Colonization of the plant’s interior by bacteria generally starts with their establishment in the rhizosphere. The early events of this process such as recognition and chemotaxis have been extensively reviewed by Lugtenberg et al. (2001) and Lugtenberg and Kamilova (2009). They will not be covered here. Following rhizosphere colonization, bacteria attach to the rhizoplane, i. e. the root surface. A number of mutational studies showed that attachment of bacterial cells to the root is a crucial step for subsequent endophytic establishment. Several bacterial surface components can be involved in this process. For Azoarcus sp. BH72, an endophytic diazotroph of rice, type IV pili encoded by pilAB are required for attachment to the root surfaces (Dörr et al., 1998). A mutant impaired in the expression of pilAB fails to successfully colonize roots and shoots of rice plants (Reinhold-Hurek et al., 2006). The attachment of another diazotrophic endophyte, Herbaspirillum seropedicae, to root surfaces of maize depends on LPS (liposaccharide) (Balsanelli et al., 2010). A mutant strain with changed monosaccharide composition in the core domain of LPS showed a hundred-fold lower root adhesion and endophytic spreading compared to the wild type. A similar study showed that EPS (exopolysaccharide) is necessary for rhizoplane and endosphere colonization of rice plants by Gluconacetobacter diazotrophicus (Meneses et al., 2011). Since none of these mutant strains completely lost their ability for adhesion, it can be expected that other bacterial surface components are also involved in this process.
There is no information on Nepalese sweet potato endophytes. We isolated 243 endophyticbacteria belonging to 34 genera in six classes from 12 loca- tions of Nepal. Among them, the predominant classes were Bacilli and Gam- maproteobacteria. The principal component analysis revealed that the com- position of bacterial classes was unrelated to the environmental parameters of the sampling sites. Regarding their plantgrowthpromoting potentials, 57% of the strains demonstrated indole-3-acetic acid (IAA) producing ability while 5% strains had nitrogen fixing gene ( nifH ) and acetylene reduction assay (ARA) activity. The representative strains in all six classes showed antagonis- tic effect against bacterial pathogens while only Bacillus strain showed the ef- fect against fungal pathogen. For endophytic traits, cellulase activity was ob- served in 5 classes, while pectinase activity was only in Proteobacteria. Fresh weight and vine length of sweet potato increased by inoculating mixed cul- tures of the isolates from each location.
be drawn between bacteria residing in the rhizosphere or phyllosphere (the aerial habitat influenced by plants) and bacteria living inside the plant, the so-called endo- phytes. Endophyticbacteria reside in specific tissues of the plant (such as root cortex or xylem) and develop a close association with the plant, with exchange of nutri- ents, enzymes (lipase, catalase, oxidase, etc.), functional agents (siderophores, biosurfactants, etc.), and also “sig- nals” [9, 10]. Endophytes colonize their plant host tissues in which they persist without exerting the negative effects of a pathogen (disruption of respiration, photosynthesis, translocation of nutrients, transpiration, etc.). On the contrary, the presence of these endophyticbacteria in the host plant leads to beneficial effects on its health and/or growth. Plantgrowth-promotingbacteria promote plant health and growth via three mechanisms: phytostimula- tion, biofertilization, and biocontrol .
The present investigation aimed to isolate and characterize endophyticbacteria from six selected medicinal plants (Ocimum sanctum, Aegle marmelos, Cinnamomum cassia, Azadirachta indica, Calotropis procera and Rauwolfia serpentina) with plantgrowthpromoting activities. Total 38 endophyticbacteria were isolated from the studied plant species by following standard microbiological culture methods. All the isolated bacteria were screened for the production of hydrolyzing enzyme and result of study revealed that maximum isolates have positive catalytic activity and this was followed by amylase, lipase and protease activities. While studying the antibacterial activity of the isolates, it was observed that fifteen isolates showed moderate to higher antibacterial activities against Escherichia coli, Pseudomonas aeruginosa & Staphylococcus aureus. Studies on plantgrowthpromoting activity suggested that 8, 12 & 6 isolates were positive for IAA production, siderophore production and phosphate solubilization activity respectively. Further, eight (21.05%) isolates were found positive for ammonia production. Through this investigation, endophyticbacteria isolated from medicinal plants with plantgrowthpromoting activities were reported, that can be further exploited for sustainable agriculture, with detail scientific investigation.
