Ancestral mitoviruses discovered in mycorrhizal fungi

Peer-Reviewed Publication

HOKKAIDO UNIVERSITY

 

IMAGE: ARBUSCULAR MYCORRHIZAL (AM) FUNGI IN THE GLOMEROMYCOTINA COLONIZE PLANT ROOTS (LEFT, MICROGRAPH) AND DELIVER WATER AND NUTRIENTS FROM SOIL (RIGHT). (TATSUHIRO EZAWA). view more 

CREDIT: TATSUHIRO EZAWA

A new group of mitochondrial viruses confined to the arbuscular mycorrhizal fungi Glomeromycotina may represent an ancestral lineage of mitoviruses.

Mitochondria are organelles in the cells of almost all eukaryotes — organisms with cells that have a nucleus. They were originally free-living bacteria capable of generating energy in the presence of oxygen; then engulfed by an ancestral eukaryotic cell where they became mitochondria, the site of cellular respiration and many important metabolic processes. In humans, dysfunctions of mitochondria are associated with aging and many diseases.

Bacteriophages are viruses that infect bacteria. As former bacteria, there are also viruses that infect mitochondria, known as mitoviruses, which evolved from bacteriophages. While mitoviruses have been found in fungi, plants, and invertebrates, they are not well studied.

Associate Professor Tatsuhiro Ezawa at Hokkaido University, Professor Luisa Lanfranco at University of Turin, and Dr. Massimo Turina at National Research Council of Italy (CNR) Torino led an international team to discover a new group of mitoviruses, called large duamitoviruses. Their findings were published in the journal mBio.

“In their current form, mitoviruses are RNA molecules within mitochondria that encode only the RNA-dependent RNA polymerase (RdRp) used for genome replication,” explains Ezawa. “They are hypothesized to affect the virulence of plant pathogens and plant resilience to abiotic stress. Most interestingly, mitoviruses are transmitted not only vertically to progeny via mitochondrial division but occasionally also horizontally between distant species.”

The team analyzed the RdRp enzyme from 10 new mitoviruses and sequences from previous research and public databases. This analysis revealed the existence of peculiar large duamitoviruses that are exclusive to the Glomeromycotina, a group of mycorrhizal fungi which are very widespread in nature and provide several benefits to the host plants. 

These large duamitoviruses possess two structurally distinct characteristics: they encode larger than average RdRp (~1,036 amino acids long) with a unique amino acid motif, and the UGA codon is rarer than in other mitoviruses. Furthermore, a phylogenetic analysis showed that the large duamitoviruses were evolutionarily distinct from other mitoviruses and likely represent an ancestral lineage.

“One of our most interesting discoveries is that the large duamitoviruses appear to be exclusive to glomeromycotina,” Lanfranco described. “We analysed the global distribution of all the mitovirus RdRp sequences included in our study, and we found that large duamitoviruses were globally distributed in ecological niches occupied by glomeromycotinian fungi. Although other fungi are found in these niches, all currently available large duamitoviral sequences could be only associated with glomeromycotinian fungi.”

The team hypothesizes that there is a transmission barrier that prevents the horizontal transfer of large duamitoviruses. Future work will focus on understanding these barriers, on confirming that large duamitoviruses represent an ancestral lineage of mitoviruses, as well as elucidating the functional significance of their exclusive presence in glomeromycotina.

Phylogenetic analysis of the RNA-dependent RNA polymerase enzyme sequence shows that large duamitoviruses are the most ancestral group of mitoviruses (Tatsuhiro Ezawa).

Large duamitoviruses consist of 23% of the glomeromycotinian mitoviruses (left) that are about one-third of the 5,343 mitoviruses detected in the soil samples collected worldwide. Sampling sites from which large duamitoviruses were detected are mapped (triangles, right). (Tatsuhiro Ezawa).

CREDIT

Tatsuhiro Ezawa

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JOURNAL

mBio

DOI

10.1128/mbio.00240-23 

METHOD OF RESEARCH

Experimental study

SUBJECT OF RESEARCH

Not applicable

ARTICLE TITLE

Structurally distinct mitoviruses: Are they an ancestral lineage of the Mitoviridae exclusive to arbuscular mycorrhizal fungi (Glomeromycotina)?

