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Dive into the research topics where Rasik Ravindra is active.

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Featured researches published by Rasik Ravindra.


Research in Microbiology | 2011

Vertical distribution of bacteria in a lake sediment from Antarctica by culture-independent and culture-dependent approaches

S. Shivaji; Kiran Kumari; Kankipati Hara Kishore; Pavan Kumar Pindi; Pasupuleti Sreenivasa Rao; T. N. R. Srinivas; Rajesh Asthana; Rasik Ravindra

Bacterial diversity of the subsurface (18-22 cm), middle (60-64 cm) and bottom (100-104 cm) of a 136-cm-long sediment core sampled from a freshwater lake in Antarctica was determined by the culturable approach, T-RFLP and 16S rRNA gene clone libraries. Using the culturable approach, 41 strains were isolated and, based on phylogenetic analysis, they could be categorized into 14 groups. Representatives of the 14 groups varied in their growth temperature range (4-30 °C), in their tolerance to NaCl (0-2 M NaCl) and in the growth pH range (5-11). Eleven of fourteen representative strains exhibited either amylase, lipase, protease and (or) urease activities at 4 °C. Bacterial diversity at the phyla level using T-RFLP and 16S rRNA clone libraries was similar and clones were affiliated with Proteobacteria, Bacteroidetes, Actinobacteria and Firmicutes. TRFs affiliated with Spirochaetes were detected only by the T-RFLP approach and clones affiliated with Caldiserica only in the clone libraries. Stratification of bacteria along the depth of the sediment was observed both with the T-RFLP and the 16S rRNA gene clone library methods, and results indicated that stratification was dependent on the nature of the organism, aerobic or anaerobic. For instance, aerobic Janthinobacterium and Polaromonas were confined to the surface of the sediment, whereas anaerobic Caldisericum was present only in the bottom portion of the core. It may be concluded that the bacterial diversity of an Antarctic lake sediment core sample varies throughout the length of the core depending on the oxic-anoxic conditions of the sediment. Furthermore, these psychrophilic bacteria, due to their ability to produce extracellular cold active enzymes, might play a key role in the transformation of complex organic compounds.


Environmental Monitoring and Assessment | 2013

Atmospheric deposition studies of heavy metals in Arctic by comparative analysis of lichens and cryoconite

Shiv Mohan Singh; Jagdev Sharma; Puja Gawas-Sakhalkar; Ajay K. Upadhyay; Simantini Naik; Shailesh M. Pedneker; Rasik Ravindra

Lichens and cryoconite (rounded or granular, brownish-black debris occurring in holes on the glacier surface) from Ny-Ålesund were used for understanding the elemental deposition pattern in the area. Lichen samples collected from low-lying coastal region and cryoconite samples from high altitudinal glacier area were processed and analysed for elements such as aluminium (Al), arsenic (As), cadmium (Cd), cobalt (Co), chromium (Cr), cesium (Cs), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), lead (Pb), vanadium (V) and zinc (Zn) through inductively coupled plasma mass spectrometry. Results showed that heavy metals, Al and Fe, are present in high concentration in the cryoconite samples. Al was also present in high amounts in seven of the eight lichen samples studied. The general scheme of elements in the decreasing order of their concentrations for most of the cryoconite samples was Al > Fe > Mn > Zn > V > Pb > Cr > Ni > Cu > Co > As > Cs > Cd while that for the lichen samples was Al > Fe > Zn > Mn > Pb > Cu > Cs > Cr > Ni > V > Co > As > Cd. Similarity in trends in the two sample types confirms that the environment indeed contains these elements in that order of concentration which overtime got accumulated in the samples. Overall comparison showed most elements to be present in high concentrations in the cryoconite samples as compared to the lichen samples. Within the lichens, elemental accumulation data suggests that the low-lying site (L-2) from where Cladonia mediterranea sample was collected was the most polluted accumulating a number of elements at high concentrations. The probable reasons for such deposition patterns in the region could be natural (crustal contribution and sea salt spray) and anthropogenic (local and long-distance transmission of dust particles). In the future, this data can form a baseline for monitoring quantum of atmospheric heavy metal deposition in lichens and cryoconite of Svalbard, Arctic.


