Physiological and Biochemical Attributes of an Endophyte Stenotrophomonas maltophila, AVSW 1 Isolated from Chilli on   PGP of Tomato

Introduction

Tomato (Lycopersicon  esculentum  Mill)   is one of the rich source of vitamins, minerals, organic acids, essential amino acids and dietary fibres.Abiotic and Biotic factors(microbes) decreasing the production of tomato crop. Many Microbial diseases like Fusarium wilt ,Early blight , Late blight, damping off , Leaf spots, Bacterial fruit canker ,Anthracnose , bacterial  speck affecting  Tomato crop. Previous studies reports that ,soil nitrogen deficiency  is   decreasing quality and production of tomato crop, which  can be reclaimed by  potential  PGP  Bacteria  as an alternative  and eco friendly alternative to  chemical fertilizers  ^1-5.  Nowadays, bio inoculants have gained more global attention due to their eco-friendly, cost-effective and easily replicable nature and used in agricultural ecosystems because of the presence of plethora of secondary metabolites responsible for plant growth promotion ,stress tolerance and disease resistance ^6-11.Endophytic  bacteria  enhances plant growth by the production of IAA, Ammonia, Siderophore, secondary metabolites , solubilizing Phosphates  , increasing  pathogenicity  and  maintain  the  integrity of host cell wall^1,2,12,13.Due to  its close  association  with the host , they  developed  a  unique mechanism of synthesizing secondary metabolites for amicable association with the host in a symbiotic manner. Such specific secondary metabolites and volatile compounds express defence against fungi  and  bacteria ,induce systemic  resistance, immunity and enhance plant growth under  oxidative stress conditions^14-19.

Siderophores  produced  by plant growth promoting bacteria  are also involved in iron transportation and as biocontrol agents  by scavenging the available iron present in the surroundings of the pathogen siderophore production ²⁰.However, the metabolic profiling and physiological attributes of metabolites  from  endophytic bacteria  have not been much focussed. The present research   aimed to understand the metabolic profiling of an endophytic bacteria, Stenotrophomonas  maltophilia  isolate, extracted from green fruits of chilli and its physiological attributes in the growth promotion of tomato.

Isolation of Stenotrophomonas  maltophila  AVSW 1 

AVSW 1 an endophytic bacteria  isolated from the Green fruit of the chilli plant, was collected from Guntur, Andhra Pradesh, India .It was collected  from the corresponding author as a subject for the current research.AVSW 1 was purified by the streak plate method and grown in nutrient broth. After 48 hrs of incubation, the  endophytic  bacterial  strain was stored ^21-23.

Materials  and  Methodology

Screening of fungal antagonism and PGP activities 

The antifungal activity of AVSW 1 was assessed using the double culture method ²⁴.   Bacterial isolates were streaked on Sabouraud dextrose sugar (SDA) medium at 3 cm from the pathogenic fungi inoculated at the centre. Antifungal activity was measured at room temperature  after 4-7 days of incubation.  Inhibition levels were  measured  as I= 1-(a/b) X as described earlier ^{13-17, 25,26.}  

 Indole-3-acetic acid production

 One ml culture filtrate of 72 hrs old bacterial culture was supplemented with  1 μg. ml^{– l} L- tryptophan  and  2 ml Salkowski reagent  and incubated at 28 ± 20° C for 30 min. Appearance of  Pink colour  indicates the presence of IAA^27.

 Phosphate Solubilization

Solubilization of Tricalcium phosphate was detected in Pikovskaya’s agar ²¹. Bacterial isolate was streaked on the surface of the Pikovskaya agar medium, and activity was estimated after 1 to 5 days of incubation at room temperature. Development of the clear zone around the bacterial colony was a positive response for phosphate solubilization.

Ammonia Production

Fresh  bacterial culture was inoculated  into 10 ml of peptone water and incubated at 36 ± 2° C for 48-72 h.A change of colour from brown to yellow  with the addition of  0.5 ml of  Nessler’s  reagent was a positive reaction for ammonia production ²⁸_.