ARTICLE PUBLICATION DATE

10-May-2023

How bacteria evolve resistance to antibiotics

Peer-Reviewed Publication

UNIVERSITY OF EAST ANGLIA

How bacteria evolve resistance to antibiotics

Bacteria can rapidly evolve resistance to antibiotics by adapting special pumps to flush them out of their cells, according to new research from the Quadram Institute and University of East Anglia.

Antimicrobial resistance is a growing problem of global significance. The rise of resistant “superbugs” threatens our ability to use antimicrobials like antibiotics to treat and prevent the spread of infections caused by microorganisms.

It is hoped that the findings will improve how antibiotics are used to help prevent further spread of antimicrobial resistance.

Prof Mark Webber UEA’s Norwich Medical School, and the Quadram Institute, said: “Knowing the details of the mechanisms bacteria develop to become resistant is a key step to understanding antimicrobial resistance. We hope that this kind of work to understand when and how resistance emerges can help us use antibiotics better to minimise selection of resistance.”

The team studied how exposure to antimicrobials leads to the emergence of resistance.

Broadly, superbugs’ defences against antibiotics involve inactivating or evading drugs, stop them getting into their cells, or getting them out of their cells before they can have any effect. But exactly how they do this is still being worked out.

In this new study Dr Eleftheria Trampari from QI, Prof Webber, and colleagues recreated the evolutionary stresses that lead to antimicrobial resistance by exposing Salmonella bacteria to two different antibiotics.

The bacteria were allowed to grow and reproduce in two different states that mimic how they live in the environment.

Some were planktonic - floating in a liquid broth - but others were in biofilms. Bacteria form biofilms on surfaces, as a way of protecting themselves against stresses and most bacteria in the real world exist in a biofilm.

Hundreds of generations of bacteria were grown and exposed to the antibiotics, and in this evolution simulation, survival of the fittest selected those bacteria best adapted to cope with the presence of the antibiotics.

To identify how these ‘winners’ had become resistant, the researchers sequenced the genomes of the resistant bacteria, to identify which genes had changed compared to their non-resistant ancestors.

They found that both antibiotics selected different mutations in a molecular pump that Salmonella uses to get rid of toxic compounds from inside its cells. With colleagues from the University of Essex and University of Cagliari, they found that these two different changes altered how the pump worked in totally different ways. One made it easier for the pumps to catch drugs, the other made it easier for drugs to slide through the pump.

A search of a databases of genomes of Salmonella isolates found that one of these mutations has also arisen multiple times in the real world, in Salmonella from patients, livestock and food in the UK, US and EU, as far back as 2003.

The findings confirm a primary role for these pumps as the first line of defence against antimicrobials.

“This work simulates what happens in the real world where bacteria are constantly exposed to varying concentrations of antimicrobials” said Dr Eleftheria Trampari from the Quadram Institute and first author on the study. “Studying how resistant strains emerge and predict which drugs they will not respond to can be helpful in developing diagnostics and treatment strategies”.

The study was supported by the Biotechnology and Biological Sciences Research Council, part of UKRI.

‘Functionally distinct mutations within AcrB underpin antibiotic 2 resistance in different lifestyles’ is published in the journal Antimicrobials and Resistance.

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METHOD OF RESEARCH

Experimental study

ARTICLE TITLE

‘Functionally distinct mutations within AcrB underpin antibiotic 2 resistance in different lifestyles

ARTICLE PUBLICATION DATE

10-May-2023

Researchers track antimicrobial resistance in E. coli isolated from swine

Peer-Reviewed Publication

CARL R. WOESE INSTITUTE FOR GENOMIC BIOLOGY, UNIVERSITY OF ILLINOIS AT URBANA-CHAMPAIGN

 

IMAGE: HAMID REZA SODAGARI, LEFT, AND CSABA VARGA ARE WORKING ON TRACKING THE RISE OF ANTIMICROBIAL RESISTANCE IN BACTERIA THAT ARE COMMONLY ASSOCIATED WITH LIVESTOCK. view more 

CREDIT: CSABA VARGA

The spread of drug-resistant microbes has become a global health concern that threatens our ability to treat infections. The widespread use of antimicrobials in livestock, such as swine farms, exacerbates this problem. Therefore, we need surveillance systems to monitor these microbes to support the public health authorities. To this end, researchers have tracked the antimicrobial resistance of Escherichia coli isolated from swine.

Antimicrobials are essential for preventing and treating infections in humans and animals. According to the US Food and Drug Administration, 70% of all antibiotic sales in the US are used for livestock production. However, microbes change over time to combat these chemicals, eventually becoming resistant. As a result, infections become harder to treat. Concerningly, these resistant organisms can spread from farm animals to humans, creating a bigger health crisis.