Pandey et al.  reported that endophytic Burkholderia sp. MSSP was found to exhibit PGP traits viz., ACC deaminase production, nitrogen fixation, phosphate solubilization, IAA production, siderophore production, HCN production and antagonistic activity against different phytopathogens; indicating its role in promotion of growth of host plant while colonizing the roots. Miliūtė and Buzaitė , isolated endophyticbacteria associated with apple tree buds. Nine isolates were shown to produce IAA. Amounts of IAA produced in culture varied between 0.12–0.24 micrograms per milligram of protein. Several bacterial endophytes were shown to produce siderophores and substances which inhibited the growth of the test strain. We also screened the isolates for other PGP traits, as abilities to solubilize phosphate and fix nitrogen. Janarthine and Eganathan  demostrated Sporosarcina aquimarina SjAM16103 was isolated from the inner tissues of pneumatophores of mangrove plant Avicennia marina could produce siderophore and IAA. Siderophores are iron chelating ligands which can be beneficial to plants by increasing the solubility of ferric iron (Fe III), which otherwise is unavailable for plant nutrition. The production of IAA enhances root growth of the plants by stimulating plant cell elongation or cell division. Witzel et al.  characterized the genome sequence of plantgrowthpromoting endophyte Enterobacter radicincitans sp. nov. DSM16656T, a new species of the genus Enterobacter which is a biological nitrogen-fixing endophytic bacterium with growth-promoting effects on a variety of crop and model plant species. They reported the presence of genes for nitrogen fixation, phosphorous mobilization, and phytohormone production reflects this microbe’s potential plantgrowthpromoting activity.
ABSTRACT: Plantgrowthpromotingendophytic rhizobacteria are usually involved with host plants in mutual interaction. They promote plantgrowth directly or indirectly, via production of phytohormones, biocontrol of host plant diseases or improvement of plant nutritional status. Here through this study, a bacterial strain was isolated from surface-sterilized root nodules of Mimosa pudica; which was screened through phenotypic, biochemical and physiological characterisation, in which the isolate was found to be Gram-negative, motile, capsulated, non-endospore forming rod with catalase production, acid production and starch hydrolysing ability. The isolate was also found to utilize carbon sources like mannitol, sucrose, glucose and galactose. Further the isolate was studied for determining its plantgrowthpromoting activity, by studying its biostimulating, biofertilising and biopesticidal activity. In each study the isolate showed a better result suggesting its significance in use as either a biostimulant, biofertiliser or a biopesticide as a sustinable agricultural approach.
Most commonly, phosphorus in soil is present in the form of insoluble phosphates and cannot be utilized by the plant species. The ability of bacteria to solubilize mineral phosphate has gained the development of agricultural microbiologists as it can induce the availability of phosphorus and iron for the plantgrowth. Plantgrowthpromotingbacteria have been shown to solubilize precipitated phosphorus and improve phosphate availability to plant the represent a possible mechanism of plantgrowth promotion under field conditions. Alive [free living] phosphate solubilizing bacteria release phosphate from additional soluble inorganic and organic phosphate compounds in soil and so contributes to increase available phosphate from the plants 18 .
