Introduction the natural product with a therapeutic effect.

Introduction

Bacterial
and fungal infections are very common problem in human population. The chemical
synthetic drugs which are used to remove this medical problem may have several
side effects to us1. Thus the lead
molecule of the effective drug can be synthesised from the natural product with
a therapeutic effect. It is expected that drug from the natural compound will
be renewable, naturally eco-friendly and easily obtainable2. Plants are the
potential source of novel bioactive compounds. The micro-organisms associated
within the plants, i.e , endophytes may also produce biologically active
compounds similar to their host plant3 in direct or
indirect manner.

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Endophytes, by definition, are -“microbes that colonize living,
internal tissues of plants without causing any immediate overt negative
effects”4. Studies have shown that, more or less every
plant species examined have atleast one endohyte species5. There is a mutual relationship between the
host plant and their endophytes. Endophytes may produce secondary metabolites
which prevent growth of pathogen or may kill the pathogen and in return plant
gives shelter and nutrition to these endophytes. In support of this idea many
antimicrobial, antifungal compounds are isolated from the endophytes6. There are many reports in the discovery of
natural compounds with potential antimicrobial activity from fungal endophytes7.

Therefore the aim of this review is to take a look
on recent research on antimicrobial metabolites and antibiotics produced from
endophytic bacteria.

Ecology
and Diversity of Endophytic Bacteria

Endophytes are found within most of plant species5. Endophytes may
present herbaceous to woody plant. Endophytes enter into the host tissue
through root zone or aerial zone8. It has been
reported that they may enter through stomata, lenticels9 or through
wounds10.  Within the host plant endophytes reside
either intercellularly or intracellularly. They may also reside within the
vascular tissues of their host plant11.

From a single plant species different
types of endophytes can be isolated. It may also possible from various plant
species a wide variety of endophytes are reported9. The diversity
of 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.

 

 

Screening
of Antimicrobial Metabolites

Three basic and major
steps are involved in the screening of antimicrobial metabolites from
endophytes. 1st one is selection of plant material. It is very
important steps because selection of plants provides the opportunity to isolate
endophytes 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 criteria
may be selection of traditional medicinal plants and isolation of endophytes
from them15. The second
step is preliminary screening of antimicrobial
activity . Crude extract of endophytes are tested for their antimicrobial activity
by agar cup method or paper disc diffusion method16.Then active subtances of crude extract can be separated by Thin
Layer Chromatography technique and other chromatographic techniques17. The third step is development of antibiotics from the
potent metabolites.The general procedure of separation of antimicrobial
compounds is given below:

Selrction
of plant material

 

Isolation of endophytic
bacteria through surface sterilization

 

Preliminary screening
for antimicrobial activity from the crude extracts of endophytes

 

Separation of active
compounds through chromatographic techniques

 

Development of antibiotics from the potent metabolites

 

 

 

 

 

 

 

 

 

Table 1 – List of some potent bacterial endophytes
with 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