Indian researchers reverse multidrug resistance in E. coli

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(From left) Dr. Saurabh Mishra, Dr. Amit Singh and Prashant Shukla of IISc have been able to make drug-resistant E. coli become sensitive to antibiotics by inhibiting hydrogen sulphide synthesis.

Indian researchers have unravelled the mechanism by which hydrogen sulphide (H2S) gas produced by bacteria protects them from antibiotics and plays a key role in helping bacteria develop drug resistance. And by blocking/disabling the enzyme that triggers the biosynthesis of hydrogen sulphide in bacteria, the researchers from Bengaluru’s Indian Institute of Science (IISc) and Indian Institute of Science Education and Research (IISER) Pune have been able to reverse antibiotic resistance in E. coli bacteria; E. coli bacteria were isolated from patients suffering from urinary tract infection. The results were published in the journal Chemical Science.

Antibiotics kill by increasing the levels of reactive oxygen species (oxidative stress) inside bacterial cells. So any mechanism that detoxifies or counters reactive oxygen species generated by antibiotics will reduce the efficacy of antibiotics. “Hydrogen sulphide does this to nullify the effect of antibiotics,” says Dr. Amit Singh from the Department of Microbiology and Cell Biology at IISc and one of the corresponding authors of the paper. “When bacteria face reactive oxygen species a protective mechanism in the bacteria kicks in and more hydrogen sulphide is produced.” Hydrogen sulphide successfully counters reactive oxygen species and reduces the efficacy of antibiotics.

There was nearly 50% reduction in drug-resistance when hydrogen sulphide production was blocked.The researchers carried out simple experiments to establish this. They first ascertained that regardless of the mode of action of antibiotics, the drugs uniformly induce reactive oxygen species formation inside E. coli bacteria. Then to test if increased levels of hydrogen sulphide gas inside bacteria counter reactive oxygen species produced upon treatment with antibiotics, a small molecule that produces hydrogen sulphide in a controlled manner inside the bacteria was used. “Hydrogen sulphide  released by the molecule was able to counter reactive oxygen species and reduce the ability of antibiotics to kill bacteria,” says Dr. Singh.

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Prof. Harinath Chakrapani’s team at IISER Pune synthesised the small molecule.

The small molecule was synthesised by a team led by Prof. Harinath Chakrapani from the Department of Chemistry, IISER, Pune; he is one of the corresponding authors of the paper. “We designed the small molecule keeping in mind that synthesis should be easy, efficiency in producing hydrogen sulfide should be high and the molecule should release hydrogen sulfide only inside bacteria and not mammalian cells,” says Vinayak S. Khodade from the Department of Chemistry, IISER, Pune and one of the authors of the paper who contributed equally like the first author. The researchers were able to selectively increase hydrogen sulphide levels inside a wide variety of bacteria.

To reconfirm hydrogen sulphide’s role in countering reactive oxygen species, the team took multidrug-resistant, pathogenic strains of E. coli from patients suffering from urinary tract infection and measured the hydrogen sulphide levels in these strains. “We found the drug-resistant strains were naturally producing more hydrogen sulphide compared with drug-sensitive E. coli,” says Prashant Shukla from the Department of Microbiology and Cell Biology at IISc and the first author of the paper. So the team used a chemical compound that inhibits an enzyme responsible for hydrogen sulphide production. “There was nearly 50% reduction in drug-resistance when hydrogen sulphide production was blocked,” Dr. Singh says.

“Bacteria that are genetically resistant to antibiotics actually become sensitive to antibiotics when hydrogen sulphide synthesis is inhibited,” says Prof. Chakrapani. The multidrug-resistant E. coli regained its ability to survive antibiotics when hydrogen sulphide was once again supplied by introducing the small molecule synthesised by Prof. Chakrapani.

“As a result of our study, we have a found new mechanism to develop a new class of drug candidates that specifically target multidrug-resistant bacteria,” says Prof. Chakrapani. The researchers already have a few inhibitors that seem capable of blocking hydrogen sulfide production. But efforts are on to develop a library of inhibitors to increase the chances of success.