The Holocene | 2011

Nitrate records of a shallow ice core from East Antarctica: Atmospheric processes, preservation and climatic implications

C. M. Laluraj; Meloth Thamban; Sushant S. Naik; B.L. Redkar; Arun Chaturvedi; Rasik Ravindra

High-resolution records of nitrate (NO3 −), oxygen isotope (δ 18O) and non-sea salt sulphate (nssSO4 2− ) were studied using an ice core collected from central Dronning Maud Land in East Antarctica to identify the influence of environmental variability on accumulation of NO3 − over the past 450 years. The results confirmed that multiple processes were responsible for the production and preservation of NO3 − in Antarctic ice. Correlation between NO3 − and nssSO4 2− peaks revealed that sulphate aerosols released during major volcanic eruptions might have activated the production of nitric acid, which was scavenged by ion-induced nucleation in polar ice sheets. The correlation between the nitrate and δ18 O records further suggest that enhanced NO3 − preservation in the ice occurred during periods of lower atmospheric temperature. Major shifts in the NO3 − record of the ice core presently studied and its comparison with 10Be record from a core collected from South Pole suggest that a reduction in solar activity influenced the NO3 − accumulation in Antarctica through enhanced production of odd nitrogen species.


Polar Research | 2011

Phosphate solubilizing ability of two Arctic Aspergillus niger strains

Shiv Mohan Singh; Lal S. Yadav; Sanjay K. Singh; Purnima Singh; Paras N. Singh; Rasik Ravindra

Many filamentous fungi were isolated from the soils of Ny-Ålesund, Spitsbergen, Svalbard, and were screened in vitro for their phosphate solubilizing ability. Two strains of Aspergillus niger showed good tricalcium phosphate (TCP) solubilizing ability in Pikovskayas medium. The TCP solubilization index was calculated at varying levels of pH and temperatures. The ability of Aspergillus niger strain-1 to solubilize and release inorganic-P was 285 µg ml–1, while Aspergillus niger strain-2 solubilized 262 µg ml–1 from 0.5% TCP after seven days. This is the first report of TCP solubilization by Arctic strains that may serve as very good phosphate solubilizers in the form of biofertilizer.


Natural Products and Bioprospecting | 2012

Antimicrobial activity of PVP from an Antarctic bacterium, Janthinobacterium sp. Ant5-2, on multi-drug and methicillin resistant Staphylococcus aureus

Jonathan P. Huang; Nazia Mojib; Rakesh R. Goli; Samantha Watkins; Ken B. Waites; Rasik Ravindra; Dale T. Andersen; Asim K. Bej

Multiple drug resistant (MDR) and methicillin-resistant Staphylococcus aureus (MRSA) have become increasingly prevalent as a community acquired infection. As a result limited treatment options are available with conventional synthetic antibiotics. Bioprospecting natural products with potent antimicrobial activity show promise for developing new drugs against this pathogen. In this study, we have investigated the antimicrobial activity of a purple violet pigment (PVP) from an Antarctic bacterium, Janthinobacterium sp. Ant5-2 on 15 clinical MDR and MRSA strains. The colorimetric resazurin assay was employed to determine the minimum inhibitory concentration (MIC90) of PVP against MDR and MRSA. The MIC90 ranged between 1.57 µg/mL and 3.13 µg/mL, which are significantly lower than many antimicrobials tested from natural sources against this pathogen. The spectrophotometrically determined growth analysis and total microscopic counts using Live/dead® BacLight™ fluorescent stain exhibited a steady decrease in viability of both MDR and MRSA cultures following treatment with PVP at the MIC levels. In silico predictive molecular docking study revealed that PVP could be a DNA-targeting minor groove binding antimicrobial compound. The continued development of novel antimicrobials derived from natural sources with the combination of a suite of conventional antibiotics could stem the rising pandemic of MDR and MRSA along with other deadly microbial pathogens.


Environmental Monitoring and Assessment | 2009

Origin and characterisation of microparticles in an ice core from the Central Dronning Maud Land, East Antarctica

C. M. Laluraj; K. P. Krishnan; Meloth Thamban; Rahul Mohan; Sushant S. Naik; Witty D’Souza; Rasik Ravindra; Arun Chaturvedi

The scanning electron microscopy–energy dispersive spectroscopic (SEM–EDS) study of selected samples from an ice core collected from Central Dronning Maud Land (CDML), East Antarctica, revealed several microparticles. They are mainly siliceous and carbonaceous particles and have distinct variations in their shape and composition. The morphology and major element chemistry of the particles suggest their origin from either volcanic eruptions or continental dust. The EDS analysis revealed that the volcanic particles are enriched in silica (average SiO2 62%), compared to the continental dust particle (average SiO2 56%). We found that the tephra relating to Agung (1963) and Karkatau (1883) volcanic eruptions, as recorded, in the ice core harbored microbial cells (both coocoid and rods). The occurrence of organic and inorganic particles which bear relation to volcanic eruption and continental dust implies significant environmental changes in the recent past.