The researchers focused on E. coli since these bacteria are ubiquitous in the intestinal tract of humans and pigs, and they are good indicators to test whether meat and meat products have been contaminated. E. coli can also acquire and transfer resistance genes to other bacteria in the intestinal tract, making them ideal for monitoring programs of livestock and humans.

“It is important to monitor the emergence of antimicrobial-resistant bacteria in the swine industry because in 2022 the US was the third largest producer and consumer of swine meat and products, after the European Union and China,” said Hamid Reza Sodagari, a postdoctoral research associate in the Varga lab. “Although it is a big problem, to the best of our knowledge this paper is the first surveillance study in the US that looks at antimicrobial resistance in E. coli from swine at slaughter.”

The study used publicly available surveillance data of cecal samples, which were collected from the intestine after slaughter. The researchers focused on market swine and sows in the US between 2013 and 2019, and used the data compiled by the United States Department of Agriculture Food Safety Inspection Service under the National Antimicrobial Resistance Monitoring System for Enteric Bacteria program.

“Federal agencies often don’t have the manpower to carry out such long-term and detailed analyses. Alternatively, for most researchers such studies are challenging because usually they track samples on a smaller scale. In this paper, however, we were able to look at more than 3,000 samples across several years,” said Csaba Varga (IGOH), an assistant professor of  epidemiology.

Using different statistical methods, the researchers found that since 2013, the number of antimicrobials to which E. coli is resistant has either remained steady or increased over the years. In particular, the resistance to ceftriaxone, an important antimicrobial drug in both human and veterinary medicine, increased from 0.8% in 2013 to 7.7% in 2019. Even though these numbers are not high compared to the resistance to other antimicrobials, the increasing trend is concerning.

“We don’t know why there is an increasing trend. It may be caused by mobile genetic elements, which can transfer antimicrobial resistance from one bacterium to another. We need to do further research at the molecular level to understand the reason for the increase,” Sodagari said.

“We are not blaming anyone for this problem. Our study is meant to show that there is an issue and that surveillance systems are very important to show the changes in resistance,” Varga said. “By gathering this data, we hope that the public health authorities will be able to develop mitigation strategies.”

The study “Evaluating Antimicrobial Resistance Trends in Commensal Escherichia coli Isolated from Cecal Samples of Swine at Slaughter in the United States, 2013-2019” was published in Microorganisms and can be found at 10.3390/microorganisms11041033.

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JOURNAL

Microorganisms

DOI

10.3390/microorganisms11041033 

METHOD OF RESEARCH

Data/statistical analysis

SUBJECT OF RESEARCH

Animals

ARTICLE TITLE

Evaluating Antimicrobial Resistance Trends in Commensal Escherichia coli Isolated from Cecal Samples of Swine at Slaughter in the United States, 2013–2019

Bacteria killing material could tackle hospital superbugs

Peer-Reviewed Publication

UNIVERSITY OF NOTTINGHAM

Researchers have used a common disinfectant and antiseptic to create a new antimicrobial coating material that effectively kills bacteria and viruses, including MRSA and Covid-19.

Scientists at the University of Nottingham’s School of Pharmacy took chlorhexidine, often used by dentists to treat mouth infections and for pre-surgical cleaning, and used it to coat the polymer, acrylonitrile butadiene styrene (ABS). The new study published in Nano Select shows that this new material was found to be effective in killing the microbes responsible for a range of infections and illnesses and could be used as an effective antimicrobial coating on a range of plastic products.

Plastics are widely used in medical settings, from intravenous bags and implantable devices to hospital beds and toilet seats. Some microbial species can survive in a hospital setting despite enhanced cleaning regimes, leading to an increased risk of patients getting infections whilst in hospital which then need antibiotic treatment. These microorganisms can survive and remain infectious on abiotic surfaces, including plastic surfaces, for extended periods, sometimes up to several months.

Dr Felicity de Cogan, Assistant Professor in Pharmaceutical Science of Biological Medicines led this study, she said: “As plastic is such a widely used material that we know can harbour infectious microorganisms we wanted to investigate a way to use this material to destroy the bacteria. We achieved this by bonding a disinfectant with the polymer to create a new coating material and discovered not only does it act very quickly, killing bacteria within 30 minutes, it also doesn’t spread into the environment or leach from the surface when touched. Making plastic items using this material could really help tackle the issue of antibiotic resistance and reduce hospital acquired infections.”

