Isolamento e seleção de fungos endofíticos produtores de compostos bioativos associados às plantas do gênero Rheedia

Abstract

The majority of natural compounds in the world has not been tested yet, due to vast biodiversity available. Plants of the genus Rheedia can be sources of endophytic fungi producers of bioactive compounds because it presented chemical and pharmacological properties well described in the literature. Endophytic fungi deserve particularly consideration because they include microorganisms with high species diversity and consequently, high chemistry diversity and uniqueness of molecules with biological activities proven. This study aimed isolate endophytic fungi from Rheedia brasiliensis leaves, selecting the most outstanding and testing their ability to produce bioactive metabolites with antimicrobial, antioxidant and antiproliferative activity. In all, 245 fragments of leaves of R. brasiliensis were analyzed with isolation of 154 fungi (isolation frequency of 62.86%). Two fungi were selected, through the antimicrobial screening, for more advanced studies: the first one was Paraconiothyrium sp. P83F4/1, which belongs to a new genus recently described and it may be important in the production of new molecules of interest, and, the second was Colletotrichum gloeosporioides P67F1/1, which presents a historical of metabolites and bioactive molecules that are outlined by the scientific community. The first part of this study evaluated biological properties of extract obtained from submerged fermentation into czapek broth of the Paraconiothyrium sp. P83F4/1 endophytic fungus. So, this extract was tested for its capacity to produce bioactive compounds with antimicrobial, antioxidant and antiproliferative properties of interest. The strains of Staphylococcus aureus and Escherichia coli were susceptible to fungal extract tested, with greater emphasis against S. aureus, whose minimum inhibitory concentration (MIC) values ​​were 500-1000 µg/mL. Using the method of DPPH (1,1-diphenyl-2-picril-hydrazyl radical), Paraconiothyrium sp. P83F4/1 extract showed scavenging capacity (average sequestrant capacity + standard deviation), at 90 ppm, of 58.92+0.024 (%), and was significantly higher (p<0.05) than commercial standard Butyl Hidroxi Toluene (BHT), of 39.52+0.095 (%). The Paraconiothyrium sp. P83F4/1 extract also stood out for selectivity on HaCat cells (human keratinocytes), important in diseases such as psoriasis, with GI50 value of 0.95 mg/mL (mean log GI50 = -0.02). These results indicate extract powerfull of the Paraconiothyrium sp. P83F4/1 and stimulate continuation of studies, with elucidating of compounds and deep knowledge about action mechanisms involved in such activities. The second part of this study aimed to analyze the biological potential of crude wheat bran extract and demonstrate its influence on fermentation processes using the C. gloeosporioides P67F1/1 to obtain bioactive compounds. The dichloromethane extract of wheat bran presented biological activities equal or higher than the fungal extract. For antimicrobial assay, both extracts showed MIC of 250-500 µg/mL. The scavenging capacity (%) of extracts, revealed by the DPPH, showed values ​​(average sequestrant capacity + standard deviation): of 17.7+0.037 (wheat bran) and 10.56+0.004 (fungus), with the bran extract significantly (p <0.05) better than the fungal extract. For the antiproliferative assay, the wheat bran crude extract showed weak activity for the most part of tumor lines tested (25.34<GI50 (µg/mL)<47.75, 1.40<average of logGI50<1.68). On the other hand, the fungus extract was inactive for all tested cell panel (GI50>250 µg/mL, average of logGI50>2.40), according to National Cancer Institute criteria. According to results obtained, we verified that wheat bran was not an inert fermentation substrate. So, for some fermentation processes is necessary more care to use it, in order to avoid influences of (direct and/or indirect) chemical composition on activities expected for the extracts on analysis, originated from fungal fermentation processes.