growth promotion are the production of phytohormones, diazotrophic fixation of nitrogen, and solubilization of phosphate . In addition to that these bacteria also have ability to produce siderophore to chelate various metals, including Fe, Zn, and Cu [1,4] and also suppress pathogens by producing inhibitory compounds [24,42]. Bacterial endophytes have been reported to produce various phytohormones including Indole-3-acetic acid (IAA), cytokinin and gibberellins .Among these IAA is one of the most vital hormones, mainly due to its function in lateral and adventitious root formation  and root elongation  According to the , bacterial species belong to genera Pseudomonas, Pantoea, Bacillus, Klebisella, Enterobacter, and Serrartia have ability to produce IAA. Earlier studies have found that endophyticbacteria with the ability to produce IAA can enhance the growth of plants by increasing plant height and biomass [37, 38]. Most of the soil phosphorous is in the form of insoluble phosphate and cannot be utilized by the plant and phosphorous deficiency in plants result in an inhibited stem and root development, poor flowering, lack of seed formation . Endophyticbacteria can solubilize inorganic phosphate in soil by secreting organic acids and this in turn help to increase plantgrowth . Endophyticbacteria have a potential to use as an inoculant to promote plantgrowth due to these plantgrowth-promoting properties. Previous study indicated that Pantoea agglomerans YS19 can enhanced the biomass of the rice seedlings after application which can be attributed to their nitrogen-fixing ability and phytohormone production . A significant increase in the dry weight of leaf and root of rice plants has been recorded by rice plants inoculated with Bacillus subtilis .
Mangroves are highly productive ecosystems in tropical marine environment. Avicennia marina (Avicenniaceae), commonly known as grey or white mangrove occurs in the intertidal estuarine areas. It has aerial roots (pneumatophores); these grow to a height of about 20 centimetres, and a diameter of one centimetre. The only report stated that the genus Rivularia (heterocystous cyanobacterium) was commonly occurring on mangrove pneumatophores (Charles Lugomela and Birgitta Bergman 2002). But some nitrogen-fixing bacteria inhabiting barks of mangrove trees has been isolated and characterized (Uchino et al., 1984). However, there were no published reports on endophyticbacteria isolated from the pneumatophores of Avicennia marina. Therefore, the present study was aimed to isolate and to identify the endophyticbacteria from the pneumatophores of Avicennia marina, south east coast of India.
Microorganisms in the soil habitat play key roles in ecosystem functioning through controlling nutrient cycling reactions essential for maintaining soil fertility. They also contribute to the genesis and maintenance of soil structure (. Moreover these microorganisms affect the biogeochemical cycling of nutrients and consequently help plants to grow better both under conventional and stressed soil environment [41, 24]. Microbial communities inhabiting soils interact with plant roots and soil constituents at the root-soil interface , and hence, the rhizosphere is now considered as any volume of soil specifically influenced by plant roots and/or in association with root hairs and plant produced materials . Researchers are of the view that plantgrowthpromotingbacteria (PGPR) facilitate plantgrowth in either of the two ways. Firstly- PGPR may assist resource acquisition directly such as nitrogen, phosphorus and mineral etc. or they may modulate levels of hormones in plants as needed by them. Secondly- they promote plantgrowth indirectly also, and for it, they inhibit the effects of pathogens and thus act like biocontrol agents for the growth of plants .
In 1993, Ash et al. created the genus Paenibacillus based on phenotypic and phylogenetic considerations, such as 16S rRNA sequence analysis from the previous “group 3” of the genus Bacillus. The Latin root of this name is “Paeni” which means almost, so “Paenibacillus” means “almost Bacillus”. Paenibacillus belongs to the group of plantgrowth-promoting rhizobacteria (Timmusk et al., 2005). It is a free-living soil bacterium and has a relatively broad host plant range including wheat (Mavingui et al., 1992), barley (Ryu et al., 2005), garlic (Kajimura & Kaneda, 1996), and lodgepole pine (Holl & Chanway, 1992). In recent years, interest in Paenibacillus has increased considerably due to its application in agriculture and horticulture (e.g. P. polymyxa; Raza et al., 2008), industry (e.g. P. azoreducens; Meehan et al., 2001) and medicine (e.g. P. polymyxa strain SCE2; Seldin et al., 2002). A wide range of activities have been reported, including nitrogen fixation (Hong et al., 2009), phosphate solubilization (Hu et al., 2006), competition for nutrients and ecological niches (Timmusk et al., 2005), and the production of exopolysaccharides (Timmusk, 2003), lytic enzymes (Budi et al., 2000; Raza et al., 2008), antibiotics (Beatty & Jensen, 2002; Dijksterhuis et al., 1999; Li et al., 2007), and the plant hormones auxin (Lebuhn et al., 1997) and cytokinin (Timmusk et al., 1999). All these activities can contribute to plantgrowth promotion and also result in suppression of a wide range of plant pathogenic bacteria, fungi, and nematodes (Pichard and Thouvenot, 1999; Son et al., 2011). Paenibacillus does not spread systemically throughout plants, and accumulation sites are in intercellular spaces outside the vascular elements. They often form biofilms in the root tips (Timmusk et al., 2005). Biofilms are highly structured groups of cells with surface-adherent characteristics which are embedded in an extracellular matrix (Branda et al., 2005). Biofilm formation is suggested to be an important property of the bacteria which act as BCAs. The biofilms around plant roots prevent pathogen access to colonization sites and root exudates and thus nutrients (Weller & Thomashow, 2007).