The researchers used a special imaging technique called Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) to examine the material at molecular level. This revealed the material was antimicrobial and rapidly killed microbes and after 45 minutes the surfaces were still clear of these microbes. It was also effective against SARS-COV-2, with no viable virions found after 30 minutes. Additionally, the surfaces were also effective in killing chlorhexidine-resistant strains of bacteria.

The COVID-19 pandemic has drawn increased attention to hospital-acquired infections, as it has been estimated that 20% of all patients hospitalized with COVID-19 contracted the virus while already in hospital. It has been estimated that in 2016/17, 4.7% of adult hospital inpatients contracted an infection whilst in hospital, with 22,800 patients dying due to these infections despite these deaths being preventable. The most common pathogens that cause hospital-acquired infections are Escherichia coli, Staphylococcus aureus, and Clostridium difficile. Outbreaks of infection in the clinic are frequently caused by strains resistant to antimicrobial drugs.

Dr de Cogan continues: “Research has shown that contaminated surfaces, including plastic surfaces, can act as a reservoir of antimicrobial resistance genes, encouraging the spread of antimicrobial resistance across bacterial species through horizontal gene transfer despite deep cleaning practices. It is paramount that new technologies are developed to prevent the spread of pathogenic microorganisms to vulnerable patients and address the ever-increasing threat of antimicrobial resistance.

“This research offers an effective way to do this and the material could be added to plastic materials during manufacture, it could also potentially be used as a spray.”

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JOURNAL

Nano Select

DOI

10.1002/nano.202300005 

METHOD OF RESEARCH

Experimental study

SUBJECT OF RESEARCH

Not applicable

ARTICLE TITLE

Development of biocide coated polymers and their antimicrobial efficacy

ARTICLE PUBLICATION DATE

10-May-2023

Bacteria: Radioactive elements replace 

essential rare earth metals

Peer-Reviewed Publication

LUDWIG-MAXIMILIANS-UNIVERSITÄT MÜNCHEN

A team led by LMU chemist Lena Daumann has demonstrated for the first time that bacteria can use certain radioactive elements to sustain their metabolism.

As well as being a useful material in all kinds of key technologies, lanthanides are important for bacteria, which use the rare earth metals in their metabolism. It turns out, however, that they are not as irreplaceable as previously thought, as an international and interdisciplinary team led by Professor Lena Daumann from the Department of Chemistry at LMU has demonstrated: Certain bacteria can use the radioactive elements americium and curium instead of the lanthanides – and even prefer them sometimes.

Bacteria that use lanthanides are widespread in the environment. They belong to the so-called methylotrophs, which can use methanol or methane as carbon and energy sources. To do this, they take up lanthanides and incorporate them into an important metabolic enzyme, a lanthanide-dependent methanol dehydrogenase. The elements americium and curium, members of the radioactive actinides, are very similar to the lanthanides when it comes to key chemical properties such as size and charge. “And so we asked ourselves whether the bacteria can use actinides instead of their essential lanthanides,” says Daumann.

Now the researchers have demonstrated that this is actually the case. They carried out an in-vivo study of two methylotrophic bacterial strains in collaboration with the Helmholtz Center in Dresden-Rossendorf (HZDR). “We fed the microbes various elements and showed that they incorporate americium and curium and grow just as well with these elements,” explains Daumann. It is important that the actinides have the same oxidation state and are of a similar size to the lanthanides normally used, so that they fit in the  active center of methanol dehydrogenase. Additional in-vitro studies with isolated methanol dehydrogenase also demonstrate that the enzyme works with the actinides and exhibits similar activities.

“We could thus show for the first time that organisms can use these radioactive elements for life processes,” emphasizes Daumann. When the bacteria were offered a mixture of various lanthanides and actinides, they even preferred americium and curium ahead of some lanthanides. The ability of the bacteria to incorporate radioactive actinides is also interesting with respect to potential applications: “Methylotrophic bacteria could potentially be used in bioremediation or in the separation and recycling of lanthanides and actinides. Such difficult-to-separate mixtures are often found in spent nuclear fuel,” says Daumann.