Siderophore Production

The bacterial strain was grown on a succinate medium and incubated for 24-30 h with constant shaking at 120 rpm at 28⁰ C.  For every 20 minutes of interval, 5 ml broth was taken and centrifuged at 10,000 rpm for 10 min at 4⁰ C. The cell-free supernatant was mixed with 0.5 ml CAS solution and colour was measured at 630 nm.0.5 ml un- inoculated succinate medium and 0.5 ml CAS solution was used as control ²⁸.

 Biochemical  Physiological and Molecular Identification

Biochemical tests such as The IMViC test, Indole test, MRVP, Citrate utilization, hydrogen sulphide production, and sugar fermentation were done as per the standard protocols ²⁹.

Physiological characteristics

 Amylase,Cellulase, Catalase, Oxidase,Urease, Gelatin hydrolysis, Nitrate reduction, Haemolysis and  Lecithinase  were analysed  as per the protocols ^29-32.

Molecular Identification 

It was done according to Bergey’s manual of determinative bacteriology ³³ for tentative identification of  Genus followed by  16S  rRNA  partial gene sequencing analysis using  universal  primer 1492R (5´-TACGGYTACCTTGTTACGACTT-3′) and 27F (5′ AGAGTTTGATCMTGGCTCAG-3′).Phylogenetic  tree analysis was done by using Neighbour joining method with 1000 bootstrap  replicates . Isolate was deposited in GenBank, NCBI ³⁴.

Optimization studies  

Physical parameters ,temperature, pH, incubation period, and chemical parameters  NaCl , carbon ,and nitrogen sources were studied in 10ml  of broth  inoculated with100 μl of bacterial culture and  incubated for 48 h .O.D of the culture broth was read at 600 nm ³⁵. Growth optimization of endophytic bacteria was analyzed at different temperatures ranging from 20-45°C at an interval of 5°C ,different pH value range [3-9] ,saline concentration range 1-6 % , 1% carbon sources ( Glucose, Fructose, Sucrose, Lactose, Maltose, Glycerol, Mannitol, Starch, and Cellulose) , 0,5%nitrogen sources (KNO3, NaNO3, NH4SO2, Urea, Peptone, Beef extract, Yeast extract, Casein, and Malt extract) and  incubation periods (24 h, 36 h, 48 h, 60 h and 72 h).Bacterial Growth Curve was also determined  for 24 h  bacterial culture at an interval of 4 h .

 PGP activity of endophyte by Pot Assay Studies: 

Tomato seeds were treated with 48 h bacterial culture for 30 min and shade-dried for 1 h. Inoculated seeds were seeded into coco peat,and the pots were kept under greenhouse conditions.% of seed germination was evaluated at an interval of 4,6 and 8 weeks. Physiological parameters , root length, shoot height ,biomass, no of leaves, no of lateral roots, and chemical constituents  Protein content by Lowry’s and  carbohydrate  content  by DNS method were estimated.

Metabolite profile Finger print of endophytic  bacteria

Secondary metabolite finger print of endophyte was analysed in ethyl acetate extract using   Fourier transforms infrared spectroscopy (FTIR) and GC-MS^36,37,39

Scanning Electron Microscopy

 Root colonization ability was studied using SEM. One cm of root pieces were fixed and then processed with the PATOTO method. The prepared samples were mounted on aluminium stubs with Scotch TM double-sided tape, coated with gold in a sputtering Hummer II (Technics,Springfield,VA) and examined in a Cambridge S360 Scanning Electron Microscope.

 Results and Discussion   

Fungal antagonism and PGP Traits 

Pure culture of AVSW 1 was screened for fungal antagonism against Fusarium oxysporum  by dual culture method as shown in Plate -1.AVSW 1 showed significant inhibition of  Fusarium  oxysporum  compared to control  and positive to PGP traits such as IAA, Ammonia, Phosphate solubilisation  and  siderophore  production  in  qualitative screening.

