A REVIEW ON MICROBIAL ENDOPHYTES FROM PLANTS: A TREASURE SEARCH FOR BIOLOGICALLY ACTIVE METABOLITES

Abstract

Microbial endophytes normally reside asymptomatically in the tissues of higher plants and act as source of original organic metabolites. In recent years, a great deal of information on the role of endophytes in host plants has been collected. Many important chemotherapeutics from endophytic metabolites could be used in medicine, agriculture and industry. With the intention to provide studies on endophytic microbes, this review focuses on the role of endophytes with respect to production of anticancer, antimicrobial, antioxidant and other biologically important compounds. The main topics addressed are plant-endophyte relationship, potential in drug discovery, host-endophyte relationship, diversity, distribution and natural products from endophytic microbes.

Headnote

ABSTRACT

Microbial endophytes normally reside asymptomatically in the tissues of higher plants and act as source of original organic metabolites. In recent years, a great deal of information on the role of endophytes in host plants has been collected. Many important chemotherapeutics from endophytic metabolites could be used in medicine, agriculture and industry. With the intention to provide studies on endophytic microbes, this review focuses on the role of endophytes with respect to production of anticancer, antimicrobial, antioxidant and other biologically important compounds. The main topics addressed are plant-endophyte relationship, potential in drug discovery, host-endophyte relationship, diversity, distribution and natural products from endophytic microbes.

KEY WORDS: Endophytes, anticancer, antimicrobial, antioxidation, secondary metabolites

INTRODUCTION

The word endophyte is derived from Greek "endo'>< "endon' meaning within, and "phyte'>< "phyton' meaning plant. The word "endophyte" was introduced by de Bary and was for some time applied to all "organisms occurring within plant tissues" (de Bary, 1866) or "all organisms inhabiting plant organs that at some time in their life, can colonize in internal plant tissues without causing apparent harm to the host" (Petrini, 1991). An endophyte by definition is one which resides in the tissues beneath the epidermal cell layers and causes no apparent harm to the host or fungi (Schulz and Boyle, 2005).

Generally several hundred endophyte species can be isolated from a single plant (Tan and Zou, 2001). Mostly Ascomycetes, Deutromycetes, and Basidiomyctes classess of fungi are reported as endophytic fungi. The class and species of fungi depends upon the host plants. Recent studies suggested that endophtytic fungi are not host specific and generally have widespread host range. Earlier studies lead to the conclusion that fungal endophytes are ubiquitous in plant species (Huang et al., 2008; Wu et al., 2006). Numerous reports infer that endophytic actinomycetes play roles in plant protection against pathogens and their metabolic products have influence on plant growth and physiology (Katznelson and Cole, 1965; Strobel and Daisy, 2003). The fungi like mycorrhizae are symbiotic associations in between fungi and roots of majority of plants. The external hyphae of mycorrhizae spread out in to soil surrounding the infected root tips, and as a result mycorrhizal fungi reside only partly inside the plant tissues. In this way, they are different from typical endophytes. Arnold et al., 2007 explored the difficulty of endophytes versus mycorrhizae and exemplify that the mycorrhizae found in roots are mostly different in taxonomic composition to those endophytes found in leaves. On one hand, endophytes can produce analogous or the same biologically active constituents as its host, such as an endophytic fungus producing taxol (Strobel et al., 1993).

Many important chemotherapeutics are either microbial metabolites or their semisynthetic derivatives. Investigating the metabolites of endophytes can boost the chance of finding novel compounds so; an intensifying stream of attention is being directed to the endophytes and biomass can be accumulated by large scale fermentation (Tan and Zou, 2001). This review aims to provide an overview of the endophytic natural products, along with potential applications particularly in the area of agriculture, medicinal industry and biological diversity with respect to microbial endophytes.

