From Regulation of Secondary Metabolites to Increased Virulence under Sublethal Dosage of Antibiotics: An Unprecedented Role of Global Regulator, MftR, in Burkholderia thailandensis

The rise of multi-drug resistant bacteria combined with a decreasing pool of effective antibiotics has placed an increasing need for the development of novel antibiotics. Bacterial natural products or secondary metabolites have been the greatest source for development of novel antibiotics. The genus Burkholderia has recently emerged as a source of promising compounds with antibacterial, antifungal, and anti-cancer activities. Bacterial secondary metabolites provide added advantage to bacteria under stressful environments such as during host infection, evading predators or nutrient deficient conditions. However, genes involved in synthesis of these novel compounds remain silent under normal laboratory growth, creating a hurdle in isolation and characterization of these compounds. Understanding the underlying mechanism of how these genes are regulated could hold the key to unlocking the production of the secondary metabolites. A large number of biosynthetic gene clusters in Burkholderia thailandensis are known to be under direct or indirect control of the global regulator, MftR (Major facilitator transport regulator). MftR, a MarR (Multiple antibiotics resistance regulator) homolog, is conserved even in the pathogenic strains. My work focuses specifically on the role of MftR in regulation of genes encoding proteins required for production two secondary metabolites involved in increasing fitness of the bacteria through increased virulence a) malleilactone, a cytotoxic compound, and b) malleobactin, the major siderophore. The data presented here indicate that under normal growth conditions MftR directly represses the expression of genes encoding local activators, MalR and ECF (extra-cytoplasmic sigma factor), which are essential for production of malleilactone and malleobactin, respectively. Further, my work shows disruption of the purine metabolic pathway induced by sub-lethal dosage of trimethoprim in B. thailandensis, and that such disruption leads to increased virulence as indicated by increased killing of Caenorhabditis elegans by bacterial cells grown with trimethoprim. Moreover, disruption of mftR makes B. thailandensis more virulent as indicated by increased motility, biofilm production, siderophore production, killing of C. elegans, and rot on onion bulb. Overall, the work conducted so far not only addresses the role of secondary metabolites, malleilactone and malleobactin, in virulence of bacterial physiology, but also that targeting a global regulator could be an effective way of eliciting production of secondary metabolites. Moreover, the role of a global regulator in increasing bacterial fitness under antibiotic stress through production of secondary metabolites is highlighted

Physico-chemical and structural characterization of mucilage isolated from seeds of Diospyros melonoxylon Roxb.

Mucilagem foi isolada de sementes de Diospyros melanoxylon Roxb, uma planta que cresce naturalmente nas florestas da Índia. Vários métodos físico-químicos, como análise de partículas, microscopia electrônica, calorimetria diferencial de varredura, análise térmica diferencial, análise termogravimétrica, massa molecular por cromatografia de permeação em gel, viscosidade, análise elementar, espectrometria de difração de raios-x, potencial zeta, espectroscopia no infravermelho com transformada de Fourier, 1D (1H e 13C) (NMR) foram utilizados no presente estudo para caracterizar essa goma. A análise de partículas sugere que a mucilagem tem tamanho de partícula em nm. A análise SEM sugere que a mucilagem tem tamanho de partícula irregular. Observou-se temperatura de transição vítrea da goma de 78 °C e 74 °C por DSC e DTA, respectivamente. A análise termogravimétrica sugeriu que a mucilagem possuía boa estabilidade térmica, com duas fases de decomposição. A massa molecular da mucilagem foi 8760, por meio de cromatografia de permeação em gel, enquanto que a viscosidade foi 219,1 cP. O padrão de DRX da mucilagem indicou natureza completamente amorfa. Os principais grupos funcionais identificados a partir do espectro de FT-IR foram: 3441 cm-1 (-OH), 1632 cm-1 (-COO-), 1414 cm-1 (-COO-) e 1.219 cm-1 (CH3CO-). As análises de mucilagem por cromatografia em papel e 1D RMN indicaram a presença de açúcares.Mucilage was isolated from the seeds of Diospyros melonoxylon Roxb., a plant growing naturally in the forests of India. Various physico-chemical methods like particle analysis, scanning electron microscopy, differential scanning calorimetry, differential thermal analysis, thermogravimetry analysis, molecular weight by gel permeation chromatography, rheometry, elemental analysis, x-ray diffraction spectrometry, zeta potential, fourier transform infrared spectroscopy, 1D(1H and 13C) (NMR) have been employed to characterize this gum in the present study. Particle analyses suggest that mucilage had particle size in nanometer. SEM analysis suggested that the mucilage had irregular particle size. The glass transition temperature of the gum observed was 78 °C and 74 °C by DSC and DTA respectively. The Thermogravimetry analysis suggested that mucilage had good thermal stability with two stage decomposition. The molecular weight of mucilage was determined to be 8760, by gel permeation chromatography, while the viscosity of mucilage was observed to be 219.1 cP. The XRD pattern of the mucilage indicated a complete amorphous nature. Elemental analysis of the gum revealed specific contents of carbon, hydrogen, nitrogen and sulfur. The major functional groups identified from FT-IR spectrum include 3441 cm-1 (-OH), 1632 cm-1 (-COO-), 1414 cm-1 (-COO-) and 1219 cm-1 (-CH3CO). Analysis of mucilage by paper chromatography and 1D NMR indicated the presence of sugars

