Exopolysaccharides (EPS) of microbial origin is a promising alternative to chemical flocculants due to their sustainability and eco-friendly nature. In the present study, EPS produced by Bacillus cereus SK was studied and their flocculating activity was investigated. On incubation for 48 h, B. cereus SK produced 0.919 6 0.022 g/L of EPS from a cell mass of 3.59 6 0.06 g/L. The isolated EPS was identified as glycoprotein and chemical characterization by FTIR spectroscopic analysis suggested the presence of hydroxyl, amino and carboxyl groups. The kaolin clay flocculating activity of 83.4% was obtained on treatment with 12 mg/L of EPS. At 30% (v/v) of EPS 31.22 6 4.71 mL/g of Sludge volume index (SVI) and 34.44 6 1.51 mL/g of algal flocculation was observed. The EPS produced by B. cereus SK was non-toxic and did not exert any adverse effect on Danio rerio even at a concentration of 800 mg/mL.
The present work was focused on isolating a bacterial strain of Pseudomonas sp. with the ability to synthesise AgNPs rapidly. A strain of Pseudomonas aeruginosa designated JO was found to be a potential candidate for rapid synthesis of AgNPs with a synthesis time of 4h in light, at room temperature which is a shorter time period noticed for the synthesis when compared to the previous reports Biosynthesis of AgNPs was achieved by addition of culture supernatant with aqueous silver nitrate solution (1 mM). The reaction mixture exhibits change in colour from green to brown with a peak at 420 nm corresponding to the plasmon absorbance of AgNPs by UV-vis spectroscopy. The nanoparticles were characterised by X-ray diffraction (XRD), energy-dispersive X-ray analysis, Fourier-transform infrared spectroscopy, scanning electron microscopy (SEM), Zetasizer and transmission electron microscopy (TEM). The XRD spectrum exhibited 2θ values corresponding to the silver nanocrystals. TEM and SEM micrographs revealed the extracellular formation of polydispersed elongated nanoparticles with an average size of 27.5 nm. Synthesised nanoparticles showed antibacterial property against both gram-positive and gram-negative microorganisms, but more effective towards gram-negative.
Mangifera indica L. belongs to the family Anacardiaceae and is considered as “King of all Fruits”. Mango kernels are discarded as waste after the industrial processing and it has several proven medicinal benefits. Attempts were made to study its antitumour and antimicrobial activities. In the current research work, 15 local cultivars of Mangifera indica L. were collected with a motto to screen the best cultivar having high total phenolic content, flavonoid content, antitumour property and antimicrobial activity. Banganapalli cultivar of mango showed high total phenolic content and total flavonoid content i.e. 63.5±1.1 mg GAE/g and 16.7±0.5 mg quercetin/g followed by Royal special cultivar (TPC-58.7±0.6 mg GAE/g TFC-16.2±0.6 mg quercetin/g). Mangifera indica L. cultivar Banganapalli which showed highest total phenolic content and total flavonoid content was screened for its antitumour and antimicrobial properties. Antitumour property was tested by using potato disc assay which recorded 40.12% tumour inhibition percentage. Antimicrobial activity was assessed by agar diffusion method by taking 3 test microorganisms viz. Bacillus subtilis subsp. subtilis DSM 10, Staphylococcus aureus MTCC 737 and Escherichia coli MTCC 46. The measured area of inhibition is around Staphylococcus aureus MTCC 737 in 8.5±0.3 mm followed by E.coli MTCC 46 (8.2±0.3 mm) and Bacillus subtilis sub subtilis (6.6±0.5 mm). The present study showed that the mango kernels which were generally discarded as waste has antitumour and antibacterial properties and further studies need to be carried out.
Silica is a beneficial mineral that regulates the growth of plants and improves crop yields. Silica is a key factor in inducing the drought mitigation property and systemic acquired resistance in plants. Screening of silicate solubilizing bacteria on conventional medium forms white colonies on off-white media with translucent zones which makes the observation challenging. The present study used a modified plate assay by incorporating 0.0025% bromocresol purple in the Bunt and Rovira media which eases the screening process. The soil sample was collected from the maize rhizosphere, seven silicate solubilizing bacteria were isolated, among which SKSSB09 showed a better result. Bacillus tequilensis showed high silicate solubilization efficiency, that is, 546.23 ± 3.4 µg/mL with a silicate solubilization zone of 7.5 ± 0.6 mm. Gas chromatography-mass spectrometry analysis of the bacterial filter extracts detected the organic acids as propanoic acid, acetic acid, butanoic acid, and glycolic acid which are crucial factors in the dissolution of insoluble silicates. SKSSB09 also possess indole acetic acid production ability and the quantitative analysis showed 61.2 ± 3.6 µg/mL. SKSSB09 possess higher antagonistic activity which showed 99% of mycelial inhibition against Fusarium oxysporum. NCBI BLAST results of 16S rRNA gene sequence identified the SKSSB09 as B. tequilensis. This work highlights the importance of silicate solubilizing B. tequilensis SKSSB09 as a plant beneficial microbial inoculant.
Drought is an abiotic stress which causes huge economic losses in agriculture. Silicon is considered the best element which plays a key role in inducing drought mitigation properties. Silicate solubilizing bacterial strains were evaluated for their survivability in the low water activity potential. Bacillus tequilensis SKSSB09 showed high survivability at 40% polyethylene glycol 6000 concentration i.e. -1.76 MPa. ACC deaminase activity of the silicate solubilizing bacterial strains was assessed, among which B. tequilensis SKSSB09 showed ACC deaminase production in Dworkin and Foster minimal media. In–planta studies showed the survivability of maize plants till 23 days without water. Silicon deposition in the maize leaves showed 0.0384±0.0021μg/g. The leaf membrane stability index of the inoculated plants showed 72.2 ±3.8% which also correlates with the epicuticular wax content (2.4±0.56 mg/g). Proline content plays a key role in enhancing drought tolerance in plants. The inoculated plants showed high proline content (39.8±3.7 μg/g) which plays a key role in maintaining the cell sap and increasing the photosynthetic rate. Scanning electron microscopic studies revealed the deposition of silicon in the leaves and the formation of sunken stomata which reduces the transpiration rate. Based on the above results, Bacillus tequilensis SKSSB09 can be used as a plant growth-promoting rhizobacterial inoculant during drought conditions.
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