ENDOPHYTIC ACTINOMYCETES AND THEIR ROLE IN PROTECTION

Transcription

1 Fatema Jariwala, Ravi Ranjan* Dept. of Biotechnology, Shree M & N Virani Science College, Rajkot, Gujarat raviranjan@vsc.edu.in ENDOPHYTIC ACTINOMYCETES AND THEIR ROLE IN PROTECTION endophytic actinomycetes. Not only to the plants; they even produces numerous bioactive compounds which are of human benefit. Keywords: Endophytic actinomycetes, bioactive compounds, phytopathogenic Introduction Abstract Actinomycetes are one of the most attractive sources of antibiotics and other biologically active substances of high commercial value. It accounts roughly for two-thirds of the total known antibiotics isolated from these gram positive, branched spores bearing filamentous Actinomycetes are best known for their ability to produce antibiotics and are gram positive bacteria which comprise a group of branching unicellular microorganisms. They produce branching mycelium which may be of two kind s viz., substrate mycelium and aerial group of Eubacteria with controversial bacto- mycelium. Among actinomycetes, the fungoid morphology. Among the streptomycetes are the dominant. The actinomycetes, Streptomyces spp. has been the non streptomycetes are called rare most abundant sources of all types of actinomycetes, comprising approximately 100 antibiotics. Screening and isolation of genera [1]. Actinomycetes are saprophytes that promising strains of actinomycetes with play a significant role in the breakdown of potential antibiotics is still a thrust area of organic matter into more readily as similable research and it is suggested that the nutrients. They are also well-known producers explorations of materials from new areas and habitats have a pivotal role to play in the search for new microbes and novel metabolites and is urgent to counter the threats posed by the fast emerging phenomenon of antibiotic of vast array of secondary metabolites, many of which have useful applicationsin human and veterinary medicine and agriculture. Over the last 75 years, numerous strains of actinomycetes have been isolated from various resistance.including the endophytic substrates collected worldwide and havebeen actinomycetes in the race of search along the coaxed to express their extraordinary actinomycetes, endophytes have been biosynthetic capacity in culture. Soil, which demonstrated to improve and promote growth of host plants as well as to reduce disease symptoms caused by plant pathogens and/or various environmental stresses. The low stress tolerance of axenic plants is commonly believed to result partly from the absence of contains the greatest density and diversity of actinomycetes, has been the predominant and conventional source of actinomycete strains. More recently, however, scientists have found that other terrestrial substrates, such as leaf litter and plants, are potential sources of 73

2 actinomycete biodiversity. Endophytic potent sources of endophytes producing active actinomycetes, which can be recovered from healthy, surface-disinfected plant tissues, are known to produce a variety of bioactive natural products than other plants. Endophytic actinomycetes are, particularly, considered as potential sources of bioactive compounds and metabolites with antibiotic, enzymatic,and various novel compounds. Previous plant growth-promoting or -inhibiting investigations of Endophytic actinomycetes activities. There is evidence that actinomycetes are fairly prevalent in crop or garden plants, such as wheat, maize, and Chinese cabbage, from the Egyptian medicinal plants indicated high antimicrobial activities and highlighted their importance as candidates for further and some of these isolates have been shown to investigation in the biocontrol of produce bioactivity or have potential as phytopathogens. The ability of Endophytic biocontrolagents, especially against actinomycetes to inhibit phytopathogenic phytopathogenic fungi[2]. fungi is mainly by production of bioactive compounds, such as antibiotics and cell wall Characteristics of actinomycetes: degrading enzymes. In addition, endophytes 1.It reproduced via spores. 2. Hyphal growth is are known to compete phytopathogens for followed by fragmentation and release of spores. 3. Conidia- spores produces asexually on aerial filaments called sporophores. 4. Shape and arrangement of sporophores help in nutrients. They were also reported to hold the ability of triggering plant induced systemic resistance (ISR). [4] The endophytes may provide protection and survival conditions to identification of actynomycete taxa. 5. their host plant by reducing a plethora of Predominantly soil bacteria. 6. Good at substances which, once isolated and degrading recalcitrant compounds such as characterized, may also have potential for use chitin and cellulose. 7. Often active at higher industry, agriculture, and medicine. ph which is contrast to fungi who may dominate at lower ph. 8. Gives soil the earthy smell [3]. Approximately plant species growing in unexplored area on the earth are host to one or more endophytes, and the presence of bio diverse endophytes in huge number plays an Endophytic actinomycetes: Endophytes are microorganisms that, for the whole part of their life history, live inside plant tissues without causing immediate overt negative effects as a result of these long hand associations, Endophytic microorganisms and plants have developed good information transfer, leading to the hypothesis that plants with an ethanobotanical history are more important role on ecosystems with greatest biodiversity, for instance, the tropical and temperate rainforests, which are extensively found in Brazil and possess almost 20% of its biotechnological source. Considering that only a small amount of endophytes have been studied, recently, several research groups have been motivated to evaluate and elucidate the potential of these microorganisms applied on 74