How H2S acts

The researchers identified that E. coli has two modes of respiration involving two different enzymes. The hydrogen sulfide gas produced shuts down E. coli’s aerobic respiration by targeting the main enzyme (cytochrome bo oxidase (CyoA)) responsible for it. E. coli then switches over to an alternative mode of respiration by relying on a different enzyme — cytochrome bd oxidase (Cydb). Besides enabling respiration, the Cydb enzyme detoxifies the reactive oxygen species produced by antibiotics and blunts the action of antibiotics.

“So we found that hydrogen sulfide activates the Cydb enzyme, which, in turn, is responsible for increasing resistance towards antibiotics,” says Dr. Singh. “If we have a drug-like molecule(s) that blocks hydrogen sulfide production and inhibits Cydb enzyme activity then the combination will be highly lethal against multidrug-resistant bacteria.” This combination can also be used along with antibiotics to effectively treat difficult-to-cure bacterial infections.

The link between hydrogen sulfide and Cydb enzyme in the emergence of drug resistance is another key finding of the study.

Published in The Hindu on May 6, 2017

Pune researchers fabricate a flexible nanogenerator for wearable electronics

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Prof. Satishchandra Ogale (left) of IISER Pune and Dipti Dhakras of NCL Pune have produced a nanogenerator that produces 14 volts and 28 microwatt per square cm when thumb pressure is applied.

Producing wearable electronics that uses a portable nanogenerator which generates electric power when pressure or twist is applied got a shot in the arm, thanks to research carried out by Pune researchers. The nanogenerator, which was fabricated by them, produced 14 volts when thumb pressure was applied. The results were published recently in the journal Advanced Materials & Interfaces.

To demonstrate the potential of the nanogenerator to power small electronic devices, pressure equivalent to thumb pressure was continuously exerted on the nanogenerator for 20 minutes by using a vibration producing motor. About 28 micro watt per square cm power and 14 volt that was generated was stored in a capacitor and used for charging a mobile phone.

Currently, there is considerable research emphasis to develop flexible or wearable devices. Such devices should be portable, lightweight, shock resistant, and inexpensive. And the devices should ideally be powered by harvesting easily available mechanical or vibration energy, making battery or related wiring redundant. Piezoelectric materials, which can generate electrical power locally through stress or flexing, are a great proposition in this regard.

To produce the nanogenerator, researchers from Pune’s Indian Institute of Science Education and Research (IISER) and the National Chemical Laboratory electrospun a piezoelectric polymer [P(VDF-TrFE)] directly onto a flexible, conducting carbon cloth. The carbon cloth was produced by the researchers by heating a piece of cotton cloth at 800 degree C for several hours in an inert atmosphere.

To improve the piezovoltage of the polymer fibres, the researchers coated the fibres with a stronger, inorganic ferroelectric material (BaTiO3) paste. “The nanoparticles from the coating helps fill the gaps between the polymer nanofibres and increase the piezoelectric property,” says Prof. Satishchandra Ogale from the Department of Physics and Centre for Energy Science, IISER Pune and the corresponding author of the paper. In addition, the ferroelectric material was also incorporated into the polymer to further enhance the piezoelectric property. This was done right when the polymer was electrospun.

The amount of BaTiO3 fibre incorporated into the polymer had to be optimised at 5 per cent. When the fibre density was less inside the polymer the density of interfaces (where the separation of positive and negative charges takes place) formed between the fibre and the polymer was also less. But flexibility was reduced when too much was added and it also led to more internal charging resulting in electrical short.

The coated polymer was covered by another piece of flexible carbon cloth before the device was sealed. The carbon cloth on either side of the device acted as two electrodes. The carbon cloth too contributes to the enhanced piezovoltage generated by the nanogenerator through its peculiar morphology as a substrate.

“The cloth has a surface microstructure which produces good bonding between the cloth (electrode) and the active layer. The bonding will be poor in the case of a metal layer,” says Prof. Ogale. “Due to the roughness of the cloth surface, when you press or flex the device the applied force is transmitted along different directions of the piezoelectric active layer. And this improves the piezoelectric property of the nanogenerator.” If the electrode were a flat metallic surface then the force applied would be transmitted in only one direction.