Polar Research | 2012

High-temperature optima phosphatases from the cold-tolerant Arctic fungus Penicillium citrinum

Puja Gawas-Sakhalkar; Shiv Mohan Singh; Naik Simantini; Rasik Ravindra

Fifty-six fungal isolates from Arctic soils were subjected to primary screening for their ability to solubilize insoluble inorganic phosphate. Nine of the isolates were further analysed quantitatively for phosphatase production using para-nitrophenylphosphate as substrate. Amongst these, a cold-tolerant fungus, Penicillium citrinum strain PG162 was found to be the best producer of intracellular acid phosphatase. Further characterization of the enzyme showed that it is most active in the temperature range of 40–60°C and pH range of 4.2–4.8. The dried enzyme extract is stable at a temperature of up to 50°C for at least 1 h. Its activity is affected by presence of metal ions. Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS–PAGE) analysis suggests the molecular weight of the enzyme to be between 20 and 29 kDa. The present study is important with respect to our understanding of the kind of enzymatic reactions that take place in the polar microbes, and the extent to which their activity is sustained.


Polar Record | 2015

Elemental composition and bacterial incidence in firn-cores at Midre Lovénbreen glacier, Svalbard

Shiv Mohan Singh; Puja Gawas-Sakhalkar; Simantini Naik; Rasik Ravindra; Jagdev Sharma; Ajay Kumar Upadhyay; Ravindra Uttam Mulik; Priyanka Bohare

The present study was conducted to measure the elemental concentration and bacterial deposition in the firn-cores at the Midre Lovenbreen glacier, Svalbard. Firn-cores up to 1m deep were collected and divided into three subsections. These were subjected to elemental analysis using inductively coupled plasma mass spectroscopy (ICPMS). In all 20 elements were analysed. The crustal enrichment factors calculated for these elements on the basis of Fe values, demonstrate that the elements have derived from both crustal and anthropogenic sources. For certain elements there also exists a possibility of input from sea salt spray. Total bacterial counts in these firn samples ranged from 1.03 × 10 5 to 3.67 × 10 5 per ml of meltwater. Culturability of these bacterial cells, in comparison to the total count was very low. At 4°C the maximum culturability was


Archive | 2013

Impact of Climate Change on Lichen and Moss Communities in Ny-Ålesund, Arctic: Some Preliminary Observations

Shiv Mohan Singh; Rasik Ravindra

The information on community structure of lichens and mosses, and their distribution in Ny-Alesund Arctic is a thrust area for investigation. There were four prominent areas bearing the different communities in Ny-Alesund. Climate change is beginning to cause large-scale changes in Ny-Alesund. Due to increase in summer temperature and glacial retreat in particular, fresh area is exposed for colonisation and succession of new community in the areas.


Archive | 2013

Antarctic Climate Variability During the Past Few Centuries Based on Ice Core Records from Coastal Dronning Maud Land and Its Implications on the Recent Warming

Meloth Thamban; Sushant S. Naik; C. M. Laluraj; Arun Chaturvedi; Rasik Ravindra

Instrumental and proxy records have revealed that the Antarctic climate system experienced remarkable changes in the past. In order to reconstruct the recent Antarctic climate change during the past centuries with annual to seasonal resolution and to understand its spatial variability, two well-dated ice cores (IND-22/B4 – 62 m and IND-25/B5 – 65 m) from the coastal Dronning Maud Land region of East Antarctica were studied for stable oxygen and hydrogen isotope ratio variability. Of these, the IND-25/B5 provided high-resolution records of the past 100 years (1905–2005) and the IND-22/B4 core represented the past ~470 years (1530–2002) of climate change. The considerable variations in δ18O records on an interannual to decadal scale seems to be associated with changes in low and mid latitude climatic modes like the Southern Annular Mode (SAM) and El Nino Southern Oscillation (ENSO). The extended records of IND-22/B4 exhibited relatively more negative δ18O values during periods of reduced solar activity like the Dalton and Maunder Minima, indicating manifestations of solar activity on Antarctic climate. The estimated surface air temperatures using the δ18O profiles of two ice cores revealed a significant warming by 0.6–1°C per century, with greatly enhanced warming during the past several decades (~0.4°C per decade). Complimentary to the recent findings, it is proposed that the coastal areas of Dronning Maud Land are experiencing significant warming in the recent centuries and further support for a detailed evaluation on actual rates of Antarctic warming through a combination of instrumental and proxy records.

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Dive into the Rasik Ravindra's collaboration.

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Shiv Mohan Singh

National Centre for Antarctic and Ocean Research

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Abhijit Mazumder

Birbal Sahni Institute of Palaeobotany

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Pawan Govil

National Centre for Antarctic and Ocean Research

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Rahul Mohan

National Centre for Antarctic and Ocean Research

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Meloth Thamban

National Centre for Antarctic and Ocean Research

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Puja Gawas-Sakhalkar

National Centre for Antarctic and Ocean Research

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Rajesh Asthana

Geological Survey of India

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Arun Chaturvedi

Geological Survey of India

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C. M. Laluraj

National Centre for Antarctic and Ocean Research

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Jagdev Sharma

Indian Council of Agricultural Research

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