Low iron availability in the host upregulates the mbt gene cluster of Mycobacterium tuberculosis, which is responsible for mycobactin biosynthesis. However, the biological significance of mycobactins in the growth of this pathogen and in disease progression has not been elucidated. We have disrupted the mbtE gene (Rv2380c) in the mbt cluster to evaluate the importance of mycobactin biosynthesis in the growth and virulence of M. tuberculosis. The mbtE mutant (MtbΔmbtE) was unable to synthesize mycobactins, displayed an altered colony morphology, and was attenuated for growth in broth culture and in macrophages. Transmission electron microscopy revealed that MtbΔmbtE displayed an altered cell wall permeability. The growth characteristics and colony morphology of MtbΔmbtE were similar to wild type when the medium was supplemented with mycobactins or when MtbΔmbtE was genetically complemented with the mbtE gene. Moreover, guinea pigs infected with MtbΔmbtE exhibited a significantly reduced bacillary load and histopathological damage in the organs, in comparison to M. tuberculosis-infected animals.This study highlights the importance of mycobactins in the growth and virulence of M. tuberculosis and establishes the enzymes of mycobactin biosynthesis as novel targets for the development of therapeutic interventions against tuberculosis.
Yttria stabilized Zirconia (YSZ) pellets with different crystallite sizes were irradiated with 80 MeV Ag$^{6+}$ ions at room temperature and 1000 K to understand the role of crystallite size/material microstructure and irradiation temperature on the radiation tolerance against high electronic energy loss (S$_e$). X-ray diffraction and Raman spectroscopy measurements reveal that, irrespective of the irradiation temperature, the nano-crystalline samples suffered more damage as compared to the bulk-like sample. A reduction in the irradiation damage i.e. improvement in the radiation tolerance, was observed for all the samples irradiated at 1000 K. The reduction in the damage, however, was remarkably higher for the two nano-crystalline samples compared to the bulk-like sample, and hence the difference in the damage between the bulk-like and nano-crystalline samples was also significantly lower at 1000 K than that at room temperature. The irradiation damage, against S$_e$, was thus found to be critically dependent on the interplay between the irradiation temperature and crystallite size. These results are explained with the help of detailed theoretical calculations/simulations based on the 'in-elastic thermal spike' model by taking into consideration the combined effect of crystallite size and environmental (irradiation) temperature on the electron-phonon coupling factor and lattice thermal conductivity (and hence on the resulting thermal spike). Our results are crucial from the fundamental perspective of comprehending the size and temperature dependent radiation damage against S$_e$ ; and also for a number of applications, in various radiation environments, where nano-materials are being envisioned for use.
One of the important determinants of virulence of Mycobacterium tuberculosis is adaptation to adverse conditions encountered in the host cells. The ability of Mycobacterium to successfully adapt to stress conditions is brought about by the expression of specific regulons effected by a repertoire of sigma factors. The induction and availability of sigma factors in response to specific stimuli is governed by a complex regulatory network comprising a number of proteins, including sigma factors themselves. A serine-threonine protein kinase-mediated signaling pathway adds another dimension to the mycobacterial sigma factor regulatory network. This review highlights the recent advances in understanding mycobacterial sigma factors, their regulation and contribution to bacterial pathogenesis.
Tuberculosis (TB) is one of the most challenging global health problems. BCG, the only vaccine in use against TB, has not performed satisfactorily and most efforts to develop a new TB vaccine have met with little success.In this review, without revisiting the stories of failed TB vaccines, we focus on what has prevented the development of a perfect TB vaccine and issues that need immediate attention in order to succeed.
Background The failure of Mycobacterium bovis Bacille Calmette-Guérin to impart satisfactory protection against adult pulmonary tuberculosis has necessitated the development of more effective TB vaccines. The assumption that the vaccine strain should be antigenically as similar as possible to the disease causing pathogen has led to the evaluation of M.tuberculosis mutants as candidate tuberculosis vaccines. Methods/Principal Findings In this study, we have generated a mutant of M.tuberculosis (Mtb∆mms) by disrupting 3 virulence genes encoding a mycobacterial secretory acid phosphatase (sapM) and two phosphotyrosine protein phosphatases (mptpA and mptpB) and have evaluated its protective efficacy in guinea pigs. We observed that Mtb∆mms was highly attenuated in THP-1 macrophages. Moreover, no bacilli were recovered from the lungs and spleens of guinea pigs after 10 weeks of Mtb∆mms inoculation, although, initially, the mutant exhibited some growth in the spleens. Subsequently, when Mtb∆mms was evaluated for its protective efficacy, we observed that similar to BCG vaccination, Mtb∆mms exhibited a significantly reduced CFU in the lungs of guinea pigs when compared with the unvaccinated animals at 4 weeks after challenge. In addition, our observations at 12 weeks post challenge demonstrated that Mtb∆mms exhibited a more sustainable and superior protection in lungs as compared to BCG. However, the mutant failed to control the hematogenous spread as the splenic bacillary load between Mtb∆mms vaccinated and sham immunized animals was not significantly different. The gross pathological observations and histopathological observations corroborated the bacterial findings. Inspite of disruption of phosphatase genes in MtbΔmms, the lipid profiles of M.tuberculosis and MtbΔmms were identical indicating thereby that the phenotype of the mutant was ascribed to the loss of phosphatase genes and the influence was not related to any alteration in the lipid composition. Conclusions/Significance This study highlights the importance of M.tuberculosis mutants in imparting protection against pulmonary TB.