The plant endophyte relationship

The host-endophyte relationship is supposed to be complex and different from host to host and microbe to microbe. The fungus passes from one generation to next through the seeds (Boursnell, 1950; Bultman and Murphy, 2000). The fungus enters the seedling from the seed and spreads through out, enters new tissues as they arise for this plant. Germination and subsequent development of the seedling depends on the presence of the fungus, devoid of it the plant ceases to grow beyond certain stages. During the fall, the plant digests the swollen, hyphae of the fungus that are found in the roots, and obviously benefits nutritionally from the microbe. The relationship is truly mutalistic because the fungus must obtain nourishment from the plant since it does not have contact with the soil. Endophytes that inhabit foraging grasses e.g rye grasses, do not leave their plant host and can only reproduce by invading seed tissue of the plant (Stone et al., 2000).

Endophytes could be involved in pathogenecity of the host plants. The endophyte population in abnormally developed plant tissues, such as in galls and cysts are often quite different from healthy secretions (Stone et al., 2000). Environmental conditions such as soil temperature and humidity etc.would also are expected to affect the nature and the population of endophytes (Hata et al., 1998). Plants in unique environments that fight to compete with other living organisms or that need as much resistance as possible to survive, are probable candidates to host endophytes, which generate secondary metabolites that will assist the plants (Strobel et al., 2004). Many researchers hold that plants growing in tropical forest rainforest where competition for light and nutrient is intense, are most likely to host the greatest number of bioactive endophytes. Several studies note that endophytes from tropical regions produced significantly more bioactive secondary metabolites than those from temperate parts of the world (Bills et al., 2002).

Most of the innovation of surfeit of microbes for applications that span a wide range of efficacy in medicine, agriculture and industrial area is currently useful. However, considerable work has also been carried out on a variety of different plants example Musa acuminata, Glycine max, Sorgum bicolour, Triticum aestivum, Zea mays, Agropyron elongatum, Sorghastrum nutans, Sweet potato, Ocimum sanctum, Ocimum bacilicum, Leucas aspera and Azadirachta indica. (Wipornpan et al., 2001; Khan et al., 2010; Banerjee et al., 2009; Kharwar et al.,2008; Kumaresan et al., 2001) Endophytic microbes are the source of natural products, for optimizing the search for new bioactive secondary metabolites. It is also relevant to consider that,

i. The secondary metabolites synthesis may correspond with its respective ecological niche.

OR

ii. Continual metabolic interaction between endophytes and plant may enhance the synthesis of secondary metabolites.

Studies have proved that they have the capacity to produce toxins in response to infection that benefits the host plants (Stone et al., 2000). Unlike the plant host, many endophytes are able to survive under quite extreme and inhospitable conditions. In one study, hyphae within stored mycorrhizal roots survived for six years in dry soil (Stone et al., 2000; Strobel et al., 2004) and endophytes can be extracted from plant samples long after the plant tissues has died.

Endophytes and their potential in drug discovery

Endophytic microbes from medicinal plants are good source of functional metabolites (Tejesvi et al., 2007; Bailey et al., 2006). Endophyte infections have been found to alter pattern of gene expression in the host plant (Baily et al., 2006). Endophytes from Angiosperms as well as Gymnosperms have been studied for presence of novel secondary metabolites. The natural products produced by endophytes have vast range of bioactivities, representing a vast reservoir offering an enormous potential for exploitation in medicinal, agricultural and industrial uses (Tan and Zou, 2001). Crude extracts from culture broth of endophytes found to show antibacterial, antifungal, antiviral, anti- inflammatory and antitumor activities (Silva et al., 2007). Therefore endophytes open up new areas for the biotechnological exploitations.