In vivo mucoadhesive strength appraisal of gum Manilkara zapota

Mucilagem (MMZ) extraída das sementes de Manilkara zapota(Linn.) P. Royen syn utilizando técnicas de maceração foi avaliada por sua força mucoadesiva por vários métodos in vitro e in vivo. O resultado mostrou que a força mucoadesiva das sementes mucilaginosas tem propriedade comparável aos polímeros naturais e sintéticos, tais como goma Guar e hidroxipropilmetil celulose (HPMC E5LV) nas condições experimentais utilizadas neste estudo. Brevemente, se pode concluir que a mucilagem de semente de Manilkara zapota pode ser usada como um excipiente farmacêutico em sistemas de liberação de fármacos mucoadesivos por via oral. Pode ser apropriado o estudo posterior de mudanças nessas propriedades após modificações químicas.The mucilage (MMZ) extracted from the seeds of Manilkara zapota(Linn.) P. Royen syn. using maceration techniques was evaluated for mucoadhesive strength by various in vitro and in vivo methods. The result showed that mucoadhesive strength of seeds mucilage have comparable property toward natural and synthetic polymers such as Guar Gum and hydroxyl propyl methyl cellulose (HPMC E5LV) under the experimental conditions used in this study. Briefly, it could be concluded that the seed mucilage of Manilkara zapota can be used as a pharmaceutical excipient in oral mucoadhesive drug delivery systems. Further, it may be appropriate to study the changes in these properties after chemical modifications

Do global regulators hold the key to production of bacterial secondary metabolites?

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. The emergence of multiple antibiotic resistant bacteria has pushed the available pool of antibiotics to the brink. Bacterial secondary metabolites have long been a valuable resource in the development of antibiotics, and the genus Burkholderia has recently emerged as a source of novel compounds with antibacterial, antifungal, and anti-cancer activities. Genome mining has contributed to the identification of biosynthetic gene clusters, which encode enzymes that are responsible for synthesis of such secondary metabolites. Unfortunately, these large gene clusters generally remain silent or cryptic under normal laboratory settings, which creates a hurdle in identification and isolation of these compounds. Various strategies, such as changes in growth conditions and antibiotic stress, have been applied to elicit the expression of these cryptic gene clusters. Although a number of compounds have been isolated from different Burkholderia species, the mechanisms by which the corresponding gene clusters are regulated remain poorly understood. This review summarizes the activity of well characterized secondary metabolites from Burkholderia species and the role of local regulators in their synthesis, and it highlights recent evidence for the role of global regulators in controlling production of secondary metabolites. We suggest that targeting global regulators holds great promise for the awakening of cryptic gene clusters and for developing better strategies for discovery of novel antibiotics

Neurotoxicity of fluoride in ethanol fed rats: Role of oxidative stress, mitochondrial dysfunction and neurotransmitters