JOURNAL

Angewandte Chemie

DOI

10.1002/anie.202303669 

ARTICLE TITLE

Minor Actinides Can Replace Essential Lanthanides in Bacterial Life

Bacteria survive on radioactive

elements

Bacteria can replace lanthanides with actinides to sustain their metabolism

Peer-Reviewed Publication

WILEY

Bacteria that feed on methanol are able to grow on certain rare earth elements as well as their radioactive relatives. These findings suggest a possible role for such bacteria in the decontamination of areas where actinides are spilled, or in the separation of lanthanides and actinides for analytical or preparative purposes, according to a study published in the journal Angewandte Chemie.

Lanthanides belong to the rare earth elements widely used in electronics and energy technologies. With one exception, they are not radioactive, they are abundant in the earth's crust, and some lanthanides such as lanthanum and neodymium even play a crucial role in bacterial metabolism. Actinides, which include uranium and plutonium, are their heavy, radioactive counterparts, most of which are not found naturally on earth. Now, Lena Daumann from Ludwig-Maximilians-University Munich, Germany, and her international interdisciplinary team have discovered that some actinides can replace essential lanthanides in the metabolism of methylotrophic bacteria.

Methylotrophic bacteria, so-called as they use methanol as their energy source, contain lanthanides in their methanol-oxidizing enzyme. The researchers observed that these bacteria could also take up actinide ions into this enzyme, using them for methanol metabolism in the same way as they would use lanthanides. This observation was particularly valid when the actinide ions were the same size and had the same stable +III oxidation states as the corresponding lanthanides. The bacteria even preferred americium and curium as actinides over some lanthanides when presented with a mixture of lanthanides and actinides, the researchers reported.

Americium and curium showed a stable +III oxidation state, which appeared to be particularly important. “When we used plutonium, which is known to have higher oxidation states, our bacteria did not grow, nor did the isolated enzymes work with it either,” Daumann says. This knowledge will be useful for future applications. The team plans to explore the ability of the bacteria to extract actinides from radioactive waste or to separate out specific elements from mixtures.

Actinides such as plutonium, americium, and curium can be generated in nuclear reactors and are used in research, the nuclear industry, and many other technologies. Americium is even a source of ionizing radiation in commercial smoke detectors. However, actinides are highly radioactive and hazardous elements, which have to be handled with great care at special facilities. Spillages of radioactive substances are always of great concern. Dauman proposes “putting these bacteria to use to help clean up radioactive spills,” as a possible future application.

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About the Author

Lena Daumann is a Professor at the Chemistry Department at Ludwig-Maximilians-Universität München, Munich, Germany. Using model complexes, kinetic studies, and spectroscopic techniques, her interdisciplinary research group elucidates the mechanisms of action of lanthanides in lanthanide-dependent bacteria and enzymes.

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JOURNAL

Angewandte Chemie International Edition

DOI

10.1002/anie.202303669 

METHOD OF RESEARCH

Experimental study

SUBJECT OF RESEARCH

Cells

ARTICLE TITLE

Minor Actinides Can Replace Essential Lanthanides in Bacterial Life

Saving desalination membranes from minerals and microbes

Peer-Reviewed Publication

KING ABDULLAH UNIVERSITY OF SCIENCE & TECHNOLOGY (KAUST)

 

IMAGE: FROM LEFT: KAUST RESEARCH SCIENTIST GRACIELA GONZALEZ GIL, ACWA POWER’S RATUL DAS AND KAUST ALUMNA GHADEER HASANIN DISCUSS THEIR RESULTS. view more 

CREDIT: © 2023 KAUST; ELIZA MKHITARYAN.

Identifying the components of membrane antiscalants that cause biofouling could help make seawater desalination a more sustainable source of fresh water.

“Safe drinking water is a human right,” says environmental scientist Graciela Gonzalez-Gil, “yet roughly 800 million people have no access.” The United Nations estimates that demand for fresh water could exceed the natural water cycle supply by as much as 40 percent by 2030.

“Seawater desalination — particularly by reverse osmosis (SWRO), which involves pressurizing seawater through a membrane at high pressure to remove salt and impurities — has become a widely adopted low-cost source of drinking water in arid coastal countries,” says Gonzalez-Gil’s colleague and KAUST alumni Ratul Das, who now works as Head of Desalination R&D for energy company ACWA Power, which has 16 water seawater desalination plants across four countries.

However, SWRO is energy intensive, and the used membranes create a lot of waste. Seawater is typically pretreated with antiscalants to prevent the scaling of salt on the membranes. “The low cost of these chemicals compared to other methods helps keep water prices low, hence their popularity,” says Das. But many of them trigger fouling by promoting microbial growth.

