DSpace Collection:

Porous Particles for plant agronutrient delivery

Thu, 01 Apr 2021 00:00:00 GMT

Title: Porous Particles for plant agronutrient delivery Authors: Bindra, Pulkit; Vijayakumar, P. S. Abstract: Nutrients are the elements required by plants for the growth and reproduction, hence their deficiencies can severely affect the plant growth and yield. These nutrient requirements are met by supplementing the soil with fertilizers. However, these conventional fertilizers are susceptible to several issues like surface run off, leaching and environmental degradation etc. To overcome these problems, we have developed 3 approaches for a targeted, controlled and sustainable release. In the first study mesoporous silica particles were prepared as carriers and used for the application of a micronutrient viz., iron. The prepared carrier loaded with the nutrient was coated with a cationic biopolymer viz., chitosan to serve dual function in the developed targeted nutrient application system. 1. Chitosan acted as barrier to prevent the conversion of iron into its biologically unavailable forms by the carbonate and bicarbonates present in the soil, 2. acted as a interactive medium between mesoporous silica particles and plant roots to release the nutrient in targeted fashion. The coated particles showed a controlled and targeted release, and the findings were validated on tomato plant where the ferric chelate reductase activity (FCR). The FCR expression by the plant treated with the composite showed significantly reduction (by ~20%) compared to the uncoated and free form of fertilizer. In the second study we explored another type of porous particles in the form of metal organic frameworks (MOF) based on their chemical and physical properties like high surface area. The MOF were used as the carrier for the application of a macronutrient nitrogen in the form of urea. The ease of post synthesis modification in MOF allowed to coat biopolymer chitosan as used in our previous study. The coated particles showed a high loading capacity of 94% and sustained release pattern up to 48 hrs. The applicability of developed particle was validated in tomato plant, where the application of 6 mg of particle for 200 ml of hydroponic medium was able to meet the nitrogen requirement for the plants. In the third study we used low, dense cellulose with huge loading capacity as the fertilizer reservoir. However, the pore retention property of cellulose alone is quite poor for multiple cycles. To overcome this, a stable cellulose aerogel has been prepared by grafting porous silica on the surface. The aerogel prepared shows significantly more absorption capacity in the 5 th cycle than the fiber alone. Further this aerogel was used for urea loading and the release kinetics, which showed lower urea release kinetics than naked porous silica andcellulose, in acidic condition, which qualifies it to be a sustainable fertilizer reservoir in acidic soil.

Molecular insights into effector binding by gntr/fadr family sugar acid transcriptional regulators

Thu, 01 Jul 2021 00:00:00 GMT

Title: Molecular insights into effector binding by gntr/fadr family sugar acid transcriptional regulators Authors: Arya, Garima; Chaba, Rachna Abstract: Bacteria use a variety of carbohydrates as a source of carbon and energy. Sugar acids, the oxidized derivatives of sugars, represent an important class of carbohydrates whose metabolism is highly implicated in bacterial colonization and virulence. Sugar acids are widely prevalent in nature; they are an essential component of plant cell wall and animal tissues, and are produced as a metabolic intermediate of simple sugars by several microbes. In bacteria, the metabolism of sugar acids is often regulated by specific transcriptional regulators (TRs) that bind the operator DNA and activate or repress metabolic genes. The DNA binding ability of the sugar acid TRs is modulated by binding to cognate effectors, which are either the sugar acid itself or its metabolic intermediate. Several sugar acid TRs belong to the FadR subfamily within the GntR family of regulators. Although the DNA binding features and the effectors have been identified for a few FadR subfamily sugar acid TRs, the molecular details of effector-binding are completely unknown. Using Escherichia coli DgoR as a model, we presented the first comprehensive details into effector-binding among sugar acid TRs of GntR/FadR family. DgoR is a transcriptional repressor of D- galactonate metabolism and employs D-galactonate, the substrate of the metabolic pathway, as its specific effector. Through a combination of genetics, biochemical, and bioinformatics approaches, we identified the effector-binding cavity in DgoR. We employed a random mutagenesis-based genetic screen that exploited the accumulation of a toxic phosphorylated intermediate in the ΔdgoA strain, defective in D-galactonate metabolism, as a positive selection, to isolate several dgoR superrepressor alleles insensitive to D-galactonate. Blind molecular docking identified a potential effector-binding cavity in the C-terminal domain of DgoR and indicated that the amino acid residues corresponding to theeight dgoR superrepressor alleles constitute a part of the effector-binding pocket. The in- depth in vivo and in vitro analysis showed that the superrepressor alleles compromised the inducibility of DgoR without affecting its secondary structure, oligomeric status, and DNA binding ability. Further, taking Bacillus subtilis GntR, a repressor of D-gluconate metabolism, as a representative, we demonstrated that the effector binding pocket is similar among FadR subfamily sugar acid TRs. Finally, a comparison of sugar acid TRs with other FadR subfamily members suggested conserved features of effector-regulator recognition in FadR members that bind structurally similar effectors. Several studies have shown that genetic variations in carbohydrate sensing regulators affect their responsiveness to cognate effectors and ultimately influence the interaction of bacteria with their host. Thus, our study besides providing the basis for a detailed molecular understanding of sugar acid-responsive regulation in the FadR subfamily sets the ground to examine the influence of naturally occurring genetic variations in FadR subfamily regulators on their sensitivity to sugar acids and eventually their impact on bacterial colonization and virulence.