Plate 1: Screening of Fungal antagonism of AVSW 1 against Fusarium oxysporum. Click here to view Plate

 Effect of Physical and chemical parameters on Bacterial Growth:

Physicochemical parameters were analyzed on a one-time factor (OFOT) basis to optimize the growth and maximise the production of PGP traits. Optimization studies revealed that AVSW 1 showed maximum growth at 37 ⁰ C, 1% salinity and 60 h incubation period with minimal medium ameliorated with 1% Fructose and 1 %Peptone  (Fig 1).

The growth curve of S. maltophilia  AVSW 1 showed 4-8 h of Lag phase,12-44 h of Exponential phase, and 44-68 h of  stationary phase. After 68 h, the decline phase was observed (Fig2).

Figure 1: Optimization of Physical and Chemical parameters on  growth of AVSW 1. Click here to view Figure

Figure 2: Growth analysis of AVSW 1 from 4 – 96 h of incubation in optimized medium. Click here to view Figure

PGP traits of AVSW 1 

 Plant growth promotion (PGP) traits in  S. maltophilia AVSW 1, such as IAA, Ammonia, PO4- solubilization and siderophore production, were evaluated after optimization.(Table1 and fig2 ) In S. maltophilia AVSW 1,IAA production increased by 55.66 % ,Ammonia production increased by 74.85 % ,Phosphate (po4^– ) solubilization  increased by 69.42  % and Siderophore production increased by  49.62 % after Optimization. Whereas in earlier findings, S. maltophilia  JVB5, root endophyte of sunflower showed optimization were IAA (30.0 μg/ml) ,Phosphate solubilisation (32.23 ppm) and Siderophore (79.90 psu ) after optimization ⁴.Previous findings reported that two  S.maltophila  IPR-Pv696 and 262XG2 root nodular endophyte  strains of clover reported  IAA (30.26 μg /ml  and 31.15 μg/ml), Phosphate solubilization (100  and 75%) and phosphate liberated (278 mg/l and 208 mg/l )¹¹.10.73 μg /ml  phosphate solubilization, Indole acetic acid  3.16 μg/ml  and gibberellic Acid  40 μg /ml were observed in S. maltophilia , SBP-9 rhizobacteria of Sorghum bicolour  at pH 8, temperature 30 ⁰ C,Nacl Concentration 6 % and broth incubated for 48 h ⁶. 818 ppm  Phosphate solubilisation, 1,62 IU /ml Acid phosphatase , 93µg/ml  IAA production,  Ammonia production (80 µg/ml) and ability to produce  siderophore  and HCN  reported earlier in Stenotrophomonas maltophilia  AVP 27  rhizobacterium  of chilli ⁴⁰. Similarly ,  present  results also  revealed that S.maltophila  AVSW 1  is specific to the host in the expression of  PGP traits and varies with endophytic and  rhizospheric  habitats. Further observed that the ability of phosphate  solubilisation  is less in endophytic  strain  compared to  rhizosphere  strain. It may be a marker characteristic feature to distinguish  endophytic PGP strain from PGPR.

Table 1: Quantitative analysis of Plant growth promotion (PGP) traits in AVSW 1.

Optimization	IAA (μg/ml)	Ammonia (μg/ml)	PO4– solubilization (ppm)	Siderophore (psu)
Before (control)	14.17	15.07	33.6	33.33
After	25.1	33.1	69.33	55.33

Figure 3: Impact of optimization on Plant growth promotion (PGP) traits of AVSW 1  Click here to view Figure

Identification of AVSW 1     

Based on colony morphology, morphological, and physiological characteristics (Table 2) followed by 16s rRNA  partial gene sequencing analysis (Fig 4), AVSW 1 was identified as Stenotrophomonas maltophilia and deposited in  NCBI  GENBANK with the name Stenotrophomonas maltophilia AVSW 1 with the accession no OQ293900 

Table 2:  Colony morphology and Morphological, Biochemical and physiological Characteristics of  AVSW 1     