“Desalination operators are not fully informed about why and to what extent antiscalants cause biofouling,” says Gonzalez-Gil. “Measuring the bacterial growth caused by different antiscalants and linking this to their chemical composition can help these operators select products with minimal biofouling.”

Gonzalez-Gil’s team prepared vials of natural seawater with a small starting concentration of indigenous bacteria. Adding one of eight common antiscalants to separate vials, they measured daily bacterial growth and compared this to bacterial growth in seawater without antiscalant.

“We measured the carbon, phosphorous and nitrogen content of each antiscalant and used nuclear magnetic resonance to get a more detailed chemical fingerprint,” says Gonzalez-Gil.

The team found that some antiscalants contained other compounds besides the active ingredients[1]. One particular contaminant – orthophosphate – clearly promoted bacterial growth. “Surprisingly, not all phosphanate-based antiscalants were contaminated with orthophosphates,” says Gonzalez-Gil, “such as HEDP (1-hydroxyethylidene-(1,1-diphosphonic acid), which was also the only antiscalant that didn’t promote bacterial growth.”

The team’s chemical fingerprinting technique could help manufacturers tailor antiscalants to contain fewer bacteria-boosting compounds. “Reducing biofouling will reduce the energy required for SWRO,” says Das. “It will lower the costs of desalination and, by reducing greenhouse emissions, will help to protect the planet.”

Reverse osmosis membranes are currently replaced every three to five years, despite a potential lifespan of 10 to 15 years. “Minimizing biofouling will extend their useful life and reduce the membrane waste deposited to landfill,” adds Gonzales-Gil.

Das hopes to develop a simple low-tech test for use at desalination plants worldwide. “We want to eliminate ‘black boxes’ in the desalination industry and drive greener initiatives that have impact for Saudi Arabia and internationally,” he adds.

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JOURNAL

Water Research

DOI

10.1016/j.watres.2023.119802 

ARTICLE TITLE

The microbial growth potential of antiscalants used in seawater desalination

Metal-filtering sponge removes lead from water

Reusable sponge can capture and recover critical metals and heavy-metal pollutants

Peer-Reviewed Publication

NORTHWESTERN UNIVERSITY

 

IMAGE: COMMERCIALLY AVAILABLE CELLULOSE SPONGE COATED IN MANGANESE-DOPED GOETHITE NANOPARTICLES view more 

CREDIT: CAROLINE HARMS/NORTHWESTERN UNIVERSITY

Northwestern University engineers have developed a new sponge that can remove metals — including toxic heavy metals like lead and critical metals like cobalt — from contaminated water, leaving safe, drinkable water behind.

In proof-of-concept experiments, the researchers tested their new sponge on a highly contaminated sample of tap water, containing more than 1 part per million of lead. With one use, the sponge filtered lead to below detectable levels.

After using the sponge, researchers also were able to successfully recover metals and reuse the sponge for multiple cycles. The new sponge shows promise for future use as an inexpensive, easy-to-use tool in home water filters or large-scale environmental remediation efforts.

The study was published late yesterday (May 10) in the journal ACS ES&T Water. The paper outlines the new research and sets design rules for optimizing similar platforms for removing — and recovering — other heavy-metal toxins, including cadmium, arsenic, cobalt and chromium.

“The presence of heavy metals in the water supply is an enormous public health challenge for the entire globe,” said Northwestern’s Vinayak Dravid, senior author of the study. “It is a gigaton problem that requires solutions that can be deployed easily, effectively and inexpensively. That’s where our sponge comes in. It can remove the pollution and then be used again and again.”

Dravid is the Abraham Harris Professor of Materials Science and Engineering at Northwestern’s McCormick School of Engineering and director of global initiatives at the International Institute for Nanotechnology.

Sopping up spills

The project builds on Dravid’s previous work to develop highly porous sponges for various aspects of environmental remediation. In May 2020, his team unveiled a new sponge designed to clean up oil spills. The nanoparticle-coated sponge, which is now being commercialized by Northwestern spinoff MFNS Tech, offers a more efficient, economic, ecofriendly and reusable alternative to current approaches to oil spills.

But Dravid knew it wasn’t enough.

“When there is an oil spill, you can remove the oil,” he said. “But there also are toxic heavy metals — like mercury, cadmium, sulfur and lead — in those spills. So, even when you remove the oil, some of the other toxins might remain.