“When thumb pressure was applied on the polymer alone 2-3 volt was produced. In the case of the polymer with BaTiO3 coating the piezovoltage generated was 7-8 volt. But 14 volt was produced when BaTiO3 was incorporated into the polymer and also coated on the fibre surface,” says Dipti Dhakras from NCL and the first author of the paper.

“The voltage of 14 volt with a current of several microamperes is the highest power output reported for wearable type of nanogenerator using conducting cloth as the electrode,” notes the paper.

Published in The Hindu on November 13, 2016

IISER Pune researchers turn insulating MOFs into semiconductors

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(From left) Dr. Nirmalya Ballav, Vikash Kumar and Barun Dhara of the Indian Institute of Science Education and Research team that achieved the feat.

After four years of intensive screening, researchers at Pune’s Indian Institute of Science Education and Research (IISER) have transformed insulating metal-organic frameworks (MOFs), which are generally used for gas storage and solvent separation, into semiconductor MOFs by incorporating polymers.

A team led by Dr. Nirmalya Ballav from the Department of Chemistry at IISER Pune has converted a cadmium-based MOF insulator into a semiconductor at room temperature through nanochemistry. The electrical conductivity increased nine-fold (a billion-fold increase) when chains of conducting polymers were introduced into the nanochannels of MOFs. The results were published recently in The Journal of Physical Chemistry Letters.

Initially, the pores of metal-organic frameworks are loaded with pyrrole monomers, which are not electrical conductors. The addition of iodine brings about an oxidation reaction and converts the monomers into polymers. Unlike monomers, polymers are electrically conducting in nature and this helps turn the metal-organic framework into a semiconductor.

The weak interaction between the MOF and the conducting polymer is the key behind the unusual increase in conductivity.“The size of the pyrrole monomer nearly matches the dimension of nanochannels of the metal-organic framework. So no branch polymer was formed but only a single-chain (linear) polymerisation took place,” says Dr. Ballav. “Branch polymers are generally less electrically conducting in nature than single-chain polymers.”

The amount of polymer loaded inside the one-dimensional MOF pores was only about 10 per cent. Though electrical conductivity may increase if more polymer is packed inside the pores, the restricted diffusion in the pore nanospace does not allow more polymers to be loaded.

The MOF continued to retain its fluorescence even after becoming electrically conducting. “If you bring about electrical conductivity in a fluorescent MOF the fluorescence is expected to vanish. But it was not so in our case,” he says. “It indicates the weak, non-covalent interaction between the conducting polymer and the MOF. The weak interaction was sufficient enough for the electrons to flow across the material and is the key behind the unusual increase in conductivity.”

“The unusual enhancement of electrical conductivity of the MOF was due to the presence of conducting polymer and the electronic interaction between the MOF and the polymer,” says Barun Dhara of IISER Pune and the first author of the paper.

“Conductivity and fluorescence is a rare combination that could provide a route towards multifunctonal MOFs suitable for optoelectronics, including solar cells and imaging devices,” says a news item in Chemistry World.

Though the researchers have been able to produce a nine-fold increase in the electrical conductivity of the MOF-nanocomposite, it is still far less than silicon. “But our work shows promise that organic materials can be used in electronic industry where silicon is primarily used. It will be an economic approach for the development of future electronic applications,” says Dr. Ballav.

By using a right combination of MOFs and conducting polymer, Dr. Ballav is confident of designing nanocomposites for specific purposes. The team is working on other monomers such as aniline and thiophene.

The hybrid nanocomposite can be used for fabricating electronic devices for gas sensing applications and for making electrochemical devices such as super capacitors, he says.

Published in The Hindu on November 1, 2016.

IISER Pune researcher produces stable, inorganic, nanocrystal solar cells

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Abhishek Swarnkar (left) made the all-inorganic perovskite stable at ambient temperature by reducing the size of the crystals to nanometre range.

In a first, Abhishek Swarnkar, a research scholar from the Department of Chemistry, Indian Institute of Science Education and Research (IISER), Pune, has successfully produced a stable, high-efficiency, all-inorganic perovskite nanocrystal solar cells. The new material has 10.77 per cent efficiency to convert sunlight to electricity. The results were published on October 7 in the journal Science.