Host endophyte relationship and effect on metabolites production

Microorganisms are likely to harbor metabolic pathways that lead to the production of novel secondary metabolites. Many of the important secondary metabolites have been extracted and characterized from endophytic microbes (Tan and Zou, 2001), which includes alkaloids, steroids, terpenoids, peptides, polyketones, flavenoids, quinols and phenols. In addition, natural products also often serve as lead structures whose activity can be enhanced by exploitation through synthetic chemistry (Strobel and Daisy, 2003). Endophytes are able to increase host fitness and competitive abilitity, by increasing nutritional uptake, resistance to seed predators, seed germination success, tolerance to heavy metals, high salinity and good growth rate through biochemical pathways such as phytohormone indole acetic acid (IAA) from fungal endophytes Acremonium coenophialum, Aureobasidium pullulans, Epicoccum purpurascens and Collectotrichum sp along with IAA, cytokinins were also produced by an endophytic Hypoxylon serpens (Tan and Zou, 2001). Plants provide spatial arrangement, shelter, nutrients and distribution to the next generation of microbes (Rudgers, 2000). Plant may provide vital compounds for the completion of the life cycle of the endophytes (Strobel, 2002). Current research suggested that endophytes and plant genotypic combinations together with environmental conditions are an important source of variation in endophyte host interactions (Faeth and Fagan, 2002). Many factors such as season, age, environment and location may contribute and influence the biology of endophyte (Strobel and Daisy, 2003). Endophytes derive nutrients from the plant without killing host, endophytic microbes such as Phomopsis, Phoma, Colletotrichum and Phyllosticta have wide host range and found to colonize numerous taxonomically distinct plants (Murali et al., 2006; Sieber, 2007) developing adaptations to overcome different types of host defence.

Endophyte infection affects the concentration of abscisic acid in leaves of drought stressed grasses and this helps in the recovery of endophytes infected plant in water deficient conditions also. Endophytic microbes residing in the host tissue some time turn in to a pathogen in response to some environmental signal (Hendry et al., 2002). Such a change in the nature of the endophytes would also result in a change in its metabolite profile (Suryanarayanan and Murali, 2006). Endophytic microbes associated with traditionally used medicinal plants particularly of the tropics could be a rich source of functional metabolites (Tejesvi et al., 2007).

Diversity and distribution of microorganisms recovered as endophytes

There are some major points represented with respect to diversity and distribution of endophytes as follows i. Individual endophytes can switch symbiotic lifestyles and the result of symbiosis is influenced by host genotypes ii. Mutalistic benefits conferred by endophytes are also influenced by plant genotypes iii. The host range of endophytes is inadequately defined and which includes both monocot and dicot species and iv. Endophyte's host plant describes adaptive symbiosis. Some endophytes have evolved with a high degree of suppleness to enter between genetically distinct plant species which provides endophytes an option to develop habitat range. Endophytic microbes can have intense effects on plant ecology, their fitness and are able to produce number of bioactive agents. The fossil proof shows that fungal symbionts have been associated with plants from the Ordovician period of approximately 400 million years ago, when plants first became established on land (Redecker et al., 2000), migrating from aquatic to terrestrial habitats. There are two major classes of fungal symbionts associated with internal plant tissues such as

i. Fungal endophytes residing entirely within host plants and associated with roots, stems, leaves, and flowers.

ii. Mycorrhizal fungi that are residing only in roots but extend out into the rhizosphere.

In count to this, fungal endophytes also are divided into two classes:

i. A comparatively minute number of fastidious species limited to a few monocot host plants (Clay and Schardl, 2002).

ii. A huge number of tractable species with broad host ranges, together with monocots and eudicots (Stone, 2000).

