Modulation of agriculturally useful rhamnolipid profile of Pseudomonas sp. K6 due to the supplementation with chitosan and gold nanoparticles.

As rhizobacteria have extensively been studied for the production of compounds with biocontrol properties, methods to enhance its production are very important. In this study, nanotechnological method to modulate the rhamnolipid production by Pseudomonas sp. K6 has been demonstrated. For this, Pseudomonas sp. K6 was cultured with different concentrations of chitosan nanoparticles (CNPs) and gold nanoparticles (AuNPs). The rhamnolipid production was further analyzed by CTAB- methylene blue agar assay and also by LC-MS/MS analysis. From the LC-MS/MS result, induction of dirhamnolipid production in K6 could be confirmed when cultured with CNPs (1, 5 and 10 mg/mL) and AuNPs (10, 25, 50 and 100 µg/mL). The monorhamnolipid production by K6 was observed to get enhanced when the K6 culture was supplemented with 2.5 mg/mL CNPs and 10 µg/mL AuNPs. Also, in planta study confirmed the biocontrol ability of rhamnolipid as it suppressed the Sclerotium rolfsii infection in Vigna unguiculata plants. As the rhamnolipids have versatile applications in the agricultural field, the nano-based approach to enhance its production from the biocontrol organism is significant.

Kinetic study of gold nanoparticle mediated photocatalytic degradation of Victoria blue.

In the study, biogenic gold nanoparticles (AuNPs) were used for the photocatalytic degradation of triphenylmethane dyes Victoria blue B (VBB) and R (VBR). The process was found to result in an approximate degradation of 65 and 52%, respectively, for VBB and VBR within a period of 8 h. The relative rate of photocatalytic degradation of VBB and VBR was identified to be 0.0195 ± 0.0031/min and 0.0295 ± 0.0025/min, respectively, by using the Langmuir-Hinshelwood model. By using the Vigna unguiculata model system, the degradation products were demonstrated to have non-toxic effect. Moreover, the less toxic nature of AuNPs used for dye removal highlights its feasibility for large-scale application. Hence, the AuNPs-based photocatalytic dye degradation as described in the study is cost-effective, rapid and environment-friendly.

Pseudomonas fluorescens R68 assisted enhancement in growth and fertilizer utilization of Amaranthus tricolor (L.).

Plant probiotic potential of rhizosphere microbiome and its role in phytofertilizer mobilization are largely unexplored. In the current study, the rhizobacterium Pseudomonas fluorescens R68 (PFR68) isolated from Western Ghat was analyzed for its growth enhancement effect on the leafy vegetable Amaranthus tricolor (L.). One month of field growth of PFR68 inoculated A. tricolor has found to have enhanced growth parameters such as leaf number (1.57 fold), root number (1.76 fold), shoot length (1.28 fold) and fresh weight (2.31 fold). The treatment also improved soil fertility in terms of Nitrogen, Phosphorus and Potassium content. Most remarkably, application of PFR68 alone and 50% of recommended NPK dose along with PFR68 has resulted in enhanced growth of A. tricolor comparable to plants treated with full dose of NPK. In addition to this, application of PFR68 along with 50% NPK augmented the available Nitrogen and Phosphorus content in soil. This indicates the potential of selected organism in enrichment of soil health and enhancement of crop productivity. In conclusion, field performance of PFR68 on growth of A. tricolor confirms its promises to develop into plant probiotic formulation.

Strain-specific variation in plant growth promoting volatile organic compounds production by five different Pseudomonas spp. as confirmed by response of Vigna radiata seedlings.

AIM: Analysis of a blend of volatile organic compounds (VOCs) released by Pseudomonas spp. with growth-promoting effect in Vigna radiata seedlings. METHODS AND RESULTS: Plant growth-promoting activity of VOCs produced by five different Pseudomonas spp. was investigated by I-plate technique. VOCs produced by different organisms were extracted by various solvents (methanol, ethyl acetate, hexane and butanol) and were identified by gas chromatography-mass spectrometric analysis. The major VOCs identified were undecane, nonadecane, hexacosane, tetradecane, heptacosane, pentadecane, dodecane and tetratetracontane. The cultural conditions for the production of VOCs with plant growth enhancement effect were optimized and further confirmed using pure pentadecane as a candidate VOC. CONCLUSIONS: The study provides insight into plant beneficial effect of VOCs produced by Pseudomonas spp. Remarkable modulation in the production of VOCs with plant growth-promoting effect by rhizobacteria was found to be dependent on the bacterial strain and its concentration. SIGNIFICANCE AND IMPACT OF THE STUDY: The study describes the requirement to consider bacterial VOC production also for preparing plant probiotic formulations. As VOCs are least considered for preparation of commercial plant growth-promoting rhizobacterial strain formulation, the results of the study is highly significant.

Exploration of photocatalytic properties of microbially designed silver nanoparticles on Victoria blue B.

Victoria blue B (VBB) belongs to triphenylmethane group of dyes, which is widely used in textile industries. Hence development of novel treatment methods are of considerable applications in its removal. In the current study, silver nanoparticles (AgNPs) formed by Bacillus amyloliquefaciens was investigated for the degradation of VBB. Interestingly, the UV-Vis spectroscopy analysis of VBB-AgNPs treated samples showed a decrease in absorption at 615 nm, which is characteristic of pure VBB. This time-dependent degradation process was further investigated by changing the initial dye concentration, AgNPs concentration and pH. Approximately 78 % of reduction was observed within 8 h of the study and hence the result of the study is with promising applications for the development of novel dye degradation technologies. Phytotoxicity analysis of degradation product using Vigna unguiculata revealed the non-toxic effect of degradation product when compared to VBB and this confirms the promising potential and applications of the study.