Shalini Rajkumar

Mechanism of phosphate solubilization and antifungal activity of Streptomyces spp. isolated from wheat roots and rhizosphere and their application in improving plant growth.

The application of plant-growth-promoting rhizobacteria (PGPR) at field scale has been hindered by an inadequate understanding of the mechanisms that enhance plant growth, rhizosphere incompetence and the inability of bacterial strains to thrive in different soil types and environmental conditions. Actinobacteria with their sporulation, nutrient cycling, root colonization, bio-control and other plant-growth-promoting activities could be potential field bio-inoculants. We report the isolation of five rhizospheric and two root endophytic actinobacteria from Triticum aestivum (wheat) plants. The cultures exhibited plant-growth-promoting activities, namely phosphate solubilization (1916 mg l(-1)), phytase (0.68 U ml(-1)), chitinase (6.2 U ml(-1)), indole-3-acetic acid (136.5 mg l(-1)) and siderophore (47.4 mg l(-1)) production, as well as utilizing all the rhizospheric sugars under test. Malate (50-55 mmol l(-1)) was estimated in the culture supernatant of the highest phosphate solublizer, Streptomyces mhcr0816. The mechanism of malate overproduction was studied by gene expression and assays of key glyoxalate cycle enzymes - isocitrate dehydrogenase (IDH), isocitrate lyase (ICL) and malate synthase (MS). The significant increase in gene expression (ICL fourfold, MS sixfold) and enzyme activity (ICL fourfold, MS tenfold) of ICL and MS during stationary phase resulted in malate production as indicated by lowered pH (2.9) and HPLC analysis (retention time 13.1 min). Similarly, the secondary metabolites for chitinase-independent biocontrol activity of Streptomyces mhcr0817, as identified by GC-MS and (1)H-NMR spectra, were isoforms of pyrrole derivatives. The inoculation of actinobacterial isolate mhce0811 in T. aestivum (wheat) significantly improved plant growth, biomass (33%) and mineral (Fe, Mn, P) content in non-axenic conditions. Thus the actinobacterial isolates reported here were efficient PGPR possessing significant antifungal activity and may have potential field applications.

Layered inorganic nanocomposites: a promising carrier for 5-fluorouracil (5-FU).

We report here the intercalation of 5-fluorouracil (5-FU), an anticancer drug in interlayer gallery of Na(+) clay (Montmorillonite, MMT), with the assistance of biopolymer (chitosan, CS). The X-ray diffraction patterns, thermal and spectroscopic analyses indicated the drug intercalation into the clay interlayer space in support of CS and stabilized in the longitudinal monolayer by electrostatic interaction. In vitro drug release showed controlled release pattern. The genotoxic effect of drug was in vitro evaluated in human lymphocyte cell culture by comet assay, and results indicated significant reduction in DNA damage when drug was intercalated with clay and formulated in composites. The results of in vitro cell viability assay in cancer cells pointed at decreased toxicity of drug when encapsulated in Na(+)-clay plates than the pristine drug. In vivo pharmacokinetics, biodistribution, hepatotoxicity markers, e.g., SGPT and SGOT, and liver/testicular histology in rats showed plasma/tissue drug levels were within therapeutic window as compared to pristine drug. Therefore, drug-clay hybrid and composites can be of considerable value in chemotherapy of cancer with reduced side effects.

Biodegradable gelatin–ciprofloxacin–montmorillonite composite hydrogels for controlled drug release and wound dressing application