Considerable research have been done in class I endophytes as compared to class II endophytes, corresponding largest group of fungal symbionts. This is because the class II endophytes have only been elucidated in recent times and shown to be responsible for the adaptation of some plants to high-stress environments (Suryanarayanan and Murali, 2006). Endophytic fungi may express different symbiotic lifestyles in response to the host genotypes and environmental factors. Lifestyle expression of endophytes is a post colonization phenomenon which involves biochemical and genetic communications between endophytic microbes and host. Basically grass species, have been entirely studied in relation to their endophytic biology (Tan and Zou, 2001). Clavicipitaceous endophytes represents Class I and are small number of phylogenetically related Clavicipitaceous species which are fastidious in culture and also limited to some cool and warm seasonal grasses, (Stone et al., 2004). Transmission of these class I endophytes is mostly vertical, with maternal plants passing fungi on to offspring by means of the seed infections (Leuchtman, 2003). Class II endophyte generally comprises diverse species, all of which in general are members of the Dikarya (Ascomycota or Basidiomycota) having ability to give habitat specific stress tolerance to host plants.The main established hypothesis says that Clavicipitaceous endophytes are defensive mutualists of host grasses and play role during their evolution (Tanaka et al., 2005). Class III endophytes are basically distinguished on the basis of their occurrence and horizontal transmission, including vascular, nonvascular plants, some woody and herbaceous angiosperms in tropical forest and antarctic plant communities. These endophytes are especially known for their huge diversity within individual host tissues, plants and also populations. Class IV endophytes contains darkly melanized septa and they are restricted to plant roots. Generally these are Ascomycetous fungi conidial or sterile and forming melanized structures and also found in non mycorrhizal plants from antarctic, arctic, tropical ecosystems and temperate zones. Diversity of endophytic microbes shows to protect plants from the herbivores and is responsible for the production of novel secondary metabolites. Fungal endophytes those vertically transmitted are sexual and transmit via fungal hyphae penetrating the hosts' seeds for e.g Neotyphodium, these fungi are frequently mutualistic and on the contrary, endophytes transmitting horizontally are sexual and transmit via spores which can be spread by wind and insect vectors also. The endophytic microbes possibly adopt the same strategy as that of plant pathogenic fungi in order to enter the host plant (Sieber, 2007).

Research emphasize that endophytes are usually not host specific, single endophyte can have wide host range. Same microbe isolated from different tissue or part of the same host plant differs in their abilities for utilization of different substances, endophytic organisms associated with plants are varied and complex. Subsequent identification of potential genes provides evidence of specific pathway for known alkaloids synthesis by endophytes (Tanaka et al., 2005). Consequently if endophytes can produce the same bioactive compounds as their host plants this would reduce the need to harvest slow growing rare plants and also help to preserve the worlds diminishing biodiversity.

Plant growth promoting endophytes

Endophytes show numerous direct and indirect mechanisms to promote plant growth and health. Direct plant growth promoting mechanisms from endophytic suppression of the production of stress ethylene by 1- aminocyclopropane-1-carboxylate (ACC) deaminase activity (Dell'Amico et al., 2005) and alteration of sugar sensing mechanisms in plants. Non reducing disaccharide such as trehalose is main storage carbohydrate of bacteria; it is also produced in plants but in lesser extent as compaire to sucrose. This sugar thought to play a vital role in plants for controlling their partitioning of carbon into cell wall biomass (Ramon and Rolland, 2007). Alteration in biosynthesis and metabolism of trehalose also increase tolerance to drought, salt, and cold. Therefore several endophytic bacteria from poplar tree were able to metabolize trehalose for example Plasmodiophora brassicase. Plant-associated bacteria benefits plant by preventing the growth of pathogens through, antibiosis (Zhang et al., 2004). Plant-growth-promoting endophytic bacteria were isolated from Brachiaria hybrid CIAT 36062 and introduced into Brachiaria hybrid cv. Mulato, positive for nif H gene sequences and inoculated Mulato plants showed higher chlorophyll and total nitrogen contents in leaves, DNA sequence analysis demonstrated that the nif H gene found were highly similar to Klebsiella pneumoniae and some other N2-fixing organisms identical to those of other N2-fixing bacteria. For this reason plant research area are now diverted to use endophytes in development of agriculture crops and forest regeneration.

Natural Products from Endophytes

The requirement for new antimicrobial agents generally, comes from the increasing resistance of pathogenic microbes towards antibiotics. Many microorganisms are known to acquire resistance to commonly used antimicrobial chemical compounds. So the interest in natural methods of pathogen control through new, eco-friendly agents has increased. The biologically active natural products from endophytes are excellent resources for medicine, agriculture and industry (Guo et al., 2008). About 51% of biologically active substances from fungal endophytes were previously unknown. Amines and amides are very common metabolite products from endophytes and have shown to be toxic to insects but not to mammals. Bioactive metabolites, such as steroids, terpenoids and diterpenes also are generated by endophytes. Endophyte also produces extracellular hydrolyases to establish a resistance mechanism against plant invasion which includes some of the extracellular enzymes like cellulases, proteinase, lipases and esterases. The actions of these enzymes found to support the hypothesis of co-evolution between endophytes and their hosts (Tan and Zou, 2001). Number of secondary metabolites produced by fungal endophytes is larger than that of any other endophytic microorganisms. Endophytic fungi are a promising source of novel compounds (Redecker et al., 2000).