Morphological Characteristics
Colony Morphology	Small, circular and off white
Gram’s reaction	Positive
Cell shape	Rod
Biochemical Characteristics
Indole ,MR	Negative
VP/Citrate	positive
Sugar fermentations
Glucose /Sucrose/Fructose/Maltose/Mannitol	A+/G–
Lactose / Arabinose / Inositol / Sorbitol/Dulcitol	A–/G–
Physiological chaacteristics
Decarboxylation reactions
Ornithine/ Arginine / Creatinine/ Lysine	Positive
Malonate	Negative
Enzymatic reactions
Amylase/Urease /Super oxide dismutase/ Phenylalanine deaminase /Gelatin hydrolysis/ Oxidase	Negative
Cellulase peroxidases Poly phenyl oxidase Lecithinase Catalase Oxidase Nitrate reduction	positive
Haemolysis	Positive
Spore formation	Positive

Figure 4: Phylogenetic distance tree of Stenotrophomonas  maltophilia  AVSW  1 ( OQ293900) constructed by the neighbour-joining method using Blast N of NCBI  with 1000 bootstraps  Click here to view Figure

Greenhouse studies   

The plant growth promotion potential of  Stenotrophomonas  maltophilia AVSW 1  was tested on tomato seedlings using the seed bacterization method followed by inoculation of culture at the collar region under greenhouse conditions. Root colonization efficacy of AVSW 1 inoculum was observed on 4, 6 and 8week old seedlings treated with AVSW 1 under scanning electron microscope (Fig 5.A & 5.B).

Figure 5A: Scanning Electron Microgram of the root of tomato seedling treated with  AVSW 1. Click here to view Figure

Figure 5B: Scanning  Electron  Microgram showing clear root Colonization in AVSW 1 treated tomato seedlings        Click here to view Figure

Growth parameters such as root length,  shoot height, root shoot ratio, No of leaves and fresh weight, and nutritional metabolites (carbohydrates and proteins) were studied at intervals of two weeks from 4th week onwards using un inoculated   tomato seedlings as control.

Figure 6: Greenhouse studies of tomato seedlings treated with AVSW 1  Click here to view Figure

In previous findings, endophytic bacterial strains, namely CT12, CT 13 and CT 16 of S. maltophilia isolated from fruit, stem and leaf of tomatoes, respectively, showed nearly 35.9 % enhancement of shoot height and 19.6-28.3% root length of tomato seedlings  and also observed enhancement of fresh weight of shoot and root by 39.5 -57 % and 38.2 -58.8 % respectively under greenhouse conditions ⁴¹.

Similarly, Stenotrophomonas maltophilia BJ01  isolated from  halo tolerant grass species showed a 17.68 % enhancement of shoot height  and 57.14 % enhancement of fresh weight in peanut plants compared to control under high salt stress conditions  (100 mM  NaCl )⁹

In previous findings, Stenotrophomonas maltophilia  SBP-9  rhizospheric  isolate of Sorghum bicolour showed significant enhancement of 20 % shoot height , 28.81% root length , 28 % fresh weight and 42 % dry weight of the Plant and  18.40 % shoot fresh weight. It also reported that chlorophyll content increased by 55% at 150 mM  NaCl,  39 % at 200 mM NaCl  and 25 % at 200  mM NaCl when compared with 0 %  NaCl in wheat plants ⁶.

S.maltophilia  JVB5  isolated from sunflower root endosphere showed significant enhancement of root length ( 30.23 %), lateral roots (37.45 % ) and fresh weight (31.65%). IPR-Pv696 and 262XG2, two Bacillus toyonensis strains of root nodules of clover, showed a significant increase in fresh weight to (40.53 fed ^-1 and 42.68 tons fed ^-1), chlorophyll content by 4.51 % and carbohydrate content by 1.519 %, 20.18 % respectively ⁴ .