We present results from an electromagnetic scanning survey acquired to assess the prospectivity of a large deepwater frontier area for which only sparse 2D seismic data were available. Fast track processing of the scanning data revealed a regional trend on which a resistive anomaly is overlaid. Using 1D inversion and analysis of higher frequency, small offset data, the anomaly was interpreted to be an expression of resistivity variations in the shallow subsurface, which may be masking interesting anomalies from deeper geological features. To reduce the effect of the shallow resistive features and remove the regional trend, a novel approach called reference modeling has been applied. The idea of reference modeling is to compute normalized fields relative to a background model describing the shallow and regional resistivity variations, as well as bathymetric changes. The results obtained significantly increased our confidence in our interpretation of the scanning data and revealed three interesting resistive anomalies likely at depth that may be considered potential targets for further geophysical investigation.
SummaryIndia has developed an ambitious research program after successfully unearthing gas hydrate layer at site 10 in Krishna Godavari (KG) Offshore, during first National Gas Hydrate Program (NGHP-1). After studying the result from NGHP-1, second NGHP has been firmed up with an objective to identify the Gas Hydrate prospect for test drilling using seismic data and well analysis in KG offshore areas.First time a 3D seismic data volume has been studied with objective to identify Gas Hydrate prone areas in Indian water.To achieve this objective seismic data has been calibrated with well log to identify the Top and bottom of Gas Hydrate Stability Zone. The extent of Gas hydrate is inferred on seismic section by large amplitude (opposite polarity of with respect to Sea bottom) bottom simulating reflector (BSR), which is following the sea bottom and also at places cutting across dipping srata. In this study, the BSR mapped and then RMS amplitude extracted within window of 100ms above of it. RMS amplitude distribution suggests the variance in Gas hydrate concentration spatially primarily guided by the porosity variation in shape of channel and scroll bar. Further RMS amplitude extraction 20 ms below BSR suggest the presence of free gas areas associated with Gas hydrate in the down dip towards the regional lows.The study concludes that there are three to four areas where positive acoustic impedance within GHSZ is available, probably indicative of high Gas Hydrate concentration due to better reservoir condition and may be tested.
Iron is one of the crucial elements required for the growth of Mycobacterium tuberculosis. However, excess free iron becomes toxic for the cells because it catalyzes the production of reactive oxygen radicals, leading to oxidative damage. Hence, it is essential for the pathogen to have the ability to store intracellular iron in an iron-rich environment and utilize it under iron depletion. M. tuberculosis has two iron storage proteins, namely BfrA (Rv1876; a bacterioferritin) and BfrB (Rv3841; a ferritin-like protein). However, the demonstration of biological significance requires the disruption of relevant genes and the evaluation of the resulting mutant for its ability to survive in the host and cause disease. In this study, we have disrupted bfrA and bfrB of M. tuberculosis and demonstrated that these genes are crucial for the storage and supply of iron for the growth of bacteria and to withstand oxidative stress in vitro. In addition, the bfrA bfrB double mutant (H37Rv ΔbfrA ΔbfrB) exhibited a marked reduction in its ability to survive inside human macrophages. Guinea pigs infected with H37Rv ΔbfrA ΔbfrB exhibited a marked diminution in the dissemination of the bacilli to spleen compared to that of the parental strain. Moreover, guinea pigs infected with H37Rv ΔbfrA ΔbfrB exhibited significantly reduced pathological damage in spleen and lungs compared to that of animals infected with the parental strain. Our study clearly demonstrates the importance of these iron storage proteins in the survival and pathogenesis of M. tuberculosis in the host and establishes them as attractive targets for the development of new inhibitors against mycobacterial infections.
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