Colony forming Unit (CFU)
Reference
Alfalfa xylem tis-
6.0 × 10 3 to 4.3 × 104 per g
Gagné et al., 1987
sue
Cotton xylem tissue 1 × 102 to 11 × 103 per g
Misaghi and Donndelinger, 1990
Sugar beet tissue
3.3 × 103 to 7.0 × 105 per g
Jacobs et al., 1985
Potato tubers
0 to 1.6 × 104 per g
De Boer and Copeman, 1974
Table 3: Endophytic strains reported in between 2001-2007 (Sudhir, 2014)
Source
No of endophytes
Reference
Indian sugarcane
81 endophytic bacterial strains Suman et al., 2001
agronomic crop species
853 endophytic bacteria
Lodewyckx et al., 2002
prairie plant species
27 endophytes
Zinniel et al., 2002
Daucus carota
360 endophytic strains of Surette et al., 2003
and Agrobacterium
Pseudomonas and Staphylo-
coccus
soybean
35 endophytic bacteria
Hung et al., 2007
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Bacterial Endophytes as Bio fertilizers and Bio control Agents… Audipudi et al.
endophytes also influence the growth of
adjustment, stomatal regulation, modifi-
plant directly by the production of plant
cation of root morphology, enhanced up-
growth promoting traits such as IAA pro-
take of minerals and alteration of nitrogen
duction, Phosphate solubilization, sidero-
accumulation and metabolism. Adhikari
phore production, ammonia production,
et al.( 2001) reported that endophytic bac-
nitrogen fixation antagonism against phy-
terial strains are potential in controlling
topathogens and indirectly by induced
the seedling disease of rice and promote
systemic resistance (ISR). Endophytic
growth in rice. Application of endophytic
bacteria colonize an ecological niche sim-
bacterial strains significantly increased
ilar to that of phytopathogens, which
the growth parameters viz., pseudostem
makes them suitable as biocontrol agents
height, girth, number of leaves and physi-
(Berg et al., 2005a). Endophytic microor-
ological parameters viz., chlorophyll sta-
ganisms control plant pathogens (Sturz &
bility index, stomatal resistance and tran-
Matheson, 1996; Duijff et al., 1997;
spiration in banana plants both under
Krishnamurthy
&
Gnanamanickam,
greenhouse and field conditions (Harish,
1997), insects (Azevedo et al., 2000) and
2005).
nematodes (Hallmann et al., 1997, 1998)
through endophyte-mediated de novo syn-
4.1. IAA production
thesis of novel compounds and antifungal
According to earlier studies IAA
metabolites. Endophytes can also acceler-
production by endophytes can vary
ate seedling emergence, promote plant
among different species and isolates and
establishment under adverse conditions
it is also influenced by culture condition,
(Chanway, 1997) and enhance plant
growth stage and substrate availability.
growth (Bent & Chanway, 1998).
Out of 65 endophytes of soybean, 15 iso-
Bacterial endophytes stimulate the
lates were positive for IAA production
growth of host plant by nitrogen fixation,
produced more than 25 μg/ml of IAA and
enhancement in the availability of miner-
Acetobacter diazotrophicus and Her-
als and the production of phytohormones
baspirillum seropedicae found to produce
(Hurek et al. 2002; Iniguez et al. 2004;
IAA in chemically defined culture media.
Sevilla et al. 2001). Endophyte mediated
Seven out of 10 endophytic isolates of
de novo synthesis of antifungal or anti-
Typha australis were positive for IAA
bacterial metabolites, siderophores and
production (Hung and Annapurna 2004;
competition for nutrients induce system-
Chen et al., 1998; Jha and Kumar, 2007).
atic resistance in the host to check the
Two bacterial endophytes of Capsicum
progress of disease (Sessitsch et al.
annuum L. also reported to show plant
2002a; Sturz et al. 2000).
growth promotion and defense against
phytopathogens along with IAA produc-
4. Endophytic bacteria as bio fertilizers
tion. Long et al. (2008) reported 1.1 to
154μg/ml of IAA production by the en-
Research has been revealed that
dophytic bacteria isolate from Solanum
endophyte increase plant growth through
nigrum. Gangawar and Kaur (2009) re-
the improved cycling of nutrients and
ported 15 endophytic isolates of sugar-
minerals such as phosphate solubilisation
cane produced 4 to 19.3 μg/ml of IAA.