Role of Endophytes in the discovery of anticancer agents

Endophytes hold main position in drug discovery as it has antibiotic, antiviral and anticancer properties, due to their ability to produce novel chemicals which can be used as drugs. Pacli taxel was first found in plants and later on reported from fungal endophyte. It is the first major group of anticancer agents which is produced by endophytes and now much research has been conducted on endophytes to determine its anticancer activity. Production of taxol was also done from endophytic fungi, Lasiodiplodia theobromae isolated from Morinda citrifolia with its cytotoxicity against human breast cancer cell line. Other important anticancer agents from the fungal endophytes were reported including camptothecin and several analogues (Redman et al., 2001) vincristine (Figure 1.Chemdraw) and podophyllotoxin. Subsequently one hundred anticancer compounds which belong to different chemical classes with activity against 45 different cell lines have been isolated from different fungal species belonging to different groups, out of which 57% were novel oranalogues of known compounds. Endophytic fungi was isolated and identified from Juniperus communis L. Horstmann, as a novel producer of deoxypodophyllotoxin (Kusari et al., 2009).

Secondary metabolites from endophytes as antibiotics

Plants with ethno botanical history are generally expected to be powerful source of endophytes producing active natural products. As more than 3000 diseases are clinically described today less than one third of these can be treated symptomatically. And even a less than that need needs new therapeutic agent with infectious diseases control (Strobel and Daisy, 2003). Tan and Zou in recent times isolated secondary metabolites of endophytes are synthesizing via variety of metabolic pathways (Tan and Zou, 2001) e.g polyketide, isoprenoid or amino acid derivation and belonging to different structural groups such as phenols, isocoumarins steroids, xanthones, perylene derivatives, depsipetides quinines, furandiones, terpenoids, and cytochalasines. Fungus Podospora Sp endophytic from the plant Laggera alata (Asteraceae) shows presence of xanthones sterigmatocystin (Figure 2.Chemdraw). Also chaetoglobosin A and rhizotonic acid were reported from endophytic Chaetomium globosum in Maytenus hookeri and Rhizoctonia Sp. in cynodon dactylon correspondingly to be active against the gastric ulcer. Altersetin from endophytic Alternaria Sp shows potent activity against pathogenic Gram positive bacteria.

Fungal genus Cinnamomum zeylanicum found to be producing extremely bioactive volatile organic compounds (VOCs). Endophytic Muscodor albus produces a mixture of VOCs consists primarily of various alcohols, acids, esters, ketones and lipids. Cryptocandin A, an antifungal lipopeptide was isolated from endophytic Cryptosporiopsis quercina containing a number of unusual hydroxylated amino acids and 3 hydroxy-4- hydroxymethyl proline which founds to be active against some fungal pathogens like Candida albicans, Trichophyton Sp., Sclerotinia Sclerotiorum and Botrytis cinerea (Wipornpan et al., 2001). The endophytic Chloridium Sp. from A.indica produces Javanicin (Figure 3. Chemdraw) which is highly active against Pseudomonas Spp. (Tejesvi et al., 2007). A tetramic acid cryptocin (Figure 4. Chemdraw) was obtained from endophytic microbe, strong activity against Pyricularia oryzae plant pathogenic fungi. Endophytic fungus initiate production of Ambillic acid which is highly functionalized cyclohexenone with strong antifungal activity. A strain of Pestalotiopsis microspora, isolated from the tree Torreya taxifolia, produces a compound pestaloside having antifungal activity. Pestalotiopsis jester is an endophytic fungi produces the extremely functionalized cyclohexenone epoxides jesterone and hydroxy jesterone, exhibiting excellent antifungal activities against a variety pathogenic fungi of plants. Fungal endophyte isolated from Acalypha indica species shows potent antibacterial activity against human pathogenic bacteria such as Bacillus subtilis, Klebsiella pneumoniae and Staphylococcus aureus. The mechanism of antibiosis includes production of antibiotic compounds, bioactive volatile organic compounds (VOCs) and some enzymes (Ownley et al., 2010). Fungal endophyte Phomopsis Sp YM 311483 produces four new ten membered lactones activite against Aspergillus niger, Botrytis cinere and Fusarium spendophytic (Strobel, 2002). Jesterone synthesis was reported with potent antifungal activity from endophytic Pestalotiopsis jesteri. Endophytic fungi isolated from Rhizophora mucronata, Avicenna officialis and Avicenna marina and their ethyl acetate extract showed maximum antibacterial activity against bacterial pathogens and anticancer activity for Hep2 and MCF7 cell line In Vitro.