Similarly, in the present investigation, AVSW 1 treated tomato seedlings showed significant response in terms of the growth attributes and nutritive metabolites from the fourth week to the 8th (fig5.1 to 5.3). A significant increase of Shoot length (53.47 % ,41.85 % and 40.55 %) root length( 48.97 % , 48.76%  and 52.97 %), number of leaves (92.29 %, 69.07 %, 84.33 %), lateral roots (52.81 %,43.77 %, 37.08 % ), fresh weight of Plant (90.10 %, 99.60 %, 81.6 %) in 4 ^th, 6 ^th and 8 ^th weeks respectively in AVSW 1 treated plants compared to control (Fig 6 ). AVSW 1 treated plants also showed significant enhancement of protein and carbohydrate (66.66 %, 43.83 %, 45.75 % & 33.33 %, 33.96 %, 29.50 %) from 4^th week to 8^th week .Our results emphasized that the isolate AVSW 1 can promote plant growth and nutritional health and its antifungal activity against Fusarium oxysporum.

Based on the study, there is a significant increase in root and shoot length, number of leaves and lateral roots when compared with  control , protein and carbohydrate content and fresh weight  is more in inoculated seeds and seeds  treated with AVSW 1 inoculum showed better antifungal activity against  Fusarium  oxysporum .

Figure 7A: Root length and shoot height   on 4th ,6th and 8th week in treated and control plant Click here to view Figure

Figure 7B: Fresh weight and number of leaves on 4th, 6th and 8th week in  treated and control plants. Click here to view Figure

Figure 7C: Lateral roots, Protein and carbohydrate on 4th, 6th and 8th week in  treated and control Click here to view Figure

Figure 8: FTIR spectral analysis and interpretation of bioactive metabolites of Sphenotrophomonas maltophila  AVSW1. Click here to view Figure

Table 3: FTIR Spectral Data Analysis of Stenotrophomonas maltophila

Wavelength range	Functional groups and their bonds
3314.25	C-H stretch, Alkyne (strong, sharp)
3303.73	OH stretch normal polymeric
2944.98	C-H stretch, Alkane (medium)
2832.35	N-H stretch, Alcohol (weak, broad)
2042.92	N=C=N stretch, Isothiocyanate (strong)
1659.67	C=C stretch, Alkene (medium)
1449.21	C-H bend, Alkane (medium)
1414.57	S=O stretch, Sulfate (strong)
1114.16	C-O stretch, secondary alcohol (strong)
1019.84	C-F stretch, Fluoro compound (strong)

 In GC MS chromatogram   major peak was observed  at 6 min 8sec with the retention factor value of 43.00 with the molecular weight of 42.9582g/mol with the chemical formula C6H12O2.Compared to the NIST library, the primary compound was identified as 2-pentanone, 4-hydroxy, 4-methyl ester, which is confirmed by the FTIR results. Similarly, the compounds identified in the GC-MS analysis are confirmed to be the same as those in the FTIR analysis. As per the results of GC-MS, the profile of the AVSW 1 extract contains volatile organic compounds and secondary metabolites, which can efficiently control phytopathogens, increase plant growth, and induce systemic resistance^37-39.

Figure 9: GC-MS analysis  of metabolites of Stenotrophomonas  maltophila  AVSW1 at RT 6.30 GC-MS  Chromatogram of Stenotrophomonas  maltophila AVSW 1. Click here to view Figure

 Table 4: Metabolic Profile of  Bacterial extract of  AVSW 1  Stenotophomonas  maltophilia

