A. Elavarasi and M. Kalaiselvam*

Centre of Advanced Study in Marine Biology

Faculty of Marine Sciences

 Annamalai University

Parangipettai, India.

 email - kalaifms@gmail.com*

Introduction

The ocean is considered to be a source of potential drugs. India is consecrated with a more than 8000 kms of coastline, possessing over 2 million sqkms of Exclusive Economic Zone (EEZ). Indian coastline has every type of marine habitats like inter-tidal, rocky, muddy and sandy shores, coral reefs and mangrove forest. However, the potential of this domain as the basis for new biotechnologies remains largely unexplored. A few selected research institutes in India are engaged in the exploration of life saving drug from marine sources. Many International research institutes and pharma based companies have recognized the significances of this area and acknowledged the importance of establishing interdisciplinary research centers focusing on marine natural products. Similar efforts should be made in India in order to explore biotechnological potential of our country’s untapped marine biodiversity.

Marine natural products have attracted the attention of biologists and chemists over for the last five decades. Several of the compounds isolated from marine source exhibit biological activity. Most of these molecules are still in preclinical or early clinical development from marine associated microbes. In recent years, marine natural product bio-prospecting has yielded a considerable number of drug candidates.

Endophytic fungi are now recognized as a new and relatively unexplored source of bioactive compounds. Chiefly mangrove endophytic fungi have rich metabolites because symbiotic associations between fungi and photosynthetic organisms are both ancient and ubiquitous protecting host against various aggressions. Endophytes are growing intercellularly and asymptomatically within living tissues establishing mutual relationship with the host plant.  Most of the endophytic fungi have a wide range of plant host diversity. This paper reviews the biodiversity and novel metabolites production of endophytic fungi of mangrove.

Diversity of mangrove endophytic fungi

Endophytic fungi are reported from plants growing in various environments including tropic, temperate, xerophytes and aquatic. Marine fungi do not form a traditional taxonomic grouping (Raghukumar, 2008), but rather form an ecological grouping. Within the marine fungi there are two sub-divisions are found i.e. obligate and facultative marine fungi (de Vita-Marques et al., 2008). According to Raghukumar (2008), 800 species of obligate marine fungi have been reported, comprising mostly of Ascomycetes and only 56 species have been discovered for facultative marine fungi (de Vita-Marques et al., 2008).

A wide range of parasitic and saprophytic fungi have been reported from mangrove environment either living on the tissue, as epiphytes, rather than within.  But few studies have investigated the endophytes from mangrove. Yang et al. (2006) reported 290 strains of endophytic fungi obtained from Fugong in Fujian Province, China. They reported that the dominant genera were Penicillium sp., Alternaria sp., Dothiorell sp and non-sporulating groups. Several studies on fungi associated with mangrove detritus have been published. There are a few studies on the endophytic fungi of mangrove plants and most of them are confined to endophytes from Pichavaram mangrove (Kumaresan and Suryanarayanan, 2002). 

Bioactive compounds from mangrove endophytic fungi

Complex interactions between the host and the endophyte, such as the provision of various types of defensive substances (secondary metabolites) by the endophyte, have led to further research of these organisms. Some of these endophytes produce bioactive substances that are products of the host-microbial interactions. The most well-known example being that of taxol, a multibillion dollar anti-cancer compound produced in yew plant Taxus brevifolia by the terrestrial endophytic fungus Taxomyces andreanae (Strobel, 2002).

Endophytic fungus Dothiorella sp. isolated from mangrove plant of Avicennia marina have antimicrobial   and cytotoxicity effect against human epidermal carcinoma of oral cavity, KB cell line (carcinoma cell line) and human Burkitt’s lymphoma (Xu et al., 2005).

Similarly, Pestalotiopsis sp. isolated from the leaves of Rhizophora mucronata, produced various bioactive compounds such as pestalotiopyrones, pestalotiopisorin, pestalotiollides A, pestalotiopin A, and four amides namely pestalotiopamides, nigrosporapyrone, 2- anhydromevalonic acid, and ρ- hydroxyl benzaldehyde.

Mangrove endophytic fungi Phomopsis sp. from Hibiscus tiliaceus derived a new substance namely A-seco-oleane-type triterpenes. The structurally related A-seco-oleane in mangrove endophytes may play an importantrole in protecting the host plant against environmental infections. Cytosporones, coumarins and alkaloid compounds derived from endophytic fungi of Pestalotiopsis sp isolated from Rhizophora mucronata. Isoflavones isolated from mangrove endophytic fungi Fusarium sp. and subsequently, mangrove endophytic fungi Penicillium chermesinum exhibited cytotoxicity activity against cancer cell lines. Conversely, toxin and acids such as paeciloxocins were isolated from the mangrove fungus Paecilomyces sp. Paeciloxocin A exhibited strong cytotoxicity against the hepG2 cell line (Chen et al., 2010).   In addition Xia et al. (2008) reported two new acids with a known compound, purpactin A were isolated from mangrove endophytic fungus (No. ZZF13). 

Conclusion

Diversity of mangrove endophytic fungi with its unique physiological adaptations to the extreme marine environment provides a fruitful source for the discovery of new life saving drug. Although substantial progress has been made in identifying novel drug from the marine sources, great endeavors are still needed to explore these molecules for clinical applications.

References

Chen, G., She, Z., Wen, L., Yan, C., Cai, J.  and Mu, L. (2010) Two new paeciloxocins from a mangrove endophytic fungus Paecilomyces sp. Russian Chemical Bulletin, International Edition. 59(8):1656 – 1659.

de Vita-Marques, A. M., Lira, S. P., Berlinck, R. G. S., Seleghim, M. H. R., Sponchiado, S. R. R.  and Tauk-Tornisielo, S. M. (2008). A multi-screening approach for marine-derived fungal metabolites and the isolation of cyclodepsipeptides from Beauveria felina. Quim. Nova. 31: 1099 - 1103.

Kumaresan, V. and Suryanarayanan, T. S.  (2002) Endophyte assemblage in young, mature and senescent leaves of Rhizophora apiculata: evidence for the role of endophytes in mangrove litter degradation. Fungal Diversity. 9: 81 - 91.

Raghukumar, C. (2008) Marine fungal biotechnology: an ecological perspective. Fungal Divers. 31: 19 – 35. 

Strobel, G. A. (2002) Rainforest endophytes and bioactive products. Critical Review in Biotechnology. 22: 315 – 333. 

Xia, X. K., Yang, L.G., She, Z. G., Shao, C. L.,  Huang, Z. J., Liu, F.,  Lin, Y.C.  and Zhou. S. N.  (2008) Two new acids from mangrove endophytic fungus (no. ZZF13). Chemistry of Natural Compounds. 44(4): 416 – 418. 

Xu, Q. Y., Huang, Y. J., Zheng, Z. H. and Song, S. Y. (2005) Purification, elucidation and activities study of cytosporone B. Journal of Xiamen University (Natural Science). 44(3): 425 - 428 (in chinese).