A study in host-pathogen coevolution and immune priming using laboratory populations of drosophila melanogaster

Wed, 01 Sep 2021 00:00:00 GMT

Title: A study in host-pathogen coevolution and immune priming using laboratory populations of drosophila melanogaster Authors: Ahlawat, Neetika; Prasad, N. G. Abstract: Organisms encounter various pathogens during their lifetime. Generating immune responses to combat these pathogenic attacks is critical to an organism’s fitness. This results in complex interactions between hosts and pathogens. In my thesis, I have addressed several important questions related to host-pathogen interactions. A major part of my work encompasses studying coevolutionary interactions between hosts and the pathogens. I compared a scenario of one-sided host evolution against a pathogen with a scenario where host and the pathogen coevolve. I used experimental evolutionary approach for this comparison and showed that these two scenarios can potentially be different. Further, I have also explored the occurrence of memory-like response i.e. immune priming in Drosophila melanogaster. I have specifically studied the trans-generational effects of parental immune priming in the F1 generation. I showed an individual role of mother and father in transferring memory-like response to their offspring.

Electrical Transport Characteristics of superconducting point-contacts

Fri, 01 Apr 2022 00:00:00 GMT

Title: Electrical Transport Characteristics of superconducting point-contacts Authors: Kumar, Ritesh; Sheet, Goutam Abstract: Mesoscopic junctions between normal metals and superconductors are often used as a tool for extracting energy, momentum, and spin-resolved spectroscopic information about the Fermi surface of metals and the amplitude and symmetry of the superconducting energy gap of super- conductors. The technique is commonly known as point contact spectroscopy (PCS). When the size of such a junction (a point contact) between two metals is comparable to the mean free path of the electrons, under the application of a voltage, the electrons either accelerate freely within the contact region (ballistic) or dissipate energy through inelastic scattering processes at the contact (thermal). In the ballistic regime, non-linearities in the current-voltage characteristics can be probed to spectroscopically investigate the interaction of the electrons with various exci- tations, like the phonons in a metal, magnons in a magnet and Bogolibuons in a superconductor. In the thermal regime, non-linearities may emerge from Joule heating of the point contacts. In an intermediate regime, where both ballistic and thermal features appear, the point contact spectra between normal metals and superconductors could mimic certain exotic spectral fea- tures that are theoretically predicted to emerge only for unconventional superconductors. Such “unconventional” features include multiple conductance dips and a large zero-bias conductance exceeding the limit of conventional Andreev reflection. Within a network resistor model, we have theoretically studied the role of non-ballistic transport characteristics for the emergence of such spectra when the superconductors are conventional in nature. We have also reproduced the theoretically calculated “unconventional” spectra in experiments using metallic point contacts between silver (Ag), a normal metal and niobium (Nb), a conventional superconductor. For the measurement of the transport characteristics of ballistic and non-ballistic super- conducting point contacts we have constructed a broadband point contact spectroscopy (PCS) probe that works down to 290 mK. This probe has a reliable transfer mechanism for tip and sample exchange at low temperatures. The sample holder is equipped with high-frequency connectors making it suitable for conventional low-frequency (<1 kHz) and high-frequency ( 200MHz) measurements. The PCS probe module is directly attached to the He-3 pot of a He-3 based refrigerator. The probe has been carefully designed to minimize the mechanical vibration at the tip and sample space. The sample and tip holders in the probe go inside a 7 Tesla superconducting magnet dipped in liquid helium for high-field experiments. We have used the home-built PCS probe to study the superconducting properties of Sr- intercalated Bi 2 Se 3 , a candidate topological superconductor. Bi 2 Se 3 is a topological insula- tor and upon Sr- intercalation, it superconducts below T c 2.9K at ambient pressure. Sr- intercalated Bi 2 Se 3 is especially interesting because it also displays a pressure induced re- entrant superconducting phase where the high-pressure phase shows almost two times higher T c than the ambient superconducting phase. Interestingly, unlike the ambient phase, the pressure- induced superconducting phase shows strong indication of unconventional superconductivity. However, since the pressure-induced phase remains inaccessible to the traditional spectroscopic itechniques, the detailed study of the phase remained an unattained goal. Based on our sub- kelvin PCS experiments, we have shown that the high-pressure superconducting phase of Sr- Bi 2 Se 3 can be realized under a mesoscopic point contact, where transport spectroscopy can be used to probe the nature of superconductivity. We discovered that the point contact junctions on the high-pressure phase show an unusual response to the magnetic field supporting the pos- sibility of unconventional superconductivity.