Endophytic Gram positive bacteria like Bacillus Sp have also been isolated from cotton, cucumber root and citrus plant. Coronamycin characterize a complex peptide antibiotic with activities against pythiaceaus fungi, human fungal pathogen Cryptococcus neoformans and also against the malarial parasite Plasmodium falciparum was produced by a Verticillate Streptomyces spendophyte from an epiphytic vine Monstera Sp (Ezra et al., 2004). During the isolation of endophytes, actinomycetes generally appeared much later than endophytic bacteria and fungi and are also able to produce various metabolites. Streptomyces Sp. NRRL30566, from a fern- leaved grevillea (Grevillea pteridifolia) tree, reported to produce original kakadumycin chemically related to echinomycin. Biologically dynamic species of Streptomyces were isolated from species of Nothofagus and some other plants from the southern reaches Patagonia. Having activity against plant pathogens, like Pythium ultimum, Sclerotinia sclerotiorum, Mycosphaere llafijiensis and Rhizoctonia solani (Wu et al., 2007; Castillo et al., 2007).

Secondary metabolites from endophytes as antiviral agent

Endophytes have also been studied for their antiviral activity, the emergence of multiresistance against existing drugs, and high cost of current therapies as well as the AIDS associated opportunistic infections, such as Cytomegalo virus and Polyoma virus needs essential antiviral agent. Cytonic acid A and B were recognized as human cytomegalo virus protease inhibitors from endophytic fungus Cytonaema Sp. isolated from Quercus Sp. (Guo et al., 2008). A novel quinine related metabolites xanthoviridicatins E and F was also produced by an endophytic Penicillium chrysogenum able to inhibit the cleavage reaction of HIV-1 integrase

Some antioxidant compounds produced by endophytes

Free radicals are atoms causing damage to body cells and harmful to our immune system leading to many of degenerative diseases. Antioxidant donates electron to free radicals and converts them to harmless molecules, protecting cells from oxidative damage aging and various diseases. Antioxidant are habitually produced many endophytes. Pestacin and Isopestacin were produced by Pestalotiopsis microspora from host Terminalia morobensis (Strobel, 2002). About 12 endophytes from Trachelospermum jasminoides were assayed for more potent free radicals scavenging activities using 1, 1, diphenyl,-2-picrylhyrazyl (DPPH) and hydroxyl radicals assay. Endophytes from medicinal plants are main resources for antioxidant metabolites helps to study relationship between total antioxidant capacity (TAC) and total phenolic content (TPC). The antioxidant capacities of the endophytes were significantly correlated with their total phenolic contents, suggesting that phenolics are the key antioxidant constituents of endophytic microbes. Metabolites produced by fungal endophyte can be a good source of novel natural antioxidant compounds (Wu et al., 2007).

Secondary metabolites from endophytes as antimycotic agents

Fungal infections are now becoming difficult problem as a result of the bigger numbers organ transplants patients with weakened immume systems so required new antimycotic agent to contest these problems (Strobel, 2002). A unique peptide antimycotic, Cryptocandin A was isolated from Cryptosporiopsis quercina, endophyte of medicinal plant Tripterigeum wilfordii.