3 biotechnological processes focusing on the production of bioactive compounds. The the major antioxidant constituents of the endophytes. production of bioactive Substances by endophytesis independent directly evolution related of to the these Antimicrobial compounds: Metabolites bearing antibiotic activity can be microorganisms, which may have incorporated defined as low-molecular-weight organic genetic information from higher plants, natural substances made by microorganisms allowing them to better adapt to plant host and that are active at low concentrations against carry out some functions such as protection other microorganisms. Endophytes are from pathogens, insects, and grazing animals. Endophytes are chemical synthesizer inside plants, in other words, they play a role as a selection system for microbes to produce bioactive substances with low toxicity toward believed to carry out a resistance mechanism to overcome pathogenic invasion by producing secondary metabolites. So far, studies reported a large number of antimicrobial compounds isolated from endophytes, belonging to several higher organisms. Bioactive natural structural classes like alkaloids, peptides, compounds produced by endophytes have steroids, terpenoids, phenols, quinines, and been promising potential usefulness in safety flavonoids. The discovery of novel and human health concerns. antimicrobial metabolites from endophytes is an important alternative to overcome the Antibiotics Natural antioxidants are commonly found in increasing levels of drug resistance by plant and human pathogens, the insufficient number medicinal plants, vegetables, and fruits. of effective antibiotics against diverse However, it has been reported that metabolites from endophytes can be a potential source of novel natural antioxidants. Liu and co-workers evaluated the antioxidant activity of an bacterial species, and few new antimicrobial agents in development, probably due to relatively unfavourable returns on investment. The antimicrobialcompounds can be used not endophytic Xylariasp. isolated from the only as drugs by humankind but also as food medicinal plant Ginkgo biloba.the results preservatives in the control of food collected indicated that the methanol extract exhibited strong antioxidant capacity due to the presence of phenolics and flavonoids compounds among 41 identified compounds. spoilageand food-borne diseases, a serious concern in the world foodchain. One strain F0010 of the endophytic fungus Xylariasp from biesholophylla was characterized as a Huang and coworkers investigatedthe producer of griseofulvin (C17H17ClO6), a antioxidant capacities of endophytic fungal spirobenzofuran antifungalantibiotic agent cultures of medicinal Chinese plants and its correlation to their total phenolic contents. They suggested that the phenolic content were used for the treatment of human andveterinary animalsmycotic diseases [72]. They evaluated andreported high antifungal activity in vivo 75

4 and in vitro of heendophyte-produced griseofulvin against plant pathogenicfungi, controlling effectively the development of various foodcrops. Anticancerous compounds: There are some evidences that bioactive compounds produced by endophytes could be alternative approaches for discovery of novel Antioxidants: Antioxidants have been considered promising therapy for prevention and treatment of ROSlinked diseases as cancer, cardiovascular drugs, since many natural products from plants, microorganisms, and marine sources were identified as anticancer agents. The anticancer properties of several secondary disease, atherosclerosis, hypertension, metabolites from endophytes have been ischemia/reperfusion injury, diabetes mellitus, investigated recently. Following, some neurodegenerative diseases (Alzheimer and Parkinson diseases), rheumatoid arthritis, and ageing. Many antioxidant compounds possess examples of the potential of endophytes on the production of anticancer agents are cited. The diterpenoid Taxol (also known in the antiantiatherosclerotic,antitumor, inflammatory, antimutagenic, literature as paclitaxel) have generated more attention and interest than any other new drug anticarcinogenic, antibacterial, or antiviral activities in higher or lower level. Natural antioxidants are commonly found in medicina lplants, vegetables, and fruits. However, it has since its discovery, possibly due to its unique mode of action compared to other anticancer agents. This compound interferes with the multiplication of cancer cells, reducing or been reported that metabolites from interrupting their growth and spreading. FDA endophytes can be a potential source of novel natural antioxidants. Liu and co-workers evaluated the antioxidant activity of an endophytic Xylaria sp. Isolated from the medicinal plant Ginkgo biloba. The results collected indicated that the methanol extract exhibited strong antioxidant capacity due to the presence of phenolics and flavonoids compounds among 41identified compounds. (Food and Drug Administration) has approved Taxol for the treatment of advanced breast cancer, lung cancer, and refractory ovarian cancer. Taxol (C47H51NO14) was firstly isolated from the bark of trees belonging to Taxus family (Taxusbrevifolia), its most common source. Nevertheless, these trees are rare, slow growing, and produce small amount of Taxol, which explain its high price in the Huang and coworkers investigated the market when obtained by this natural source. antioxidant capacities of endophytic fungal cultures of medicinal Chinese plants and its correlation to their total phenolic contents. They suggested that the phenolic content were Besides, in the context of environmental degradation, the use of plant source as unique option have limited the supply of this drug due to the destructive collection of yew trees. the major antioxidant constituents of the Several reports about Taxol anticancer endophytes. properties were published since its discovery, 76

