IntroductionBacterialand fungal infections are very common problem in human population. The chemicalsynthetic drugs which are used to remove this medical problem may have severalside effects to us1. Thus the leadmolecule of the effective drug can be synthesised from the natural product witha therapeutic effect. It is expected that drug from the natural compound willbe renewable, naturally eco-friendly and easily obtainable2. Plants are thepotential source of novel bioactive compounds.
The micro-organisms associatedwithin the plants, i.e , endophytes may also produce biologically activecompounds similar to their host plant3 in direct orindirect manner.Endophytes, by definition, are -“microbes that colonize living,internal tissues of plants without causing any immediate overt negativeeffects”4. Studies have shown that, more or less everyplant species examined have atleast one endohyte species5.
There is a mutual relationship between thehost plant and their endophytes. Endophytes may produce secondary metaboliteswhich prevent growth of pathogen or may kill the pathogen and in return plantgives shelter and nutrition to these endophytes. In support of this idea manyantimicrobial, antifungal compounds are isolated from the endophytes6.
There are many reports in the discovery ofnatural compounds with potential antimicrobial activity from fungal endophytes7.Therefore the aim of this review is to take a lookon recent research on antimicrobial metabolites and antibiotics produced fromendophytic bacteria.Ecologyand Diversity of Endophytic BacteriaEndophytes are found within most of plant species5.
Endophytes maypresent herbaceous to woody plant. Endophytes enter into the host tissuethrough root zone or aerial zone8. It has beenreported that they may enter through stomata, lenticels9 or throughwounds10. Within the host plant endophytes resideeither intercellularly or intracellularly. They may also reside within thevascular tissues of their host plant11.
From a single plant species differenttypes of endophytes can be isolated. It may also possible from various plantspecies a wide variety of endophytes are reported9. The diversityof endophytes include Gram positive as well as Gram negative bacteria like Achromobacter,Acinetobacter, Agrobacterium, Bacillus, Brevibacterium,Burkholderia,Chromobacterium, Curtobacterium, Enterobacter, Kocuria,Lysinibacillus, Methylobacterium, Microbacterium,Paneibacillus, Pantoea,Phyllobacterium, Pseudomonas, Rahnella, Rhodanobacter, Stenotrophomonas,Streptomyces, Xanthomonas etc12,13. Screeningof Antimicrobial MetabolitesThree basic and majorsteps are involved in the screening of antimicrobial metabolites fromendophytes. 1st one is selection of plant material. It is veryimportant steps because selection of plants provides the opportunity to isolateendophytes with ability to produce novel anti- microbial metabolites. So,plants can be selected from special ecological environment. For example,mangrove plants can be selected and endophytes can be isolated from them14.
Other criteriamay be selection of traditional medicinal plants and isolation of endophytesfrom them15. The secondstep is preliminary screening of antimicrobialactivity . Crude extract of endophytes are tested for their antimicrobial activityby agar cup method or paper disc diffusion method16.Then active subtances of crude extract can be separated by ThinLayer Chromatography technique and other chromatographic techniques17. The third step is development of antibiotics from thepotent metabolites.The general procedure of separation of antimicrobialcompounds is given below:Selrctionof plant material Isolation of endophyticbacteria through surface sterilization Preliminary screeningfor antimicrobial activity from the crude extracts of endophytes Separation of activecompounds through chromatographic techniques Development of antibiotics from the potent metabolites Table 1 – List of some potent bacterial endophyteswith their antimicrobial property are given below: Sl No Host Plant Potent Endophyte Activity Shown Test Organism Reference No 1 Panax ginseng Paenibacillus polymyxa GS01, Bacillus sp.
