VOLUME 12 (Supplement)

Diversity and bioactivities of mangrove fungal endophytes from Leyte and Samar, Philippines

Mangrove fungal endophytes (MFEs) are known to be viable sources of metabolites with potential antibacterial and cytotoxic properties. In this study, 73 fungal endophytes were isolated from 4 mangrove hosts, namely, Sonneratia alba J. Smith., Rhizophora mucronata Lamk., Aegiceras floridum Roemer & Schultes, and Avecinnia marina (Forssk.) Vierh., collected in Leyte and Samar, Eastern Philippines. Among these mangrove hosts, R. mucronata from Samar had the highest MFE diversity and species richness. Differences in fungal species composition were also noted between the same host mangroves collected from different sites. Although fungal endophytes are known to exhibit host specificity, in this study, similar species of mangroves are actually hosts to different fungal endophytes. The MFEs were characterized as belonging to 24 morphospecies. Identities of the representative strains of the 24 morphospecies were then confirmed by multigene analysis, i.e., ITS (internal transcribed spacer region), CAL (partial calmodulin gene), HIS (partial histone H3 gene), GAPDH (partial glyceraldehyde-3-phosphate dehydrogenase gene), TEF (partial translation elongation factor 1-alpha gene), TUB (partial beta-tubulin gene), ApMAT (Apn2/MAT locus), and ACT (partial actin gene). Of these, 16 MFEs were mass-produced to extract secondary metabolites for antibacterial and cytotoxic tests. Culture extracts of Pestalotiopsis adusta were most effective against Pseudomonas aeruginosa with a MIC (minimum inhibitory concentration) of 80 µg/ml. Twelve MFEs grown under stationary conditions and 15 MFEs grown under agitated conditions showed an inhibitory concentration (IC50) of less than 500 µg/ml against the K562 myelogenous leukemia cell line. Of these, Xylaria cubensis grown under stationary conditions exhibited the lowest IC50 of 99.35±19.5 µg/ml. This study paves the way for the first report of the MFEs from the central part of the Philippines and the discovery of potential metabolites which can be explored for pharmaceutical applications.