Broad-spectrum pH functional chitosan-phosphatase beads for the generation of plant-available phosphorus: utilizing the insoluble P pool.

Utilization of organic phosphates and insoluble phosphates for the gradual generation of plant-available phosphorus (P) is the only sustainable solution for P fertilization. Enzymatic conversions are one of the best sustainable routes for releasing P to soil. Phosphatase enzyme aids in solubilizing organic and insoluble phosphates to plant-available P. We herein report the preparation of highly functional chitosan beads co-immobilized with acid phosphatase and alkaline phosphatase enzymes via a glutaraldehyde linkage. The dual enzyme co-immobilized chitosan beads were characterized using Fourier-transform infrared (FTIR), thermogravimetric (TGA), and scanning electron microscopy-energy dispersive x-ray (SEM-EDX) analyses to confirm the immobilization. The co-immobilized system was found to be active for a broader pH range of ∼4-10 than the individually bound enzymes and mixed soluble enzymes. The bound matrix exhibited pH optima at 6 and 9, respectively, for acid and alkaline phosphatase and a temperature optimum at 50°C. The phosphate-solubilizing abilities of the chitosan-enzyme derivatives were examined using insoluble tri-calcium phosphate (TCP) for wide pH conditions of 5.5, 7, and 8.5 up to 25 days. The liberation of phosphate was highest (27.20 mg/mL) at pH 5.5 after the defined period. The residual soil phosphatase activity was also monitored after 7 days of incubation with CBE for three different soils of pH ∼5.5, 7, and 8.5. The residual phosphatase activity increased for all the soils after applying the CBE. The germination index of the Oryza sativa (rice) plant was studied using different pH buffer media upon the application of the CBE in the presence of tri-calcium phosphate as a phosphate source. Overall, the dual-enzyme co-immobilized chitosan beads were highly effective over a wide pH range for generating plant-available phosphates from insoluble phosphates. The chitosan-enzyme derivative holds the potential to be used for sustainable phosphorus fertilization with different insoluble and organic phosphorus sources.

Intercalation vs Adsorption Strategies of Myo-Inositol Hexakisphosphate into Zn-Fe Layered Double Hydroxide: A Tiff between Anion Exchange and Coprecipitation.

Myo-inositol hexakisphosphates (IHPs) or phytates are the most abundant organic phosphates having the potential to serve as a phosphorus reserve in soil. Understanding the fate of IHP interaction with soil minerals tends to be crucial for its efficient storage and utilization as a slow-release organic phosphate fertilizer. We have systematically compared the effective intercalation strategy of a phytate onto Zn-Fe layered double hydroxide (LDH) acting as storage/carrier material through coprecipitation and anion exchange. Powder X-ray diffraction, X-ray photoelectron spectroscopy, elemental analysis, thermogravimetric analysis, FTIR spectra, and molecular modeling demonstrated the formation of phytate-intercalated Zn-Fe LDH through coprecipitation with a maximum loading of 41.34% (w/w) in the pH range of ∼9-10 in a vertical alignment through monolayer formation. No intercalation product was obtained from the anion exchange method, which was concluded based on the absence of shifting in the XRD (003) peak. A change in the zeta potential values from positive to negative and subsequent increase in solution pH, with decreasing phytate concentration, are suggestive of adsorption of IHP onto the LDH surface. The batch adsorption data were best fitted with Langmuir isotherm equation and followed the pseudo-second-order kinetic model. The maximum adsorption capacity was found to be 45.87 mg g-1 at a temperature of 25 ± 0.5 °C and pH 5.63.

Boosting nitrogen fertilization by a slow releasing nitrate-intercalated biocompatible layered double hydroxide-hydrogel composite loaded with Azospirillum brasilense.

Indiscriminate use of chemical fertilizers leads to soil environmental disbalance and therefore, preparation and application of environment-friendly slow-release multifunctional fertilizers are of paramount importance for sustainable crop production in the present scenario. In this study, we propose a slow-release multifunctional composite nitrogen (N) fertilizer, which possesses the ability to supply plant accessible N in the form of ammonium (NH4 +) and nitrate (NO3 -) to improve nitrate assimilation coupled with zinc (Zn, a major micronutrient for plants in the soil) after its degradation. For this purpose, NO3 --intercalated zinc-aluminum (Zn-Al) layered double hydroxide (LDH) was synthesized using a co-precipitation protocol. The prepared LDH was added as 25.45% of total polymer weight to a sodium carboxymethyl cellulose/hydroxyethyl cellulose citric acid (NaCMC/HEC-CA) biodegradable hydrogel. A. brasilense, commonly used nitrogen-fixing bacteria in soils, was added to the LDH-hydrogel composite along with LDH alone to augment the availability of NH4 + and NO3 -. Adjusting the pH under acidic (pH 5.25) and neutral (pH 7) conditions, the release pattern of NO3 - from LDH and the composite was monitored for 30 days at normal temperature. The pH was selected based on the soil analysis data of North East India. The LDH-composite released 90% (w/w) and 85.45% (w/w) of intercalated NO3 - at pH 5.25 and 7.00 respectively in 30 days. However, 100% (w/w) and 87% (w/w) of intercalated NO3 - at pH 5.25 and 7.00 respectively were released in 30 days when only LDH was applied, which indicated the lower performance of LDH alone in comparison to the LDH-composite for the nitrate holding pattern. The pH of the bacteria-loaded system was observed to be acidic (pH = 5-6) during the study of nitrate assimilation and Zn2+ release. A. brasilense improved nitrate assimilation and increased the NH4 + ion concentration in the studied system. A significant increase in Zn2+ release was observed from day 5 in the presence of A. brasilense in the LDH-composite compared with that in the absence of A. brasilense. In conclusion, the prepared LDH-hydrogel-A. brasilense composite fertilizer system increases the availability of plant accessible N form (both NO3 - and NH4 +) and can potentially improve soil fertility with the addition of Zn and bacteria to the soil in the extended course.

Silent Hypoxia in Coronavirus disease-2019: Is it more dangerous? -A retrospective cohort study.

Background: Hypoxia in patients with COVID-19 is one of the strongest predictors of mortality. Silent hypoxia is characterised by the presence of hypoxia without dyspnoea. Silent hypoxia has been shown to affect the outcome in previous studies. Methods: This was a retrospective study of a cohort of patients with SARS-CoV-2 infection who were hypoxic at presentation. Clinical, laboratory and treatment parameters in patients with silent hypoxia and dyspnoeic hypoxia were compared. Multivariate logistic regression models were fitted to identify the factors predicting mortality. Results: Among 2080 patients with COVID-19 admitted to our hospital, 811 patients were hypoxic with SpO2 <94% at the time of presentation. Among them, 174 (21.45%) did not have dyspnoea since the onset of COVID-19 symptoms. Further, 5.2% of patients were completely asymptomatic for COVID-19 and were found to be hypoxic only on pulse oximetry. The case fatality rate in patients with silent hypoxia was 45.4% as compared to 40.03% in dyspnoeic hypoxic patients (P = 0.202). The odds ratio of death was 1.1 (95% CI: 0.41-2.97) in the patients with silent hypoxia after adjusting for baseline characteristics, laboratory parameters, treatment and in-hospital complications, which did not reach statistical significance (P = 0.851). Conclusion: Silent hypoxia may be the only presenting feature of COVID-19. As the case fatality rate is comparable between silent and dyspnoeic hypoxia, it should be recognised early and treated as aggressively. Because home isolation is recommended in patients with COVID-19, it is essential to use pulse oximetry in the home setting to identify these patients.