Swarnkar carried out research for six months (November 2015 to April 2016) as an intern at the National Renewable Energy Laboratory, Colorado, U.S. In 2014, he was selected for the Bhaskara Advanced Solar Energy Fellowship from the Government of India’s Department of Science and Technology (DST) and Indo-US Science and Technology Forum (IUSSTF).

Traditional research has centred around a hybrid organic-inorganic halide perovskite material. Though the hybrid material has high efficiency of over 22 per cent, the organic component in it is volatile and becomes completely unstable at ambient conditions within a short span of time. This renders the material unsuitable for commercial photovoltaic applications.

So Swarnkar replaced methyl ammonium, which is the organic component, with cesium to produce an all-inorganic perovskite material of cesium lead iodide.

The nanometer-sized perovskite crystals absorb visible sunlight (400-700 nm) at ambient temperature.“Though the completely inorganic material is stable, there are other problems. In bulk form (bigger size crystals), the cesium lead iodide perovskite absorbs sunlight light only up to about 400 nm. So it does not have much application as a photovoltaic material,” says Swarnkar.

One way of making the bulk material capable of absorbing the entire range of visible sunlight (400-700 nm) is by heating it to 300 degree C so that is attains a desirable crystal structure (cubic phase). But the problem is when the material cools down to ambient temperature, where photovoltaics normally operate, it once again regains its undesired crystal structure (orthorhombic phase) and loses the ability to absorb sunlight beyond 400 nm.

“We found that by reducing the size of the crystals to nanometre range, the material at ambient temperature is able to absorb visible sunlight till 700 nm. This is because the material retains the desirable crystal structure (cubic phase) even at room temperature,” he says. The nanocrystals were found to be stable from -196 degree C to about 200 degree C.

By reducing the size of material to nanometer range, the surface to volume ratio increases tremendously.  As a result, high surface energy comes into play and makes the high-temperature cubic phase crystal structure stable even at room temperature.

The researchers assembled the nanocrystals as a thin film. The thin film was used for making both solar cells and red LEDs. Solar cells made using the nanocrystal thin film has 10.77 per cent efficiency to convert sunlight to electricity and produce a high voltage of 1.23 volts.

“Generally, more electrical energy is required to get low energy emission in LEDs. But less electrical energy (voltage) was sufficient to produce red light in LEDs made using our method,” Swarnkar says.

Earlier at IISER, Swarnkar had worked on caesium lead bromide perovskite and published a paper in November 2015 in the journal Angewandte Chemie. “I had demonstrated that the optical properties of the material is good for display technology such as LED,” he says. “So at NREL I proposed to work on caesium lead iodide and formed a team of eight people.”

Published in The Hindu on October 10, 2016

Indian researchers’ membrane to solve marine oil spills

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The membrane developed by Soumya Mukherjee (left), Dr. Sujit Ghosh of IISER, Pune and others has a water contact angle of 176 degrees and oil contact angle of zero.

Researchers from the Indian Institute of Science Education and Research (IISER) Pune, the Central Salt & Marine Chemicals Research Institute (CSMCRI), Bhavnagar and the National Chemical Laboratory (NCL), Pune have developed a membrane with exceptional hydrophobic and extremely high oil-loving (oleophilic) properties.  The membrane can potentially be used for tackling the globally challenging issue of marine oil spills.

Such is the hydrophobic nature of the synthesised metal-organic framework (MOF) that the water contact angle is nearly 176 degrees — the “first example of an ultrahydrophobic MOF”.  At the same time, the MOF membrane has a superior affinity for oil (oleophilicity) with an oil contact angle of nearly zero degree. The results were published in the journal Chemistry – A European Journal.  

“The membrane was fabricated by mixing bulk MOF material with a binder and solvent and spray coated onto an inexpensive polypropylene substrate.  The substrate is stable in organic solvent,” says Ankit M. Kansara from CSMCRI and one of the authors of the paper. “The membrane is 100-120 micrometre in thickness.”

oil-spill-photo-optimized“The MOF is inherently ultra-microporous in nature and the porosity is retained when the thin film-like membrane is formed on the matrix. Because of the highly porous nature of the material, the coated MOF’s surface area is as high as 1,000 metre sq per gram,” says Soumya Mukherjee from IISER and the first author of the paper.