14-22Prolonged exposure to fluoride or alcohol affects brain. However, the understanding about their interactions and neurotoxicity following co-exposures is still poor. The present study was designed to assess oxidative stress, mitochondrial dysfunctions, acetylchonlineterase (AChE) activity, neurotransmitter levels and morphological alterations in brain of fluoride or/and ethanol fed rats. Six and eighteen month old animals received sodium fluoride (NaF, 25 mg/kg) and 30% ethanol (EtOH, 1 mL/kg) individually and in combination for 90 days. Brain showed elevation in oxidative stress with age and NaF/EtOH treatment. There was increased lipid peroxidation; decreased glutathione, total and protein thiol content; along with declined activities of superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase and glutathione-S-transferase under these conditions. Mitochondrial functions were impaired significantly with age and NaF/EtOH treatment. The activities of NADH dehydrogenase, succinate dehydrogenase and cytochrome c oxidase along with mitochondrial respiration rate were decreased whereas the levels of nitric oxide and citrulline were increased in treated animals. Administration of NaF/EtOH showed altered neurotransmitter levels and increased AChE activity in brain. The levels of dopamine and 5-hydroxytryptamine were decreased while 5-hydroxyindoleacetic acid and homovanillic acid were increased significantly. Histological examination showed morphological alterations in treated animals compared to controls. Interestingly, the observed effects were more pronounced in rats co-exposed to NaF and EtOH. It is concluded that neurotoxic effects of fluoride are age dependent and further amplified by alcohol co-administration. These effects are mediated through elevated oxidative stress, mitochondrial dysfunctions and impaired neurotransmitter functions

Tubulin Posttranslational Modifications and Emerging Links to Human Disease

International audienceTubulin posttranslational modifications are currently emerging as important regulators of the microtubule cytoskeleton and thus have a strong potential to be implicated in a number of disorders. Here, we review the latest advances in understanding the physiological roles of tubulin modifications and their links to a variety of pathologies

UrbanFly: Uncertainty-Aware Planning for Navigation Amongst High-Rises with Monocular Visual-Inertial SLAM Maps

We present UrbanFly: an uncertainty-aware real-time planning framework for quadrotor navigation in urban high-rise environments. A core aspect of UrbanFly is its ability to robustly plan directly on the sparse point clouds generated by a Monocular Visual Inertial SLAM (VINS) backend. It achieves this by using the sparse point clouds to build an uncertainty-integrated cuboid representation of the environment through a data-driven monocular plane segmentation network. Our chosen world model provides faster distance queries than the more common voxel-grid representation, and UrbanFly leverages this capability in two different ways leading to as many trajectory optimizers. The first optimizer uses a gradient-free cross-entropy method to compute trajectories that minimize collision probability and smoothness cost. Our second optimizer is a simplified version of the first and uses a sequential convex programming optimizer initialized based on probabilistic safety estimates on a set of randomly drawn trajectories. Both our trajectory optimizers are made computationally tractable and independent of the nature of underlying uncertainty by embedding the distribution of collision violations in Reproducing Kernel Hilbert Space. Empowered by the algorithmic innovation, UrbanFly outperforms competing baselines in metrics such as collision rate, trajectory length, etc., on a high fidelity AirSim simulator augmented with synthetic and real-world dataset scenes.Comment: Submitted to IROS 2022, Code available at https://github.com/sudarshan-s-harithas/UrbanFl

REACTIVE POWER COMPENSATION AND VOLTAGESTABILIZATION FOR WIND POWER IN A WEAK DISTRIBUTION NETWORK

One of the most promising alternate sources of energy is wind energy. Energy of the wind is converted to electrical energy in wind farms and is then connected to a weak distribution network to supply local loads. Most wind farms use induction generators for electricity generation. These induction generators draw excessive reactive power for their operation and this causes shortage of reactive power in the system and leads to voltage collapse. This problem is simulated on PSCAD/EMTDC platform. For static compensation, capacitor banks are used and for dynamic compensation, Static Var Compensators (SVCs) are used