Insights into the Bioprospecting of the Endophytic Fungi of the Medicinal Plant Palicourea rigida Kunth (Rubiaceae): Detailed Biological Activities

Abstract

A multitude of plants from the Brazilian savanna are known for their medicinal properties. Many plants contain endophytic fungi, which lead to the production of bioactive compounds by both the fungi and their hosts. This study investigated the bioprospecting of endophytic fungi recovered from the leaves of Palicourea rigida, a native medicinal plant of the Brazilian savanna. Four fungal taxa (Colletotrichum sp. SXS649, Pestalotiopsis sp. SXS650, the order Botryosphaeriales SXS651, and Diaporthe sp. SXS652) were recovered. The phenolic, flavonoid, extracellular degrading enzymes (amylase, cellulase, protease, and tannase) and antioxidant activity of these taxa were determined. Evaluation of the antimicrobial activity showed that the Botryosphaeriales SXS651 extract displays a minimum inhibitory concentration (MIC) of 23.20 mg mL^-1 against Staphylococcus epidermidis and Pseudomonas aeruginosa, and the Diaporthe sp. SXS652 extract exhibited an MIC of 27.00 mg mL^-1 against Escherichia coli. The Colletotrichum sp. SXS649 isolate inhibited tumors in potato discs by 69% at a concentration of 9.70 mg mL^-1. All isolates had potential bioremediation criteria against soil contaminated with soybean oil, as proved by a high percentage of germination of Lactuca sativa and a reduction in phytotoxicity. Furthermore, the taxa under investigation demonstrated antagonistic action to phytopathogenic fungi, namely, Aspergillus niger, Inonotus rickii, Pestalotiopsis mangiferae, and Coniophora puteana, with an inhibition range between 34.2% and 76.9%. The preliminary toxicity assessment showed that all isolates possessed an LC50 of less than 100 mg mL^-1 to the microcrustacean Artemia salina. These results indicate that the endophytic fungi of the Brazilian savanna are promising candidates for biotechnological and industrial applications and, in agricultural applications, for the biological control of phytopathogenic fungi.

Keywords: bioprospecting; biotechnological potential; endophytic fungi; medicinal plants; natural products; secondary metabolites.

Figure 1

Geographic location of the UEG Ecological Reserve (REC-UEG), Anápolis, Goiás, Brazil and specimens of Palicourea rigida sampled.

Figure 2

HPLC chromatograms of extracts of the endophytic fungi Colletotrichum sp. SXS649, Pestalotiopsis sp. SXS650, Botryosphaeriales SXS651, and Diaporthe sp. SXS652 isolates from P. rigida Kunth. Values correspond to the average of 3 repetitions.

Figure 3

Enzymatic profile of the endophytic fungi Colletotrichum sp. SXS649, Pestalotiopsis sp. SXS650, Botryosphaeriales SXS651, and Diaporthe sp. SXS652 isolates from P. rigida Kunth. (a) Enzyme index (IE). Values correspond to the average of 3 repetitions: (b) Cultures in specific media showing the substrate degradation halo as indicative of enzymatic activity.

Figure 4

Antitumor activity in potato discs of extracts of the endophytic fungi Colletotrichum sp. SXS649, Pestalotiopsis sp. SXS650, Botryosphaeriales SXS651, and Diaporthe sp. SXS652 isolates from P. rigida Kunth. (a) Inhibition rate against the concentration of fungal extracts. Values correspond to the average of 3 repetitions; and (b) Potato disc tumors treated with Colletotrichum sp. SXS649.

Figure 4

Antitumor activity in potato discs of extracts of the endophytic fungi Colletotrichum sp. SXS649, Pestalotiopsis sp. SXS650, Botryosphaeriales SXS651, and Diaporthe sp. SXS652 isolates from P. rigida Kunth. (a) Inhibition rate against the concentration of fungal extracts. Values correspond to the average of 3 repetitions; and (b) Potato disc tumors treated with Colletotrichum sp. SXS649.

Figure 5

Paired culture test of endophytic fungi isolated from P. rigida Kunth against phytopathogenic fungi at 14 days of incubation. The plates arranged in the upper row correspond to the control and in the lower row to the test. (A): Above C. puteana SXS623 and below the same fungus × Diaporthe sp. SXS652 (PI 76.93%). (B): Above A. niger SXS635 and below the same fungus × Pestalotiopsis sp. SXS650 (PI 59.25%). (C): Above I. rickii SXS37 and below the same fungus × Pestalotiopsis sp. SXS650 (PI 57.14%).