5 as well as other sources for production of Taxol have been investigated in the last seedlings, suggesting that this strain might release some type of rooting- promoting plant decade.the isolation of Taxol-producing hormone(s). This strain certainly gives a great endophyte Taxomycesandreanae has provided practical advantage to shorten the an alternative approach to obtain a cheaper and acclimatization period of tissue-cultured more available product via microorganism fermentation. [5] seedlings in warm and humid environments, thereby decreasing the disease-infection risk of the seedlings. Endophytic Actinomycetes and their metabolites that affect plant s life Endophytes colonizing inside plants usually Enzymes: Some Streptomyces strains are known to get nutrition and protection from the host produce hydrolytic cell wall-degrading plants. In return, they confer profoundly enhanced fitness to the host plants by producing a variety of bioactive metabolites. Growth stimulation of plants by endophytes enzymes such as cellulases, hemicellulases, chitinases, amylases and glucanases50 53). Other strains are also known for their ability to produce enzymes that degrade the lignin, can be a consequence of nitrogen fixation or cellulose and hemicellulose of higher the production of phytohormones, biocontrol of phytopathogens through production of plants54 56). However, these strains were isolated from soil, sediments or rhizosphere. antibiotics or siderophores, nutrient Only a few strains producing hydrolytic competition, and induction of systemic disease enzymes were of plant origin. resistance. Some of these metabolites directly affect physiology of the host plants but others do so indirectly by affecting the microbe Streptosporangium sp. isolated from leaves of maize was reported to produce glucoamylase, which is expected to improve industrial population by antibiosis and/or competition. processes of starch degradation57). Minamiyama et al.25) demonstrated by Plant growth promoters: Recently, Meguro et al.45) reported a strain of electron microscopy that leaf surface of rhododendron was degraded by enzymes Streptomyces sp. MBR-52 that accelerated released from contacting hyphae of emergence and elongation of plant Streptomyces adventitious roots. When tissue-cultured seedlings of rhododendron were treated with Agricultural use of endophytic MBR-52 in flasks, this strain colonized within actinomycetes: the seedlings and survived there even after their transplanting in soil. Emergence of Use of endophytic actinomycetes to produce disease resistant tissue-cultured seedlings adventitious roots was prominently accelerated in the MBR-52-treated tissue-cultured 77

6 Enhanced drought-tolerance of tissue-cultured seedlings by endophytic colonization of actinomycetes [6] References: [4] Moussa Heba E. Ahmed Dewedar et al. [1] Sivakumar K Actinomycetes. Ph.D Characterization of endophytic thesis. Annamalai University actinomycetes from wild Egyptian plants as [2] Janso Jeffery E. and Carter Guy T antagonists to some phytopathogenic fungi. Potential of Phylogenetically Unique [5] Mariana Recco Pimentel, Ana paula Endophytic Actinomycetes from Tropical Dionisio et al The use of endophytes to Plants. Applied and environmental obtain bioactive compounds and their microbiology. 76 (13): application in biotransformation process. [3] Awad Hassan M. Kamal y. I. El-shahed SAGE and Abd El-Monaem M.el-nakkadi [6] Sachiko Hasegawa, Tomio Nishimura et al. Isolation screening and identification of newly Endophytic actinomycetes and their isolated soil Streptomyces (Streptomyces sp. interaction with host plants. NRC-35) for β- Lactamase Inhibitor Actinomycetologica. 20 (2): 72-8Egyptian Production. World applied science journal. 7 journal of natural toxins. 8 (1,2): (5):