S.No	RT	Height	Name of the compound	Molecular Formula	Mol wt	Area  % occupied	Norm %
1	6.830	30,461,028	2-Pentanone , 4-Hydroxy-4-Methyl-	C6H12O2	116	20.389	100
3	19.990	44,1313,68	Cyclopropane,1-(1-Methyethyl)-2-Nonyl-	C15H30	210	15.419	19.53
3	19.050	216,875,040	Glycine, N-Acetyl-N-(Trifluoro acetyl)-, Methyl Ester	C7H8F3NO4	227	13.917	18.88
4	17.559	106,691,120	2-Acetoxy  Iso butyryl Chloride	C6H9O3Cl	164	13.507	6.54
5	17.274	40,798,592	Propanoic Acid, 2-Oxo-, Methyl Ester	C4H6O3	102	12.275	60.20
6	18.500	52,147,852	Pentanoic Acid, 4-Oxo-	C5H8O3	116	7.883	66.24
7	7.395	20,769,012	2-Pentanone, 4-Hydroxy-4-Methyl-	C6H12O2	116	3.983	38.66
8	7.660	15,587,187	2-Hexanone, 6-Acetyloxy)	C8H14O3	158	3.849	16.79
9	18.640	35,413,672	5-Hydroxy pentane hydroxyl amine, N,O,OTriacetyl-	C11H19O5n	245	3.423	68.26
10	22.727	42,736,244	Ethanol, 2-(Octyloxy)-	C10H22O2	174	2.664	6.66
11	19.330	24,171,646	2-yclopenten-1-One, 2-Hydroxy -3,4-Dimethyl-	C7H10O2	126	1.357	75.62
12	16.194	13,718,134	2-Pentanone, 4-Hydroxy-4-Methyl-	C6H12O2	116	1.333	13.06

Figure 10: GC-MS spectrum of Active metabolites  of  Sphenotrophomonas maltophila AVSW 1 at RT  6.830   Click here to view Figure

Metabolic Profile of Bacterial Extract of AVSW 1  Stenotrophomonas maltophilia  

As per the NIST Database , bioactive metabolites such as 2-Pentanone, 4-Hydroxy-4-methyl, Cyclopropane,1-(1-Methyl ethyl)-2-Nonyl-, Glycine, N-Acetyl-N-(Trifluoro acetyl)-, Methyl Ester, 2-Acetoxy Iso butyryl  Chloride, Propanoic Acid, 2-Oxo-, Methyl Ester, Pentanoic Acid, 4-Oxo-,5-Hydroxypentanehydroxylamine, Ethanol, 2-(Octyloxy)-, 2-Cyclopenten-1-One, 2-Hydroxy-3,4-Dimethyl- , 2,2- Di methyl tetra hydro pyran-4-ol  showed bioactivities like root colonization, antifungal, high salinity stress tolerance, production of secondary metabolites and agrochemicals, signalling of molecules, enhanced microbial tolerance, anti-oxidation, cryoprotection, immune response, regulating  bacterial glycogen metabolism, gluconeogenesis,  anti-inflammatory,  plant defence mechanisms and promotes plant growth and metabolism.

In earlier studies ,  Stenotrophomonas maltophilia  UN1512  of strawberries reported the presence of Benzothiazole ,1,3,5,7-Cyclooctatetraene-1-carboxaldehyde, Carbonic Acid, octadecyl phenylester,  Benzaldehyde,2,5-bis[(trimethylsilyl)oxy]-,  Estragole  , and  Benzaldehyde , and  significantly inhibited the growth of  fungal pathogens  and promote growth of tomato plants  in vitro ⁴³. 

Volatile compounds like  haloalkanetrichloromethane,  2,4-dimethyl heptane and 4-methyl octane, furans and  dimethyl sulphide, α- and β-pinene, camphene, and Δ-3-carene were reported in  S.rhizophila  EP2.2  which are potential  antifungal metabolites against A.alternata  and  B.cinerea  ^{18 ,44-47,49,50}

Discussion

Currently, utilizing PGP bacteria in agriculture as Bio fertilizers and Bio inoculants is more winsome. Such bio inoculants protect plants from diseases and biotic and abiotic stress conditions by producing various regulatory chemicals, volatile organic compounds and secondary metabolites in the vicinity of the rhizosphere. Many Bacterial endophytes can colonize an ecological niche, making them potential  biocontrol agents against diseases.

