Molecular Approaches to Screen Bioactive Compounds from Endophytic Fungi

Abstract

Endophytic fungi are capable of producing plant associated metabolites and their analogs with therapeutic value. In order to identify the potential endophytic isolates producing bioactive compounds, one need to screen all isolated endophytes, which may run into hundreds. Isolation of endophytic fungi is relatively a simple process; but screening of the isolated fungi for required metabolite production is a cumbersome process. Endophytic fungi producing plant associated metabolites may contain genes involved in the entire biosynthetic pathway(s). Therefore, ascertaining the presence of key enzymes of a particular biosynthetic pathway could serve as a molecular marker for screening of these endophytes to produce that metabolite. In absence of entire biosynthetic pathways in endophytic fungi, plant genes associated with that metabolic pathway could serve as markers. This review focuses on the impact of molecular approaches to screen the endophytic fungi for the production of bioactive compounds. An attempt has been made on screening of anticancer compounds like taxol (paclitaxel), podophyllotoxin, and camptothecin using molecular markers. The advantages of molecular approaches over conventional methods to screen endophytic fungi and also identification of endophytic fungi are discussed.

Keywords: bioactive compounds; camptothecin; endophytic fungi; molecular markers; paclitaxel; podophyllotoxin; secondary metabolites.

Figure 1

Schematic representation of biosynthetic pathway leading to taxol along with corresponding enzymes catalyzing steps in taxol biosynthesis [TS: taxadiene synthase; TAT: taxe-4(20), 11(12)-diene-5α-ol-)-acetyltransferase; DBAT: 10-deacetylbaccatin III 10-O-acetyl-transferase; BAPT: baccatin III 13–O-(3-amino-phenylpropanoyl) transferase].

Figure 2

Alignment of deduced amino acid sequences of BAPT from various species of Taxus and endophytic fungal isolates showing high level of sequence homology.

Figure 3

Biosynthetic pathway of podophyllotoxin along with newly proposed steps (A), the steps with dotted arrows indicate the gaps that needs to be worked out in this pathway. From Lau and Sattely (2015). Reprinted with permission from AAAS.

Figure 4

Biosynthesis of strictosidine and its subsequent conversion to important alkaloids including anti-cancer compounds. Reproduced from Panjikar et al. (2012) with permission of The Royal Society of Chemistry.

Figure 5

Schematic diagram showing identification of the cultivable and non-cultivable endophytic fungal communities from a plant source. Reprinted from Sun and Guo (2012). with permission from Mycological Society of China.

Figure 6

Phylogenetic analysis of different endophytic fungi isolated from Western Ghats of India using parsimony analysis. Parsimony bootstrap support (BS) and Bayesian PP values >50% are given at the internodes (BS/PP). Reprinted from Suryanarayanan et al. (2011). with permission from Elsevier.