The ultrahydrophobicity was achieved by synthesising the MOF with a high density of fluorine; fluorine is inherently hydrophobic in nature and any material that is fluorine-rich becomes hydrophobic. By virtue of being highly hydrophobic, the MOF membrane, by default, becomes distinctly oleophilic or oil-loving in nature. (VIDEO: Extreme water repellency test) The marked influence of fluorines was strongly supported by theoretical insights provided by Dr. Arnab Mukherjee from IISER and a coauthor of the paper.

“The use of more fluorine makes the MOF water stable. Water stability is a prima facie criterion for industrial applications and being environmentally benign,” says Mr. Mukherjee.

When water-oil mixture is passed through the membrane the oil permeates by rapid absorption, while water is retained above the membrane. (VIDEO: Water (orange colour) and oil (colourless) separation experiment) “The oil permeation was 100 per cent in the case of an oil-water mixture,” says Dr. Sujit K. Ghosh from IISER and the corresponding author of the paper. “So if you put the membrane in an oil-water mixture, it can perfectly separate oil from water. The membrane acts like a filter.”

Water-oil emulsification takes place in the sea when water gets mixed with oil under high water current conditions. “It is very difficult to separate oil and water from an emulsion.  So in another experiment, the oil was completely separated from water when we passed the water-oil emulsion through the membrane,” says Mr. Mukherjee. (VIDEO: Water-oil emulsion separation experiment)  The emulsion droplets demulsified at the very instant it touched the membrane, and oil passed through while water was wholly retained above the membrane. The separation of water-oil emulsion was totally driven by gravity with no external force applied.

The best part is the recyclability traits of the membrane. When external mechanical force in the form of ultrasonic waves is applied in the presence of a hydrophobic organic solvent, the constituents of oil come out of the pores of the oil-saturated membrane. “The oil tends to come out due to the presence of competing hydrophobic molecules during the ultrasonification process lasting 30-60 minutes, depending on the size of the membrane and volume of oil absorbed,” says Mr. Mukherjee. The membrane is then heated at 70 degree C to remove the organic solvent and quickly regenerate the MOF. The organic solvent tends to evaporate after some time, even if the membrane is not heated.

“There was 100 per cent removal of oil from the membrane. We were able to get back all the oil used,” Mr. Mukherjee adds.

Published in The Hindu on October 2, 2016

Pune researchers use bagasse to produce anode-grade carbon for Li-ion batteries

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The team led by Prof. Satishchandra Ogale (left) of IISER was  able to produce anode-grade carbon within minutes by using a simple microwave oven.

Now, researchers from Pune’s National Chemical Laboratory (NCL) and Indian Institute of Science Education and Research (IISER) have used a simple, cost-effective, quick process to convert sugarcane bagasse, an agro waste, into anode-grade porous, conducting, activated carbon material for use in Lithium-ion batteries.

While making anode-grade carbon is currently very expensive and time consuming, the Pune researchers were able to produce high quality carbon within minutes by using a low power microwave system. The results of the study were published on July 5 in the journal Electrochimica Acta.

The quality of carbon used for electrodes depends on the choice of precursors and the process used for converting the precursors into carbon. Anode-grade carbon is generally produced through pyrolysis (where decomposition is brought about by high temperature processing) which involves heating the precursors in a reducing atmosphere using argon gas for a day or two at temperatures as high as 1000 degree C.

The process time and electrical energy to get anode-grade carbon is cut down drastically.“By using a simple kitchen microwave oven we achieved local heating and combustion to realise high quality factory-grade carbon materials within a few minutes,” says Prof. Satishchandra Ogale the corresponding author from the Centre for Energy Science at IISER, Pune and formerly Chief Scientist, NCL, Pune.

“The process time to get anode-grade carbon is cut down dramatically. The electrical energy input is also reduced substantially,” Prof. Ogale says. “The quality of carbon and battery performance using this carbon is quite good and competitive with carbon made through other complicated schemes and processes. We are able to get competitive value of energy density and power density using the carbon anode made in the lab.”

The performance in terms of stability has also been good for a large number of charging and discharging cycles, according to them.