(Verma et al., 2001; Wakelin et al.,
Chilli endophytes are observed to be more
2004), indole acetic acid production (Lee
potential in IAA production than sugar-
et al., 2004) production of siderophore
cane and similar to Solanum nigrum re-
(Costa and Loper, 1994) and supply of
ported (Sudhir 2014). Amrutha et al.
essential vitamins to plants (Pirttila et al.,
(2012) reported that Pseudomonas aure-
2004). Compant et al. (2005) reported
ginosa CEFR3, Bacillus sp CEFR19,
that endophytes also influence other ben-
Curtobacterium
oceanosedimentum
eficial effects of host include osmotic
AVSCE3 and Bacillus cereus AVSCE 5
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Bacterial Endophytes as Bio fertilizers and Bio control Agents… Audipudi et al.
isolated from different parts of chilli pro-
Pseudomonas spp. Isolated from Serbia
duced 23µg/ml, 21µg/ml, 111.5µg/ml
able to solubilize TCP (Stajković et al.,
and 125μg/ml of IAA, respectively. It
2011; Djuric et al., 2011; Josic et al.,
was much higher than that of found in
2012b). Amrutha et al. (2012) reported
other reports (Long et al. 2008).
that Pseudomonas aureginosa CEFR3
Harish et al., (2008) assessed the
(198ppm/ml),
Bacillus
sp
CEFR19
plant growth promotion efficacy of 45
(1354ppm/ml) isolated from ripened fruit
endophytic bacteria isolated from corm
and isolated from green fruit and Bacil-
and root of banana. 12 strains isolated
lus cereus AVSCE 5(137ppm/ml) isolat-
from gingseng plant, endophytic P. fluo-
ed from leaf of chilli are able to solubil-
rescens WCS365 as biocontrol s bacteria
ize inorganic phosphate efficiently. In-
isolated from Lycopersicon esculentum
crease in the yield of canola by endophyt-
produced significant amounts of IAA
ic Bacillus sp. was reported by de Freitas
(Thamizh Vendan et al., 2010, Patel et
et al. (1997). Sundara et al. (2002) report-
al., 2012). Three strains isolated from
ed that enhancement in available phos-
sugar beet roots produced indole-3-acetic
phorus and yield of sugarcane by applica-
acid (IAA) promote plant growth signifi-
tion endophytic bacteria. Pseudomonas
cantly increased plant height, fresh and
spp. are able to increase the growth and
dry weights and number of leaves per
phosphorus content of maize by endo-
plant (Long et al., 2008; Yingwu Shi et
phytes (Vyas and Gulatti, 2009).
al., 2009). Vetrivelkalai et al., 2010 also
reported significant enhancement in the
4.3. Siderophore
germination percentage, shoot and root
Researchers reported that endophytic
length and vigour index of bhendi seed-
fungal siderophore have lower affinity
lings by seed bacterization.
than bacteria to sequester iron and deprive
pathogenic fungi (Whipps, 2001; Loper
4.2. Phosphate solubilization
and Henkels 1999). Endophytic bacterial
Earlier reports revealed endophyt-
isolates associated with hyacinth and
ic bacteria also solubilize phosphate from
Genseng plants produce siderophore
organic or inorganic bound phosphates
(Jafra et al., 2009; Thamizh Vendan et
and type of organic acid produced during
al., 2010). Rajkumar et al., (2010) report-
phosphate solubilizaton depends on the
ed that the siderophore play a pivotal role
carbon source utilized as substrate. High-
in nitrogen fixation under iron deficiency.
est P solubilization has been observed
when glucose, sucrose or galactose has
4.4. Nitrogen fixation
been used as sole carbon source in the
According to earlier studies en-
medium (Khan et al., 2009; Park et al.,
dophytic bacteria better express their ni-
2010). Endophytic bacteria able to solu-
trogen fixation potential inside plant tis-
bilize inorganic phosphate and extracel-
sues due to the lower competition for nu-
lular tricalcium phosphate effectively in
trients and protection against high levels
presence of glucose (Kuklinsky - Sobral
of O2 present on the root surface. Many
et al., 2004; Long et al., 2008; Thamizh
diazotrophic bacteria are able to establish
Vendan et al., 2010; Patel et al., 2012).
a symbiotic relationship with plants for
Endophytic
Bacillus,
Pseudomonas,
biological nitrogen fixation (Robson et
Klebsiella and Acinetobacter are also re-
al., 1986; Chisnell et al., 1988; Dekas et
ported as potential phosphate solubilizers
al., 2009). Earlier studies reveled that en-
(Huang et al., 2010). Endophytic Bacillus
dophytic diazotrophs constitute only a
cereus and B. megaterium isolated of
small proportion of total endophytic bac-
Ginseng plant also showed significantly
teria include Azospirillum lipoferum,
high P solubilization (ThamizhVendan et
Klebsiella pnemoniae and Azorhizobium
al., 2010). Endophytic and rhizosphere
caulinadans (Schloter et al., 1994; Bar-
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Bacterial Endophytes as Bio fertilizers and Bio control Agents… Audipudi et al.
raquio et al,. 1997; Martínez et al., 2003).
and studied growth response of A. thali-
Unlike symbiotic diazotrophes, endophyt-
ana. Each strain showed significant vola-
ic bacteria are unable to form nodules.