Fungi, bacteria and viruses are biotic biocontrol agents that inhibits effects of the microbial pathogens in plant. The mode of action for bio control agents is antagonism, competition for nutrients and niches, prevention of colonization of host tissues by the pathogen and induction of resistance against the target diseases to be controlled.Cyanobacteria besides being a natural nitrogen fixer, they are paradigm of biocontrol agent combating multitude of plant pathogens via antagonism. They are equipped with potential to produce wide range of secondary metabolites  exhibiting antagonistic effects against different bacterial, viral and fungal plant pathogens . Multifarious secondary metabolites with effective inhibitory action are potent fungicides, herbicides and insecticides [34,35]. Different strains and extracts of cyanobacteria in various solvent effective against disease causing plant pathogens is presented in table 3.
PGPM can also act as biocontrol agents that protect the host plant from external harm. These bacteria can act as biological insecticides, nematicides, and fungicides, as well as, improving the plant's immune response to pathogenic bacteria and viruses (Glare et al., 2012). Biocontrol agents are generally less effective and slower acting than agrochemicals but are more selective in which pest species they kill. Suppressing the pest population and slower kill methods can still result in significant damage to the plant but can alter the pest population over time. Furthermore, they have a lower risk of widespread resistance (Parnell et al., 2016). Perhaps the most well-known example of a biocontrol insecticide is the bacteria, Bacillus thuringiensis (Bt). This spore forming bacteria produces a toxin during sporulation that, when ingested by dipterans, attacks the cells lining the gut (Carlton & González, 1986). Although this bacterium was
Wheat is considered the most wide spread culture in the world regarding the area harvested. In Romania, it is grown on approximately 25% of the arable land and 40% of the cereal grains. Improving wheat productivity and yield quality is a continuous concern. Therefore, plantgrowthpromoting microorganisms with biocontrol potential are of great interest for the farmers. In the present, five beneficial microorganisms, bacteria and fungi, were analysed as agro-inoculants. Their effect on wheat germination and growth initiation was evaluated in vitro. According to the biometric analysis best results were obtained when using Azospirillum brassilense and Bacillus amyloliquefaciens strains, although Trichoderma pseudokoningii and Bacillus endophyticus also improved wheat vigour indexes, compared to the untreated control. However, B. endophyticus 1T2 strain delayed the germination process. The dual culture assay performed against Fusarium graminearum, revealed that three strains B.amyloliquefaciens OS17, BW, and T.pseudokoningii Td85, have also biocontrol potential.
Pathogens affecting plant health are a major menace to food production and ecosystem stability worldwide . It has been estimated that approximately one third of the food crop is destroyed every year due to attack by insects, pathogenic fungi, bacteria, and nematodes . Botrytis cinerea is one of the most hazardous plant pathogen infecting a large number of vegetable plant. This phytopathogene infect leaves, stems, flowers and fruits of plants, either by direct penetration or through wounds caused by cultivation practices [3; 4; 5; 6].To control plant disease, producers had resort to the chemical products. However, many of the chemicals are hazardous and causes several negative effects on the environment and human health. For that reason, biocontrol has become an interesting alternative that are more "friendly" to the environment. Plantgrowthpromoting rhizobacteria (PGPR) are the important group of microorganisms, which play a major role in the biocontrol of plant pathogens . Bacillus species have been reported as plantpromotingbacteria in a wide
potential inoculant to the crop. We evaluated the genetic diversity of PGPB in the plant tissue of sugarcane varieties (RB 867515, RB 1011, and RB 92579). The primer BOX-A1R was used to differentiate the similar isolated and further sequencing 16S rRNA ribosomal gene. The 16S rRNA gene showed the presence of seven different genera distributed into four groups, the genus Bacillus, followed by Paenibacillus (20%), Burkholderia (14%), Herbaspirillum (6%), Pseudomonas (6%), Methylobacterium (6%), and Brevibacillus (3%). The molecular characterization of endophytic isolates from sugarcane revealed a diversity of bacteria colonizing this plant, with a possible biotechnological potential to be used as inoculant and biofertilizers.
