Potassium solubilization by the selected strains was quantitatively measured using Aleksandrov broth. The bacterial isolates were introduced into a 40 ml volume of Aleksandrov broth and subjected to incubation in a rotary shaker operating at 4.26 g for a duration of 5 days at a temperature of 30°C. As a control, broth was autoclaved. After incubation, pH of the broth was noted. Post incubation, the broth was centrifuged at a speed of 42,600 × g for 10 min. The supernatant was collected and then utilized for the purpose of measuring the concentration of soluble potassium using a flame photometer. Various concentrations (20, 30, and 40 mg L−1) of potassium chloride solution were prepared as standard solutions for the measurement of present K levels (Rajawat et al., 2016 (link)).
The potential of Zn solubilization by the isolated bacteria was quantitatively checked by following the protocol proposed by Fasim et al. (2002 (link)). Overnight grown bacterial cultures (2.5% inoculum) were inoculated in tris minimal salts medium (250 ml) supplied with 14 mM zinc oxide and non-supplemented medium was used as a control without inoculation. Bacterial strains were kept on orbital shaker to incubate for 10 days at 30°C. The pH of samples was measured every day. The medium was centrifuged and the supernatants were collected. The supernatants were acidified using 6 M HNO3 and the soluble ZN content was measured by atomic absorption spectrophotometry (AAS). The solubilized zinc content was determined by measuring the difference between the soluble zinc in the inoculation sample and the equivalent control and expressing it as grams of Zn ml−1 culture.
National botanical research institute's phosphate (NBRIP) medium was utilized to quantitatively measure the phosphate solubilizing ability of isolated bacteria (Nautiyal, 1999 (link)). The cultures were grown for 24 h and then 1 ml culture was inoculated into 50 ml NBRIP medium. The medium was put in an incubator at 17.04 × g for 6 days at 28±2°C in an orbital shaking incubator. The pH of the medium was recorded and uninoculated medium taken as a control. Post incubation, the cultures were subjected to centrifuge at 27,264 × g for 20 min and supernatants were obtained. Available phosphate in the culture supernatants were quantified by following the vanadomolybdophosphoric acid colorimetric method (Kumar et al., 2009 (link)).
The potential of Zn solubilization by the isolated bacteria was quantitatively checked by following the protocol proposed by Fasim et al. (2002 (link)). Overnight grown bacterial cultures (2.5% inoculum) were inoculated in tris minimal salts medium (250 ml) supplied with 14 mM zinc oxide and non-supplemented medium was used as a control without inoculation. Bacterial strains were kept on orbital shaker to incubate for 10 days at 30°C. The pH of samples was measured every day. The medium was centrifuged and the supernatants were collected. The supernatants were acidified using 6 M HNO3 and the soluble ZN content was measured by atomic absorption spectrophotometry (AAS). The solubilized zinc content was determined by measuring the difference between the soluble zinc in the inoculation sample and the equivalent control and expressing it as grams of Zn ml−1 culture.
National botanical research institute's phosphate (NBRIP) medium was utilized to quantitatively measure the phosphate solubilizing ability of isolated bacteria (Nautiyal, 1999 (link)). The cultures were grown for 24 h and then 1 ml culture was inoculated into 50 ml NBRIP medium. The medium was put in an incubator at 17.04 × g for 6 days at 28±2°C in an orbital shaking incubator. The pH of the medium was recorded and uninoculated medium taken as a control. Post incubation, the cultures were subjected to centrifuge at 27,264 × g for 20 min and supernatants were obtained. Available phosphate in the culture supernatants were quantified by following the vanadomolybdophosphoric acid colorimetric method (Kumar et al., 2009 (link)).
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