GS07, and Pseudomonas poae JA01 Antifungal Phytopathogenic fungi 2 T. grandiflora Polyalthia sp. Mapania sp. Streptomyces fulvoviolaceus, Streptomyces coelicolor, Streptomyces caelestis Antifungal Phytopathogenic fungi 3 Scutellaria baicalensis Georgi Bacillus amyloliquefaciens Antibacterial, Antifungal Phytopathogenic, food-borne pathogenic and spoilage bacteria and fungi 4 Panax notoginseng Bacillus amyloliquefaciens subsp. plantarum , Bacillus methylotrophicus Antifungal Phytopathogenic fungi and nematode 5 Azadirachta indica A. Juss.
Streptomyces sp., Nocardia sp. Antibacterial, Antifungal Phytopathogenic fungi, Human pathogenic bacteria and fungus 6 Plectranthus tenuiflorus Bacillus sp. Pseudomonas sp. Antibacterial, Antifungal Human pathogenic bacteria and fungus 7 Wheat Bacillus subtilis Antifungal Phytopathogenic fungi 8 Anthurium B.
amyloliquefaciens Antibacterial Phytopatogenic bacteria 9 Platycodon grandiflorum Bacillus licheniformis, Bacillus pumilus, Bacillus sp. Antibacterial, Antifungal Phytopathogenic fungi and anti-human food-borne pathogenic organisms 10 Artemisia annua Streptomyces Antibacterial, Antifungal pathogenic bacteria, yeast and fungal phytopathogens 11 Centella asiatica Bacillus subtilis, Pseudomonas fluorescens Antifungal Phytopathogenic fungi 12 Panicum virgatum L. Bacillus subtilis, C. flaccumfaciens, Ps. Fluorescens, P. ananatis Antifungal Phytopathogenic fungi 13 Raphanus sativus L Enterobacter sp.
, B. subtilis Antibacterial, Antifungal Phytopathogenic fungi, Human pathogenic bacteria 14 Memecylon edule , Tinospora cordifolia, Phyllodium pulchellum and Dipterocarpus tuberculatus Bacillus amyloliquefaciens Antibacterial, Antifungal Human pathogenic bacteria and fungus 15 S. lavandulifolia, H. scabrum, R. pulcher Bacillus sp. Antibacterial, Antifungal Human pathogenic bacteria and saprophytic fungi 16 Aloe chinensis Paenibacillus species Antibacterial, Antifungal Pathogenic bacteria and fungi 17 Epimedium brevicornu Maxim. Phyllobacterium myrsinacearum Antibacterial, Antifungal Phytopathogenic fungi and phytopathogenic bacterium 18 11 mangrove halophytic plants Bacillus Thuringiensis and Bacillus pumilus Antibacterial Shrimp pathogens 19 Kandelia candel Streptomyces sp. Antibacterial Several pathogenic bacteria 20 Codonopsis lanceolata Bacillus pumilus B.
subtilis B. licheniformis Antifungal Phytopathogenic fungi 21 Polygonum cuspidatum Streptomyces sp. Antifungal Pathogenic fungi 22 Manihot esculenta Paenibacillus sp. Antifungal Phytopathogenic fungus 23 Bruguiera gymnorrhiza Rhizophora stylosa Kandelia candel Bacillus amyloliquefaciens Antibacterial, Antifungal Phytopathogenic fungi and phytopathogenic bacteria 24 Monstera sp. Streptomyces sp. Antifungal, Antimalarial Pythiaceous fungi and the human fungal pathogen, malarial parasite 25 Piper nigrum L P.
aeruginosa, P. putida and B. megaterium Antifungal Phytopathogenic fungus 26 Huperzia serrata Burkholderia sp. Antifungal Phytopathogenic fungi 27 300 plants from upper Amazonian Rainforests Streptomyces sp.
Micromonospora sp. Amycolatopsis sp. Antibacterial, Antifungal Range of potential fungal and bacterial pathogens 28 Lycopersicon esculentum Streptomyces sp., Microbispora sp.
, Micromonospora sp. and Nocardia sp. Antibacterial, Antifungal Phytopathogenic fungi and phytopathogenic bacteria