Ranjeet Kumar Singh

Phosphorylation of PhoP Protein Plays Direct Regulatory Role in Lipid Biosynthesis of Mycobacterium tuberculosis

Background: PhoP is global regulator of Mycobacterium tuberculosis physiology. However, the role of phosphorylation of PhoP remains unknown. Results: PhoP activates complex lipid biosynthesis only upon phosphorylation. Conclusion: PhoP regulates lipid biosynthesis by a phosphorylation-dependent mechanism to contribute to morphology of the bacilli. Significance: This study sheds light on the unexplored role of phosphorylation of PhoP in regulating biosynthesis of lipids unique to M. tuberculosis. Mycobacterium tuberculosis PhoP is essential for virulence and intracellular growth of the tubercle bacilli. Genetic evidence suggests that PhoP regulates complex lipid biosynthesis, and absence of some of these lipid molecules in a phoP mutant partly accounts for its attenuated growth in macrophages and/or mice. To investigate the mechanism of regulation, here we demonstrate the essentiality of phosphorylation of PhoP in the regulation of complex lipid biosynthesis. We show that phosphorylated PhoP activates transcription of pks2 and msl3, gene(s) encoding polyketide β-ketoacyl synthases through direct DNA binding at the upstream regulatory region(s) of the target genes. Our results identify the genetic determinants recognized by PhoP and show that activation of target genes requires interaction(s) of the phosphorylated regulator at the cognate binding sites. The fact that these sites within the regulatory region of respective genes do not bind in vitro with either unphosphorylated or phosphorylation-deficient PhoP protein is consistent with phosphorylation-dependent assembly of the transcription initiation complex leading to in vivo transcriptional activation. Together, these results reveal so far unknown molecular mechanisms of how PhoP contributes to M. tuberculosis cell wall composition by regulating complex lipid biosynthesis.

Development of a Generalized Strategy for Dry Beneficiation of Fine Coal over a Vibrating Inclined Deck

Beneficiation of coal fines of size −1.0 + 0.1 mm using an air table under controlled fluidization was investigated. Widely different feed coals with ash values ranging from 30–50% were shown to respond well to the process. Interactions among process variables towards influencing the separation performance were studied carefully to have a firm control over the process. Detailed statistical analysis of the experimental data was carried out and in-depth understanding of the process was accomplished through various statistical plots. The preferred operating regimes were identified for three different coals to achieve maximum mass yield for targeted product qualities. Flow sheets were developed for all the three coals investigated in order to obtain multiple usable products using a maximum of four stages of operation of the air table. A generalized strategy for dry cleaning of any coal with given characteristics was developed such that application potential of the air table can be enhanced.

A transcriptional co-repressor regulatory circuit controlling the heat-shock response of Mycobacterium tuberculosis

The co‐ordinated regulation of heat shock proteins is critically important for the stress response of M. tuberculosis, failure of which results in enhanced immune recognition of the tubercle bacilli with reduced survival during chronic infections. In this study, we show that PhoP regulates the transcription of α‐crystallin 2 (acr2), expression of which increases more than any other gene of M. tuberculosis during heat‐shock or following macrophage infection. We also show that regulation of acr2 by PhoP is attributable to direct regulator‐promoter interactions at specific sites proximal to a sequence motif comprising the target site of another virulence factor, HspR. While both these regulators, on their own, are capable of influencing acr2 expression, remarkably our results show that the two virulence regulators PhoP and HspR interact with each other to influence their in vivo recruitment at the acr2 regulatory region, and in turn, contribute to stress‐specific regulation of acr2 expression. We propose a model to suggest how protein–protein interactions between PhoP and HspR influence the regulation of α‐crystallin 2, an essential pathogenic determinant of M. tuberculosis.