This work reports intercalation of a sparingly soluble antibiotic (ciprofloxacin) into layered nanostructure silicate, montmorillonite (MMT) and its reaction with bone derived polypeptide, gelatin that yields three-dimensional composite hydrogel. Drug intercalation results in changes in MMT layered space and drug loaded MMT and gelatin creates 3D morphology with biodegradable composite hydrogels. These changes can be correlated with electrostatic interactions between the drug, MMT and the gelatin polypeptides as confirmed by X-ray diffraction patterns, thermal, spectroscopic analyses, computational modeling and 3D morphology revealed by SEM and TEM analysis. No significant changes in structural and functional properties of drug was found after intercalation in MMT layers and composite hydrogels. In vitro drug release profiles showed controlled release up to 150h. The drug loaded composite hydrogels were tested on lung cancer cells (A549) by MTT assay. The results of in vitro cell migration and proliferation assay were promising as composite hydrogels induced wound healing progression. In vitro biodegradation was studied using proteolytic enzymes (lysozyme and protease K) at physiological conditions. This new approach of drug intercalation into the layered nanostructure silicate by ion-exchange may have significant applications in cost-effective wound dressing biomaterial with antimicrobial property.

Plant growth promoting potential and soil enzyme production of the most abundant Streptomyces spp. from wheat rhizosphere

To evaluate the plant growth promotion (PGP) potential and soil enzyme production under solid state fermentation (SSF) by most abundant Streptomyces spp. isolated from the wheat rhizosphere and to evaluate their effect on plant growth parameters.

Montmorillonite/poly-(ε-caprolactone) composites as versatile layered material: Reservoirs for anticancer drug and controlled release property

This work evaluates intercalation of tamoxifen (Tmx) in interlayer gallery of Na(+)-MMT (Montmorillonite, MMT) (Tmx-MMT), which is further compounded with poly-(ε-caprolactone) (PCL) (Tmx-MMT/PCL, MPs), for oral chemotherapy of breast cancer. The X-ray diffraction patterns, thermal and spectroscopic analyses indicated the intercalation of Tmx into the MMT interlayer that stabilized in the longitudinal monolayer mode by electrostatic interaction. No significant change in structural and functional properties of Tmx was found in the MMT layers. In vitro study of drug release profiles showed controlled release pattern. The genotoxic effect of drug was in vitro evaluated in human lymphocyte cell culture by comet assay, and results indicated moderate reduction in DNA damage when pristine Tmx was intercalated with MMT and formulated in composites. The Tmx-MMT hybrid efficacy was also confirmed on HeLa and A549 cancer cells by in vitro cell viability assay. In vivo pharmacokinetics (PK) of formulated Tmx in rats was examined and the results showed that plasma Tmx levels were within therapeutic window as compared to pristine Tmx. Therefore, Tmx-MMT hybrid and microcomposite particles (MPs) can be of considerable value in chemotherapy of malignant neoplastic disease with reduced side effects. This study clearly indicated that MMT not only plays a role as a delivery matrix for drug, but also facilitates significant increase in the delivery proficiency.

Exploring plant growth promoting potential of non rhizobial root nodules endophytes of Vigna radiata

Plant growth promoting (PGP) rhizobacteria exert beneficial effects and may establish as endophytes in their hosts. Here, plant growth promoting traits of 26 non rhizobial and one fungal endophyte previously isolated from Vigna radiata root-nodules were assessed for IAA and siderophore production, phosphate solubilization and hydrolytic enzymes production. Most bacterial endophytes improved seedling vigor index while fungal endophyte (Macrophomina phaseolina) lacked all PGP traits. Endophytes Ml, M10 and M15 were most influential in improving Seedling Vigor Index. Three endophytes having multiple PGP traits with maximum siderophore production: 46.77 μg mL−1 (Bacillus anthracis; Ml), IAA production: 10.81 μg mL−1 (Paenibacillus taichungensis; M10) and phosphate solubilization: 134.483 μg mL−1 (Paenibacillus xylanilyticus; M15) significantly increased root length (RL), shoot length (SL), number of lateral roots (NLR) and plant dry weight (DW) when inoculated/co inoculated with E. adhaerens (native rhizobia) to V. radiata in a small field trial. M10 inoculation produced longest RL while Ml when coinoculated with E. adhaerens produced highest SL and NLR. Ml inoculation or coinoculation was most effective in improving dry weight of mature plants. Most of the endophytes coinoculated with E. adhaerens improved growth parameters. We report that non rhizobial endophytes with PGP traits in combination with native rhizobia can be prospective candidates for use as biofertilizer.

