Bacillus licheniformis and Bacillus velezensis from Rhizosphere of Clerodendrum infortunatum L. Promote Plant Growth and Resistance to Sclerotium rolfsii in Vigna unguiculata (L.) Walp.

In the current study, thirty bacterial strains isolated from the rhizosphere of Clerodendrum infortunatum L. were evaluated for the properties related to the plant growth promotion and disease resistance. Here, all the selected strains were screened for its antagonistic effect towards the phytopathogen Sclerotium rolfsii and also for the production of bioactive compounds known to promote the plant growth. Among these isolates, CiRb1 and CiRb16 were observed to have a broad range of plant beneficial features and were identified as Bacillus licheniformis and Bacillus velezensis respectively. Both the isolates were also demonstrated to produce the volatile organic compounds (VOCs) responsible for the growth enhancement in Brassica nigra (L.) and growth inhibition of S. rolfsii. Talc based formulations made out of both B. licheniformis and B. velezensis were further demonstrated to augment the plant growth and protection against S. rolfsii in Vigna unguiculata (L.) Walp. By the GC-MS based analysis, undecane could also be detected in the methanolic extracts prepared from both B. licheniformis and B. velezensis. Here, the selected rhizobacterial isolates were found to promote the plant growth and disease resistance through both direct and VOC mediated mechanisms. The results of the study hence reveal both B. licheniformis and B. velezensis have the potential in field application to promote the growth and control of plant diseases.

Chitosan nanoparticles augmented indole-3-acetic acid production by rhizospheric Pseudomonas monteilii.

Rhizospheric Pseudomonas spp. are widely used for upgrading sustainable agriculture because of their ability to execute multifaceted plant beneficial functions. In the current study, chitosan nanoparticles (CNPs) were used to analyze their effect on plant beneficial properties of rhizospheric Pseudomonas monteilii. The CNPs were characterized by transmission electron microscopy (TEM) and dynamic light scattering (DLS) analysis. The impact of CNPs on indole-3-acetic acid (IAA) production of P. monteilii was analyzed and quantified by spectrophotometric and confirmed high-performance liquid chromatography analysis. This revealed the beneficial effect of CNPs (1 mg/ml) by enhancing the IAA production of P. monteilii. In planta effect of varied bacterial IAA production was further demonstrated in Vigna unguiculata. Here, enhancement in shoot length (35.79 ± 0.37 cm), leaf number (7 ± 0.54), and fresh weight (3.07 ± 0.11 g) were observed in the plants treated with the culture filtrate collected from P. monteilii cultivated with 1 mg/ml CNPs. The results of the study highlight the beneficial effect of the CNPs to augment the rhizobacterial functioning by inducing the expression of plant beneficial properties.

Chitosan and Gold Nanoparticles Supplementation for Augmentation of Indole-3-Acetic Acid Production by Rhizospheric Pseudomonas aeruginosa and Plant Growth Enhancement.

The present study has been focused to evaluate the effect of chitosan nanoparticles (CNPs) and gold nanoparticles (AuNPs) on the phytohormone production by rhizospheric Pseudomonas aeruginosa. The gold nanoparticles were synthesized biologically and characterized by UV-Visible spectrophotometry, transmission electron microscopy, and X-ray diffraction analysis. The indole-3-acetic acid (IAA) production by P. aeruginosa supplemented with CNPs and AuNPs was quantified by using Salkowski's method and confirmed by high-performance liquid chromatography (HPLC) analysis. This revealed the effect of 5 mg/mL CNPs and 100 µg/mL AuNPs to enhance the IAA production by P. aeruginosa. By Salkowski's method, 07.16 ± 0.28 and 09.56 ± 0.28 µg/mL of IAA could be detected in the samples prepared from P. aeruginosa supplemented with 5 mg/mL CNPs and 100 µg/mL AuNPs, respectively. HPLC analysis also confirmed the production of IAA by P. aeruginosa. The CNPs and AuNPs-supplemented P. aeruginosa was also found to have enhancement effect on the shoot length (25.25 ± 0.85 cm and 26.57 ± 0.73 cm) and fresh weight (0.94 ± 0.09 g and 0.96 ± 0.09 g) of Vigna unguiculata plants, which highlight the significance of the study and the agricultural promises of nanomaterials-supplemented rhizobacteria.

Biofilm and Biocontrol Modulation of Paenibacillus sp. CCB36 by Supplementation with Zinc Oxide Nanoparticles and Chitosan Nanoparticles.

Endophytic bacteria with multi-trait plant beneficial features have applications to enhance agricultural productivity by supporting the plant growth, yield, and disease resistance. In this study, Paenibacillus sp. CCB36 was isolated from the rhizome of Curcuma caesia Roxb., and its biofilm formation and antifungal properties have been evaluated in the presence of nanoparticles. Chitosan nanoparticles (CNPs) were synthesized and characterized by UV-visible spectrophotometry, Fourier transform infrared (FTIR) spectroscopy, high-resolution-transmission electron microscopic (HR-TEM) analysis, scanning electron microscopic (SEM) analysis, and dynamic light scattering (DLS). The effect of zinc oxide nanoparticles (ZnONPs) and CNPs on biofilm formation of Paenibacillus sp. CCB36 was evaluated by tissue culture plate assay. ZnONPs reduced its biofilm formation and was found to get modulated in the presence of CNPs as revealed by atomic force microscopy (AFM). Hence, CNPs were selected for further studies. Interestingly, biocontrol property of Paenibacillus sp. CCB36 against Rhizoctonia solani was also found to get enhanced when supplemented with chitosan nanoparticles. The results of the study indicate application of nanoparticles to improve colonization and active functioning of endophytic bacteria which can have significant application in agriculture.