Among such beneficial rhizospheric microflora, species of Pseudomonas and Bacillus are well known for their plantgrowthpromoting potential, aggressive rhizospheric colonization, and antagonistic abilities including the secretion of number of metabolites including antibiotics, volatile hydrogen cyanide (HCN), siderophores, lytic enzymes like chitinases and β 1, 3 glucanases. Pseudomonads have been reported for biological control of different fungal species such as Rhizoctonia, Fusarium, Sclerotium, Pythium and Macrophomina . Thus, the present work was designed to study the biocontrol efficacy of PGPR (Plantgrowthpromoting rhizobacteria) isolates against fungal pathogens that caused diseases in the seeds of Jatropha curcas.
glucose glycosidic linkages (Sullivan, 1997). The repetitive β-1, 4 glycosidic linkages results in long, straight chains of glucose molecules that can form extensive hydrogen bonds with adjacent, cellulose fibrils, which is known as crystalline cellulose. These structures are extremely stable and generate much of the strength of terrestrial plants. Chains of cellulose vary widely in length, dependent on the organism, and can reach upwards of 15 000 repeating glucose units with a molecular weight of 100 000g/mol (Sullivan, 1997). Cellulose is not limited to the plant kingdom and is also a component of various fungal and algal cell walls as well as its role as a common component of bacterial biofilms (Ross et al., 1991; Ude et al., 2006). For chemical cleavage of cellulose, a very high temperature and pressure is necessary to catalyze the crystalline cellulose transition into amorphous, water soluble cellulose.
PF15 showed the best inhibition of mycelium growth in the King B medium (the in vitro assay). This medium is deficient in iron that promotes pyoverdine synthesis by fluorescent Pseudomonas for chelating ferric ions, causing a reduction of its availability to the pathogen (Eyquem et al. 2000). These results suggest that the main mechanism of the PF15 strain is siderophore production in the medium poor in ferric ions (King B), but on the mixed medium and PDA, cumulative actions (antibiosis, parasitism) can be the origin of the antagonistic effect. However, the PP27 strain revealed a suppression of pathogen growth only on the King B medium, which explains that the main mechanism ex- pressed in vitro of this strain is siderophore production. Plants treated with fluorescent Pseudomonas (PF15, PP27 or their combination) showed the late on- set of symptoms, lesser rating scale and significant bioprotection against fusarium oxysporum f.sp. lycopersici (FOL). The specific resistance of plants is expressed as all or nothing (resistance/sensitiv- Figure 2. Disease incidence (A) and McKinney’s index (B) of Fusarium wilt in tomato plants grown in a split-root design Plants treated with PGPR strains Pseudomonas fluorescens PF15, Pseudomonas putida PP27 or their combination and challen- ged with fusarium oxysporum f.sp. lycopersici (FOL); data are means of 30 replicates for each treatment; protection of tomato plants is expressed as a reduction of the intensity of Fusarium wilt evolution relative to uninoculated plants, during 41 days of the disease following being under greenhouse conditions
To increase the productivity, are being carried out studies and research of bacteria capable of contributing to a better synthesis initial growth of seedlings pre- germinated. Endophyticbacteria have numerous functions for the plant, acting beneficial and showing satisfactory results and significant. Bacteria that inhabit the interior of the plant tissue can contribute effectively to the biological fixation of nitrogen, since the exchange is done directly, having this way a lesser competition for carbon sources, noting that not all micro-organisms are able to penetrate plant tissue.