Secondary metabolites from endophytes with further intersting Pharmacological activities

Compounds with immuno-suppressive activities were obtained from endophytic fungi such as subglutinols A and B which are non cytotoxic diterpene pyrones from Fusarium subglutinans, endophyte from Triptergium wilfordii. Aurasperone A (Figure 5. Chemdraw) from endophytic Aspergillus niger isolated from Cynodon dactylon is xanthine oxidase inhibitor. 3 Hydroxypropionic acid was isolated from endophytic fungi showing nematicidal activity against the plant-parasitic nematode such as Meloidogyne incognita with the Lithal dose 50 values of 12.5-15µg/ml. This was the first report of 3-hydroxypropionic acid from endophytic fungi with the nematicidal activity (Michael et al., 2004). Endophytes do produce secondary metabolites when placed in culture, however, the temperature ,the composition of the medium and the degree of aeration will affect the amount and kind of compound that are produced by an endophytic fungus (Strobel et al., 2004). The host endophyte interaction provides nutrients and shelter for endophytes, which in substitute improve plant growth and health. Many endophytic bacteria are closely related to environmental and clinical isolates whose genomes have been or are in the process of being sequenced.

Plant endophyte interactions affect metabolite production

Plants have been viewed as a major source of new lead compounds for drug discovery, attention has more recently turned to endophytes as these microorganisms have great potential as sources for new bioactive compounds (Jalgaonwala and Mahajan, 2011). This may be the case because endophytes may have developed close biological associations with and inside their host, leading to the production of high number and diversity of classes of biological activities. Thus they represent an under-utilized resource in the search for new compounds. Studies of these organisms indicate that they are prolific producers of compounds that can be exploited as both agrochemical and medicinal agents (Jalgaonwala and Mahajan, 2011; Jalgaonwala et al., 2011).

Jalgaonwala and Mahajan, (2011) made investigation on different tissues of selected fifteen indigenous medicinal plants such as Aloe vera, Curcuma longa, Azadirachta indica, Coriandrum sativam, Eucalyptus globules, Hibiscus rosa sinensis, Ixora coccinea, Murrayo koenginii, Musa paradiasica, Ocimum sanctum, Pongamia glabra, Sphaeranthus indicus, Vinca rosea, Vitex nigundo and Withania somniphera. The research provided by Jalgaonwala and Mahajan (2011) evidence that isolated endophytes such as bacteria, fungi and actinomycetes are capable to survive inside medicinal plants. The endophytic diversity from selected plant species was rich. About 50% of test isolates exhibit potent antimicrobial activity and metabolite were partially characterized with attempts to identify potent microbes.The search for new compounds is certainly of equal importance however, has been the discovery that some endophytes produce compounds that have been exclusively isolated from higher plants. Described below in Table 1 are some examples of bioactive products from endophytic fungi and their potential in the pharmaceutical and agrochemical arenas.

CONCLUSION

Endophytes comprise a diverse group of species existing in several ecosystems. In present report, we summarise the study of endophytes, their diversity and bioprospecting. Endophytic microbes are omnipresent within all identified plants in various bionetworks, but the geographical differences in their diversity, composition, host and tissue specificity have not been well documented. A powerful and good sequencing technology will make the global assessment of endophyte diversity. The above discussed novel bioactive compounds are only a few examples of what has been found after the isolation and culturing of individual endophytic fungi followed by purification and characterization of some of their natural products. The prospects of finding new drugs that may be affective for treating newly developing diseases in humans, plants and animals are great their applications in industry agriculture may also be discovered among the novel products produced by endophytes.

ACKNOWLEDGMENT

We are thankful to principal Moolji Jaitha College, Jalgaon for providing laboratory as well as library facilities to complete the research work.

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Cite this article:

Ruby Jalgaonwala, Raghunath Mahajan (2014), A REVIEW ON MICROBIAL ENDOPHYTES FROM PLANTS: A TREASURE SEARCH FOR BIOLOGICALLY ACTIVE METABOLITES, Global J Res. Med. Plants & Indigen. Med., Volume 3(6): 263-277

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