalamancaNos últimos anos, os fungos endófitos associados a diversas espécies de plantas, têm sido explorados como potenciais produtores de novos compostos antimicrobianos para superar os grandes problemas de resistência dos microrganismos aos antibióticos/antifúngicos. No entanto, estudos sobre fungos endófitos de Olea europaea L., são ausentes. Neste trabalho, foi estudado o potencial antimicrobiano de três fungos endófitos de O. europaea e avaliado o efeito da planta hospedeira neste potencial. Os compostos voláteis produzidos pelos endófitos foram identificados por cromatografia gasosa / espectrometria de massa, e posteriormente correlacionados com a atividade antimicrobiana. Os fungos endófitos, Penicillium commune e Penicillium canescens foram os mais eficazes na inibição de bactérias [até 2,7 vezes mais em comparação com cloranfenicol (30 μg/mL)] enquanto que Alternaria alternata foi mais eficaz na inibição de leveduras [até 8,0 vezes mais em comparação com o fluconazol (25 μg/mL)]. Esta espécie foi também a que apresentou o maior espetro de atividade na concentração minima inibitória ≤ 0,095 mg/mL. O extracto de planta hospedeira mostrou desempenhar um papel importante na actividade antimicrobiana dos endófitos, dependendo da espécie. A análise do perfil volátil de A. alternata e P. canescens, permitiu identificar seis compostos voláteis, sendo 3-metil-1-butanol e fenil-etil álcool os mais abundantes. Outros compostos voláteis identificados incluiram o 3-metil-1-butanol acetato, 1-octen-3-ol, β-cedreno e thujopsene. Através da análise de componentes principais, foi possível verificar que a atividade antimicrobiana exibida por A. alternata pode estar relacionada com a sua composição volátil, principalmente devido ao elevado teor de voláteis antimicrobianos 3-metil-1-butanol e fenil-etil álcool. Em geral, os resultados obtidos destacaram o potencial antimicrobiano de fungos endofíticos de O. europaea e a possibilidade de serem explorados pelos seus agentes antimicrobianos.In recent years, fungal endophytes from diverse host plant species, have been examined as potential producers of novel antimicrobials to overcome the growing problems of drug resistance in microorganisms. Studies on fungal endophytes from Olea europaea L. are however absent. In this study, the antimicrobial potential of three fungal endophytes from O. europaea was studied and the host plant effect in the antimicrobial activity was examined. The volatile compounds produced by endophytes were identified by gas chromatography/mass spectrometry and further correlated with the antimicrobial activity. Both Penicillium commune and Penicillium canescens were most effective in inhibiting bacteria [in average up to 2.7-fold compared to chloramphenicol (30 μg/mL)] whereas Alternaria alternata was most effective in inhibiting yeasts [in average up to 8.0-fold compared to fluconazole (25 μg/mL)]. This specie also displayed the widest spectrum of anti-microorganisms at MIC ≤ 0.095 mg/mL. Host plant extract showed to play an important role in the antimicrobial activity of the endophytes, depending on the species. From the volatile composition of A. alternata and P. canescens, six volatiles were identified, being 3-methyl-1-butanol and phenylethyl alcohols the most abundant. Others volatiles like 3-methyl-1-butanol acetate, 1-octen-3-ol, β-cedrene and thujopsene were identified. By a principal component analysis it was possible to verify that the antimicrobial activity displayed by A. alternata may be related to its volatile composition, mainly due to the high content in the antimicrobial volatiles 3-methyl-1-butanol and phenylethyl alcohol. Overall the obtained results highlighted the antimicrobial potential of endophytic fungi from O. europaea and their possibility to be exploited for their antimicrobial agents.Este trabalho é financiado por Fundos Nacionais através da FCT – Fundação para a Ciência e a Tecnologia no âmbito do projeto “EndoBio - Isolamento e seleção de fungos endofíticos da oliveira para luta biológica contra Colletotrichum acutatum e Verticillium dahliae” (PTDC/AGR-PRO/4354/2012)

Antimicrobial activity of endophytic fungi from olive tree leaves

In this study, the antimicrobial potential of three fungal endophytes from leaves of Olea europaea L. was evaluated and the host plant extract effect in the antimicrobial activity was examined. The volatile compounds produced by endophytes were identified by GC/MS and further correlated with the antimicrobial activity. In potato dextrose agar, both Penicillium commune and Penicillium canescens were the most effective inhibiting Gram-positive and -negative bacteria (up to 2.7-fold compared to 30 µg/mL chloramphenicol), whereas Alternaria alternata was most effective inhibiting yeasts (up to 8.0-fold compared to 25 μg/mL fluconazole). The presence of aqueous leaf extract in culture medium showed to induce or repress the antimicrobial activity, depending on the endophytic species. In the next step, various organic extracts from both A. alternata mycelium and cultured broth we re prepared; being ethyl acetate extracts displayed the widest spectrum of anti-microorganisms at a minimum inhibitory concentration ≤0.095 mg/mL. The volatile composition of the fungi that displayed the highest (A. alternata) and the lowest (P. canescens) antimicrobial activity against yeasts revealed the presence of six volatiles, being the most abundant components (3-methyl-1-butanol and phenylethyl alcohol) ascribed with antimicrobial potentialities. Overall the results highlighted for the first time the antimicrobial potential of endophytic fungi from O. europaea and the possibility to be exploited for their antimicrobial agents. Graphical Abstract: [Figure not available: see fulltext.]This work is funded by FEDER funds through COMPETE (Programa Operacional Factores de Competitividade) and by national funds by FCT (Fundação para a Ciência e a Tecnologia) in the framework of the project “EndoBio—Isolation and screening of endophytic fungi for biological control of olive against Colletotrichum acutatum and Verticillium dahliae” (PTDC/ AGR-PRO/4354/2012).info:eu-repo/semantics/publishedVersio