Application of Encapsulated Bacillus licheniformis Supplemented with Chitosan Nanoparticles and Rice Starch for the Control of Sclerotium rolfsii in Capsicum annuum (L.) Seedlings.

Rhizosphere encourages the survival and functioning of diverse microbial communities through the influence of plant roots. Likewise, the rhizobacterial functioning contribute to the growth and productivity of crop plants significantly. With the advancement of nanotechnology, the nanoparticles can expect to augment the performance of plant beneficial microorganisms including the rhizobacteria and hence have the promise to boost sustainable agricultural practices. In the present study, Bacillus licheniformis encapsulated in alginate-chitosan nanoparticles (CNPs) beads supplemented with rice starch (RS) has been evaluated for its plant growth enhancement and disease control properties. The encapsulated Bacillus licheniformis was initially characterized for indole-3-acetic acid (IAA) production, nitrogen fixing capacity, 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase production and antifungal activity against Sclerotium rolfsii. In addition to this, the plant growth promoting and biocontrol properties of the encapsulated Bacillus licheniformis were also evaluated using Capsicum annuum (L.) (chilli) seedlings. From the results, the plants treated with encapsulated Bacillus licheniformis supplemented with CNPs were found to have maximum growth enhancement. At the same time, plants treated with encapsulated Bacillus licheniformis supplemented with CNPs and RS were found to have enhanced disease suppression. This revealed the application of encapsulated Bacillus licheniformis supplemented with CNPs and RS as a promising delivery system for agricultural applications.

Evaluation of plant probiotic performance of Pseudomonas sp. encapsulated in alginate supplemented with salicylic acid and zinc oxide nanoparticles.

Plant growth promoting rhizobacteria (PGPR) are efficient candidates for the application in agricultural field to enhance the crop yield and to suppress the plant diseases. As the changes in agro-climatic conditions negatively affect the soil fertility and functioning of soil microbial community, there are significant demand for the innovative delivery methods for the PGPR to ensure its optimal performance. In the present study, Pseudomonas sp. DN18 has been entrapped in the alginate beads along with the supplemented salicylic acid (SA) and zinc oxide nanoparticles (ZnONPs). This modified formulation was further demonstrated for the IAA production and also antifungal activity against the Sclerotium rolfsii. In addition, superior plant growth promoting and biocontrol properties of the encapsulated Pseudomonas sp. DN18 supplemented with SA and ZnONPs have also been demonstrated on Oryza sativa seedlings by comparing with the free living Pseudomonas sp. DN18. This revealed the agricultural promises of Pseudomonas sp. DN18 encapsulated in a modified delivery system due to its functional superiority and stability over the free living bacteria based formulation.

Rhizobacterial biofilm and plant growth promoting trait enhancement by organic acids and sugars.

In the study,Pseudomonas sp. K6 and Pseudomonas monteilii were found to form an enhanced biofilm when cultured in the presence of organic acids and sugars. Here, the highest biofilm could be observed for Pseudomonas sp. K6 (3.08 ± 0.13) and P. monteilii (1.99 ± 0.12) when cultured in presence of 10 µM malic acid. However, maximum production of indole 3 acetic acid (IAA) was observed with 25 µM succinic acid treatment for Pseudomonas sp. K6 (24.33 ± 0.57 µg ml-1) and with 25 µM galactose for P. monteilii (20 ± 0.0 µg ml-1). At the same time, Pseudomonas sp. K6 solubilized the highest quantity of phosphate in the presence of 50 µM citric acid (21.33 ± 0.0 µM) and P. monteilii was observed to produce 32.66 ± 1.25 µM soluble phosphate in the presence of 10 µM galactose. The results of the study demonstrate the role of organic acids and sugars in the enhancement of biofilm formation, IAA production and phosphate solubilization in selected Pseudomonas spp. and highlight the potential use of rhizobacteria in conjugation with supplement for the agricultural applications.

Biogenic Gold Nanoparticle Supplementation to Plant Beneficial Pseudomonas monteilii was Found to Enhance its Plant Probiotic Effect.

Rhizosphere provides unique space for intensive chemical conversation between plant and microorganisms. The common rhizobacterial mechanisms which have been demonstrated to promote plant growth include production of phytohormones, nitrogen fixation, synthesis of 1-aminocyclopropane-1-carboxylate deaminase (ACC deaminase) and phosphate solubilization. The microbially produced phytohormone indole-3-acetic acid (IAA) is considered to have significant role in interaction between plant and bacteria. Hence any substance with modulatory effect on rhizobacterial IAA production can expect to have its impact on plant-microbe interaction. With the advent of nanotechnology, nanoparticles are being used for diverse applications. However, applications of nanotechnology in agriculture have not been studied in detail. In the study, rhizospheric Pseudomonas monteilii was selected to investigate the concentration-dependent effect of biogenic gold nanoparticles (AuNPs) on its IAA production. For this, AuNPs synthesized by Bacillus subtilis SJ15 were characterized by UV-Vis spectroscopy, FT-IR, TEM and EDS. The results showed AuNPs to have spherical, hexagonal and triangular shapes with a size range of 12-32 nm and absorption peak at 545 nm. Further, various concentrations of AuNPs were used to identify its impact on IAA production by P. monteilii. From this, enhanced production of IAA by P. monteilii was found to take place in the presence of 50 µg/mL AuNPs. When Vigna unguiculata seedlings were grown in presence of 50 µg/mL of AuNPs, increased growth was observed. The results of the study thus showed the ability of AuNPs to augment the IAA-producing potential of P. monteilii.