The process

The initial carbonisation was carried out overnight at room temperature by mixing bagasse with concentrated sulphuric acid. “Except silica most of the inorganic impurities present in bagasse get dissolved by acid treatment,” says Anil Suryawanshi, one of the authors of the paper from NCL, Pune. This also helps in forming robust C=C backbone structure.

The solid product formed after acid treatment is washed thoroughly with distilled water to remove all traces of acid and oven dried at 70 degree C. The black colour powder or char is then mixed with potassium hydroxide to form slurry. The slurry is then heated in a microwave oven for a few minutes.

“The mixture achieves a burning temperature for a few minutes.  It is a high-temperature thermal shock or combustion,” says Prof. Ogale. Though the flame temperature is high, it is self-generated by the microwave and not through external heating; the power consumed by the microwave oven is just 700-900 watts.

“Graphitisation takes place due to local heating with microwave and potassium hydroxide reacts with carbon to form soluble phases which eventually form pores,” says Suryawanshi.  The process is repeated one more time after mixing with water to optimize porosity and conductivity. Porosity is important as lithium ions come though liquid electrolyte and must reach different parts of the carbon anode.  Optimum porosity is needed for accessibility of lithium ions.

The carbon that is produced is made into a paste by mixing with a binder and a small amount of highly conductive material like graphite and coated on a metal foil using a brush or spatula to produce an anode.

Published in The Hindu on September 22, 2016

Pune researchers close to making cheaper, more efficient fuel cells

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The novel HOF materials made by IISER and NCL researchers have a high proton conduction value even at low humidity. Avishek Karmakar (left) and Dr. Sujit Ghosh of IISER, Pune are coauthors of the paper.

Researchers from Pune’s Indian Institute of Science Education and Research (IISER) and National Chemical Laboratory (NCL) have come one step closer to making fuel cells that are cheaper and more efficient. Two novel porous and crystalline hydrogen-bonded organic frameworks (HOFs) that they synthesised could potentially be used as a proton exchange membrane in fuel cells.

Nafion, the currently used proton exchange membrane, has major drawbacks in terms of applicability at high temperature range or low humidity, high production costs and gas leakage issues.

The proton-conducting materials synthesised by the researchers address one critical issue — achieving a high proton conduction value even at ambient conditions (low humidity of around 60 per cent and moderate temperature). The proton conduction value is greater at higher humidity. The results were published recently in the journal Angewandte Chemie.

At high humidity (95 per cent) the proton conductivity is comparable to the best materials.“Among all known porous materials, this is the highest proton conduction value that has been reported at ambient conditions,” says Avishek Karmakar, a research scholar from IISER and the first author of the paper.

“Our materials have the potential to be used as a proton exchange membrane to improve the efficiency of fuel cells. The cost of fuel cells will become cheaper as it is easy to make the membrane,” says Dr. Sujit K. Ghosh, the corresponding author of the paper from IISER.

The HOFs are promising materials for gas separation and storage applications. However, they have not been used for fuel cell applications.

The team synthesised two organic compounds, and each compound has a proton donor site and a proton acceptor site. “The donor-acceptor complementarity is distributed throughout the hydrogen-bonded framework,” says Karmakar.

“The hydrogen bonding serves as a pathway for proton transfer from the donor site to the acceptor site. Water acts as a carrier and plays an important role. Proton transfer becomes easy when humidity is high,” says Dr. Ghosh. “At ambient conditions, the proton conductivity is much higher than other related materials. And at high humidity (95 per cent) the proton conductivity is comparable to the best materials.”

The compounds are made of salt-like ionic materials and improving on the water stability is a challenge.  “Using crystal engineering we improved the water stability by increasing the hydrophobic nature of the compounds for real time applications in fuel cell industries,” says Dr. Ghosh. Though one compound has higher hydrophobic characteristics than the other, proton conductivity was high in both the compounds even at low humidity.

Other applications

 Additionally, the HOF compounds have the potential to remove greenhouse gases such as carbon dioxide. “Although the compounds reported by us separate carbon dioxide from other gases like nitrogen, oxygen and hydrogen at low temperatures, we believe that such materials, if designed systemically, can be used in industries to remove greenhouse gases,” Dr. Ghosh says.

Published in The Hindu on September 18, 2016