Phosphate solubilising  endophytic  bioinoculant  is one of the alternative biotechnological solutions in sustainable agriculture to meet the phosphate demands of plants. IAA is one of the most crucial signal molecules in regulating plant growth. Salinity , pH and temperature  are primordial abiotic factors which control  plant growth, photosynthetic capacity, protein synthesis, energy, lipid metabolism, and total nitrogen content. PGP bacterial isolates which can have acclimatization to extreme high and low levels of salinity, pH and temperature  will be a potential  bioresource for sustainable  crop productivity. In present research the isolate ,  Stenotrophomonas maltophilia  AVSW 1 , showed  multiple potential by having acclimatization  to abiotic factors apart from direct (IAA, phosphate solubilisation, Ammonia) and  indirect  (HCN, volatile compounds , siderophore s)  mechanisms  . Secondary metabolites such as 2- Pentanone, 4-Hydroxy-4-methyl, Cyclopropane,1-(1-Methyl ethyl)-2-Nonyl-, Glycine, N-Acetyl-N-(Trifluoro  acetyl)-, Methyl Ester, 2-Acetoxy Iso butyryl Chloride, Propanoic Acid, 2-Oxo-, Methyl Ester, Pentanoic Acid, 4-Oxo-,5-Hydroxypentanehydroxylamine, Ethanol, 2-(Octyloxy)-, 2-Cyclopenten-1-One, 2-Hydroxy-3,4-Dimethyl- , 2,2- Di methyl tetrahydro pyran-4-ol  present in AVSW 1 are reported to be responsible for root colonization  and suppression of soil borne fungal pathogens . Hence tomato plants  inoculated with AVSW1 showed enhanced growth in greenhouse trials.  Further advanced technological intervention  can be useful  to bring potential formulation with this isolate Stenotrophomonas maltophila AVSW1.

Conclusion

In conclusion, Tomato plants inoculated with AVSW 1,an endophytic plant growth promoting bacteria isolated from chill roots effectively suppressed fungal (Fusarium oxysporum)  growth and exhibited significant growth-promoting traits and growth enhancement compared to untreated control. In this study, PGP isolate AVSW 1 showed maximum PGP traits in in-vitro conditions, perhaps can be used as a plant growth promoter in several vegetable or fruit crops. AVSW 1 improves plant growth directly through phosphate solubilization, production of secondary metabolites, volatile organic compounds, and growth hormones including nitrogen fixation. It reduces phytopathogens by sequestration of iron, secretion of siderophores, release of volatiles, etc. Further, the growth of plant pathogens may be directly inhibited by antibiosis. AVSW 1 may also induce systemic resistance in the host, where the plant defence mechanism gets activated against pathogen attack. The results indicate that Plant growth-promoting  rhizobacteria AVSW 1 isolated from  chilli roots can help the tomato plant withstand stress and support the Plant morphologically, physiologically, and biochemically. It can potentially promote tomato growth directly or indirectly, and further exploration of AVSW 1 as a bioinoculant can be tested at the field level to confirm its commercial significance. Genomic, proteomic and meta bolomics of holobiome (Plant and associated micro biome) and interdisciplinary research findings of AVSW 1 will be beneficial to understand its biocontrol  potential, mode of action, regulatory mechanisms, and plant-microbe interaction in detail.

Acknowledgement

The authors are thankful to the Acharya Nagarjuna Univeristy, Guntur, A.P  for providing the well-equipped Laboratories along with required infrastructure to complete the study.

Funding Sources

Authors are thankful to the DST-FIST Instrumentation centre(DST-Delhi SR/FST/LS-1/620/2015) of Dept of Botany and Microbiology of  Acharya Nagarjuna University, Guntur, Andhra Pradesh, India and the corresponding author thankful to University Grants commission for providing financial assistance of UGC-MRP (F.No 40-132/201(SR)).

Conflict of Interest

The authors declare that there is no conflict of interest

Data Availability Statement

The manuscript incorporates all datasets produced throughout the research study

Ethics Approval Statement

Not applicable  

Author’s contribution

Gadala Swapna   carried out the laboratory work, conceptualization, wrote the manuscript text and methodology. Amrutha   V. Audipudi was the supervisor of the research work

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