Rinse and repeat

To tackle this aspect of the issue, Dravid’s team, again, turned to sponges coated with an ultrathin layer of nanoparticles. After testing many different types of nanoparticles, the team found that a manganese-doped goethite coating worked best. Not only are manganese-doped goethite nanoparticles inexpensive to make, easily available and nontoxic to human, they also have the properties necessary to selectively remediate heavy metals.

“You want a material with a high surface area, so there’s more room for the lead ions to stick to it,” said Benjamin Shindel, a Ph.D. student in Dravid’s lab and the paper’s first author. “These nanoparticles have high-surface areas and abundant reactive surface sites for adsorption and are stable, so they can be reused many times.”

The team synthesized slurries of manganese-doped goethite nanoparticles, as well as several other compositions of nanoparticles, and coated commercially available cellulose sponges with these slurries. Then, they rinsed the coated sponges with water in order to wash away any loose particles. The final coatings measured just tens of nanometers in thickness.

When submerged into contaminated water, the nanoparticle-coated sponge effectively sequested lead ions. The U.S. Food and Drug Administration requires that bottled drinking water is below 5 parts per billion of lead. In filtration trials, the sponge lowered the amount of lead to approximately 2 parts per billion, making it safe to drink.

“We’re really happy with that,” Shindel said. “Of course, this performance can vary based on several factors. For instance, if you have a large sponge in a tiny volume of water, it will perform better than a tiny sponge in a huge lake.”

Recovery bypasses mining

From there, the team rinsed the sponge with mildly acidified water, which Shindel likened to “having the same acidity of lemonade.” The acidic solution caused the sponge to release the lead ions and be ready for another use. Although the sponge’s performance declined after the first use, it still recovered more than 90% of the ions during subsequent use cycles.

This ability to gather and then recover heavy metals is particularly valuable for removing rare, critical metals, such as cobalt, from water sources. A common ingredient in lithium-ion batteries, cobalt is energetically expensive to mine and accompanied by a laundry list of environmental and human costs.

If researchers could develop a sponge that selectively removes rare metals, including cobalt, from water, then those metals could be recycled into products like batteries.

“For renewable energy technologies, like batteries and fuel cells, there is a need for metal recovery,” Dravid said. “Otherwise, there is not enough cobalt in the world for the growing number of batteries. We must find ways to recover metals from very dilute solutions. Otherwise, it becomes poisonous and toxic, just sitting there in the water. We might as well make something valuable with it.”

Commercially available cellulose sponges coated with nanoparticles

CREDIT

Caroline Harms/Northwestern University

Standardized scale

As a part of the study, Dravid and his team set new design rules to help others develop tools to target particular metals, including cobalt. Specifically, they pinpointed which low-cost and nontoxic nanoparticles also have high-surface areas and affinities for sticking to metal ions. They studied the performance of coatings of manganese, iron, aluminum and zinc oxides on lead adsorption. Then, they established relationships between the structures of these nanoparticles and their adsorptive properties.

Called Nanomaterial Sponge Coatings for Heavy Metals (or “Nano-SCHeMe”), the environmental remediation platform can help other researchers differentiate which nanomaterials are best suited for particular applications.

“I’ve read a lot of literature that compares different coatings and adsorbents,” said Caroline Harms, an undergraduate student in Dravid’s lab and paper co-author. “There really is a lack of standardization in the field. By analyzing different types of nanoparticles, we developed a comparative scale that actually works for all of them. It could have a lot of implications in moving the field forward.”

Dravid and his team imagine that their sponge could be used in commercial water filters, for environmental clean-up or as an added step in water reclamation and treatment facilities.

“This work may be pertinent to water quality issues both locally and globally,” Shindel said. “We want to see this out in the world, where it can make a real impact.”

The study, “Nano-SCHeME: Nanomaterial Sponge Coatings for Heavy Metals, an environmental remediation platform,” was supported by the National Science Foundation and U.S. Department of Energy.

Editor’s note: Dravid and Northwestern have financial interests (equities, royalties) in MFNS Tech.

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JOURNAL

ACS ES&T Water

DOI

10.1021/acsestwater.2c00646 

METHOD OF RESEARCH

Experimental study

SUBJECT OF RESEARCH

Not applicable

ARTICLE TITLE

Nano-SCHeMe: Nanomaterial Sponge Coatings for Heavy Metals, an Environmental Remediation Platform