Repression of oxalic acid-mediated mineral phosphate solubilization in rhizospheric isolates of Klebsiella pneumoniae by succinate

Two strains of Klebsiella (SM6 and SM11) were isolated from rhizospheric soil that solubilized mineral phosphate by secretion of oxalic acid from glucose. Activities of enzymes for periplasmic glucose oxidation (glucose dehydrogenase) and glyoxylate shunt (isocitrate lyase and glyoxylate oxidase) responsible for oxalic acid production were estimated. In presence of succinate, phosphate solubilization was completely inhibited, and the enzymes glucose dehydrogenase and glyoxylate oxidase were repressed. Significant activity of isocitrate lyase, the key enzyme for carbon flux through glyoxylate shunt and oxalic acid production during growth on glucose suggested that it could be inducible in nature, and its inhibition by succinate appeared to be similar to catabolite repression.

Nervous translation, do you get the message? A review of mRNPs, mRNA–protein interactions and translational control within cells of the nervous system

Abstract In neurons, translation of a message RNA can occur metres away from its transcriptional origin and in normal cells this is orchestrated with perfection. The life of an mRNA will see it pass through multiple steps of processing in the nucleus and the cytoplasm before it reaches its final destination. Processing of mRNA is determined by a myriad of RNA-binding proteins in multi-protein complexes called messenger ribonucleoproteins; however, incorrect processing and delivery of mRNA can cause several human neurological disorders. This review takes us through the life of mRNA from the nucleus to its point of translation in the cytoplasm. The review looks at the various cis and trans factors that act on the mRNA and discusses their roles in different cells of the nervous system and human disorders.

Evaluation of clay/poly (l-lactide) microcomposites as anticancer drug, 6-mercaptopurine reservoir through in vitro cytotoxicity, oxidative stress markers and in vivo pharmacokinetics

Intercalation of 6-mercaptopurine (6-MP), an antineoplastic drug in interlayer gallery of Na(+)-clay (MMT) was further entrapped in poly (L-lactide) matrix to form microcomposite spheres (MPs) in order to reduce the cell toxicity and enhance in vitro release and pharmacokinetic proficiency. The drug-clay hybrid was fabricated via intercalation by ion-exchange method to form MPs from hybrid. In vitro drug release showed controlled pattern, fitted to kinetic models suggested controlled exchange and partial diffusion through swollen matrix of clay inter layered gallery. The in vitro efficacy of formulated composites drug was tested in Human neuroblastoma cell line (IMR32) by various cell cytotoxic and oxidative stress marker indices. In vivo pharmacokinetics suggested that the intensity of formulated drug level in plasma was within remedial borders as compared to free drug. These clay based composites therefore have great potential of becoming a new dosage form of 6-MP.

Perspectives of PGPR in Agri-Ecosystems

Bacteria inhabiting the rhizosphere and beneficial to plants are termed as plant growth-promoting rhizobacteria (PGPR). A putative rhizobacteria qualifies as PGPR when it is able to produce a positive effect on the plant upon inoculation, hence demonstrating good competitive skills over existing rhizosphere communities. Generally 2–5% of rhizosphere bacteria are PGPR. A thorough understanding of the PGPR action mechanisms is fundamental to manipulating the rhizosphere in order to maximize the process within the system that influence plant productivity. Scientists have divided the mechanism of action into direct and indirect. Direct mechanisms are those that occur inside the plant and directly affect the plants metabolism while indirect mechanisms require participation of the plants defensive metabolic process, which transduce the signal sent from the bacteria influencing the plant. PGPR benefit plants indirectly by providing protection against phytopathogens by production of secondary metabolites, while direct mechanisms include production of phytohormones, nitrogen fixation, and phosphate solubilization. Hence, these plant-associated bacteria have implications as biofertilizers. A better understanding of the challenges in the development of PGPR as efficient commercial bioinoculants would facilitate the use of these organisms for sustainable agricultural development. This review article provides an insight into some of the very basic characteristics that define the persona of a PGPR strain and the developmental challenges faced by it.