tile-mediated plant growth modulation
Gluconacetobacter diazotrophicus was
and also reported that Burkholderia pyr-
identified as first N2-fixing endophytic
rocinia as significant plant growth-
bacteria associated with sugarcane stem
promoter. The volatiles indole, 1-hexanol
(Cavalcante and Dobereiner, 1988) and
and pentadecane promotes growth only
confirmed by other scientists in USA,
under stress conditions
UK, and Germany and two more N2-
fixing endophytes Herbaspirillum sero-
5. Endophytes as biological control
pedicae and H. rubrisubalbicans were
agents (BCA)
reported by Boddey et al., (1995). James
(2000) reported Herbaspirillum sp. as en-
Endophytes are potential biocon-
dophytic diazotroph in sugarcane and
trol agents like other biocontrol agents
rice. Azoarcus sp. in rice and Kallar grass
such as associative nitrogen fixing PGPB
and endophytic Klebsiella sp. Kp342
on sugarcane (Boddy, 2003) or Burkhold-
strain of wheat identified as nitrogen fix-
eria phytofirmans PsJN, non-symbiotic
ers (Iniguez et al., 2004). Silva-Froufe
endophytic bacteria (Sharma and Nowak,
(2009) reported Glucanoacetobacter dia-
1998) endophyte holds potential of BCA
zotrophicus as endophytic diazotrophic
may be due to self-perpetuating nature of
bacteria in sugarcane, sweet potato, and
endophytes inside the host by coloniza-
pineapple. Endophytic Bacillus species of
tion and being transfer to progeny (Bod-
soybean nodule showed potential N fixing
dy, 2003). According to Backman et al.
and reported to improve root growth and
(1997), the effectiveness of endophytes as
function, (Bai et al., 2002; Asis et al.,
biological control agents (BCA) is de-
2004; Matiru and Dakora, 2004). 23 en-
pendent on many factors. These factors
dophytic bacteria are identified as poten-
include: host specificity, the population
tial ammonia producers in chilli (Amrutha
dynamics, pattern of host colonization,
et al., 2012) and reported that Pseudomo-
ability to move within host tissues and the
nas, Curtobacterium and Bacillus sp iso-
ability to induce systemic resistance. Cer-
lated from chilli were found to be maxi-
tain endophytic bacteria trigger induced
mum producers of Ammonia.
systemic resistance (ISR) which is pheno-
typically similar to systemic-acquired re-
4.5. Volatile compounds
sistance (SAR). SAR develops when
Earlier literature reveled that en-
plants successfully activate their defense
dophytic bacteria can produce a wide
mechanism in response to primary infec-
range of volatiles. Biological function of
tion by a pathogen and induces a hyper-
most of these volatiles is not yet under-
sensitive reaction in the form of a local
stood. It is assumed that volatile com-
necrotic lesion of brown desiccated tissue
pounds involved in a number of processes
(van Loon et al., 1998). ISR is effective
including cell-cell signaling, inter-species
against different types of pathogens bu
signaling, promote plant growth and act
differs from SAR because in ISR the in-
as microbial inhibiting agents (Wheatley,
ducing bacterium does not cause visible
2002; Vesperman et al., 2007; Kai et al.,
symptoms on the host plant (van Loon et
2009). Ryu et al., (2003) reported that
al., 1998).
Bacillus sp. produce 2, 3 butanediol and
The first record of an endophyte
acetoin and promote plant growth in Ara-
affecting a plant disease was reported by
bidopsis thaliana. 38 volatile compounds
Shimanuki (1987) who showed that Phle-
were reported from rhizobacteria (Farag
um pratense plants infected with the
et al., 2006). Blom et al. (2011) screened
Epichloe typhina were resistant to the
42 strains in four different growth media
fungus Cladosporium phlei. In some cas-
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Bacterial Endophytes as Bio fertilizers and Bio control Agents… Audipudi et al.
es, endophytes also accelerate seedling
Serratia marcescens 90-166 reduced Cu-
emergence and promote plant establish-
cumber Mosaic Virus (CaMV) in toma-
ment under adverse conditions and en-
toes and cucumbers (Raupach et al.,
hance plant growth and development (Pil-
1996), anthracnose and Fusarium wilt in
lay and Nowak, 1997). Several endophyt-
cucumber (Liu et al., 1995).
ic bacterial species including Achromo-
Sixty one (61) endophytic bacteria
bacter sp., Acinetobacter baumannii, A.
isolated from potato stem tissues were
lwoffii, Alcaligenes, Moraxella sp., Alcal-
identified as effective biocontrol agents
igenes sp., Arthrobacter sp., Bacillus sp.,
against Clavibacter michiganensis subsp.
Burkholderia cepacia, Citrobacter freun-
Sepedonicus (Sturz et al., 1999). Bacillus
dii, Corynebacterium sp., Curtobacterium
mycoides BacJ and Bacillus pumilis 203-7
flaccumfaciens, Enterobacter cloacae, E.
isolates from different host plants sup-
aerogenes, Methylobacterium extorquens,
pressed Cercospora leaf spot in sugar
Pantoea agglomerans, Pseudomonas ae-
beet (Bargabus et al., 2002: 2004). Araujo
ruginosa, and Pseudomonas sp. isolated
et al. (2002) reported Curtobacterium
from the xylem of lemon roots ( Citrus
flaccumfaciens, citrus endophyte help
jambhiri) have been reported as antago-
citrus plants to better resist against the
nistic bacteria against root phytopatho-
pathogenic infection of Xylella fastidi-
gens (Araújo et al., 2001; Lima et al.,
osa. Endophytes isolated from potato
1994).
plants produce antibiotics and siderophore
Cabbage treated with endophytes
a