Recovery of Combustibles from Fine Coal through Controlled Air Fluidization over Inclined Deck

The segregation pattern for dry beneficiation of fine coal (–1.0 + 0.1 mm) in an air table was investigated. The feasibility of cleaning a high ash (~49%) coal to the ash level specified for application in a thermal power plant (34%) was established. The density (ash) distribution pattern on the deck surface at steady state established the progress of segregation under various operating conditions. The operating regimes for a desired product at suitable mass yield were identified. A strategy was developed to process the high ash thermal coal and the flow scheme was established through which around 47% mass yield of the clean coal was obtained at 34% ash level. A second product was generated which was suitable for application in a fluidized bed combustion unit. A completely rejectable tailing was also obtained with 69% ash having a mass yield of 33%. Thus, it was established that high ash coal fines can be treated efficiently by controlled air fluidization over an inclined porous deck. The present study also brought out the features of separation and how segregation progresses over the deck as the material moves towards the discharge end. The effects of important process variables on the separation performance as well as on the segregation pattern were also established.

Study of Process Efficiency for High-Ash Fine Coal Cleaning in a Kelsey Centrifugal Jig

ABSTRACT Processing of ultrafine (< 300 µm), high-ash (> 50 %) coal was investigated in a laboratory Kelsey Jig. A set of experiments were designed through design expert software. Four different process parameters were considered for the present study, including pulse frequency, spin frequency, feed flow rate, and ragging size, while other parameters were kept constant. In a single pass through a KCJ, an absolute 8% reduction in the ash with 53% yield was obtained. Statistical modeling studies and process optimization were also performed. Two different process schemes were studied to process the high-ash coal fines involving (a) a Kelsey Jig and (b) a hydrocyclone followed by a Kelsey Jig. It was observed that the removal of particles below 45 µm by a desliming process results in a reduction of 12% ash with 60% yield at the optimized condition. The Ecart probable value was estimated for particle sizes of 300 x 45 micron. The Ecart probable value 0.08 over a particle-size range of 300 µm x 45 µm with a separation density value of 1.86 is indicative of the good separation performance achievable from a Kelsey Jig for high-ash feed coal.

Enhancing the Utilization Potential of a Low Grade Chromite Ore through Extensive Physical Separation

Low grade chromite ore with less than 30% Cr2O3 was investigated with a view to enhance its utilization potential. The ore contained olivine, serpentine, and chrysotile as the gangue minerals. The chromite mineral contained alumina, magnesia, and FeO in its lattice. Critical mineralogical assessment indicated that enrichment to a level of 39-43% Cr2O3 may be possible. Beneficiation of the ore was undertaken using gravity based methods. Inadequate liberation prevented any significant enrichment at 0.9 mm top size. At 0.3 mm top size, the spiral concentration generated a concentrate with 40.5% Cr2O3 from the coarser fraction. The finer fraction was treated in a shaking table to generate another concentrate with 41.6% Cr2O3. The final combined concentrate assayed 41.2% Cr2O3 with a Cr/Fe ratio of 2.27. The middling from both treatments were rich in chromite content and were recommended to be included in the concentrates. Chromite recovery from the coarse reject was also beneficial. It was recommended that 8-10% solids content of the reject stream with 0.02 kg/t of Magnafloc flocculant may be used to achieve best settling characteristics of the reject fines.

Development of Dry Beneficiation Flow Sheet for Fine Coking Coal

ABSTRACT Flow sheet development of dry beneficiation of coking coal fines of size −1.0 + 0.1 mm using controlled vibro fluidization is the aim of the present study. Process conditions affecting the separation features on air table were identified and detailed individual effects and interaction among the process factors have been quantified. Experimental data were subjected to statistical analysis, and an in-depth understanding of the process was accomplished through various statistical plots. Optimization exercise was also carried out to find the preferred operating regimes to achieve maximum mass yield for the targeted product. Using the in-depth knowledge obtained, flow sheet was developed for coking coal investigated using a multistage operation of the air table for reducing ash in feed sample with 34.5% ash to 15.5% ash. Products in each stage are subjected to sink and float tests to understand the separation efficiency of dry beneficiation on coking coal at each stage. Petrological studies were also carried out to find the enhancement of organic matter in the beneficiated product. From all the studies and interpretations, dry coal beneficiation on coking coal gave a satisfactory result which raised the expectations of commercially using dry beneficiation of coking coal in future as a concentration technique, thereby reducing the consumption of water.