Maize and bacteria: A 1-2 punch knocks copper out of stamp sand

Maize plants grown in stamp sand inoculated with bacteria, left, were considerably more robust than those grown in stamp sand alone, right. Research led by Michigan Technological University's Ramakrishna Wusirika could lead to new remediation techniques for soils contaminated by copper and other heavy metals. -  Ramakrishna Wusirika
Maize plants grown in stamp sand inoculated with bacteria, left, were considerably more robust than those grown in stamp sand alone, right. Research led by Michigan Technological University’s Ramakrishna Wusirika could lead to new remediation techniques for soils contaminated by copper and other heavy metals. – Ramakrishna Wusirika

Scientists have known for years that together, bacteria and plants can remediate contaminated sites. Ramakrishna Wusirika, of Michigan Technological University, has determined that how you add bacteria to the mix can make a big difference.

He has also shed light on the biochemical pathways that allow plants and bacteria to clean up some of the worst soils on the planet while increasing their fertility.

Wusirika, an associate professor of biological sciences, first collected stamp sands near the village of Gay, in Michigan’s Upper Peninsula. For decades, copper mining companies crushed copper ore and dumped the remnants-an estimated 500 million tons of stamp sand-throughout the region. Almost nothing grows on these manmade deserts, which are laced with high concentrations of copper, arsenic and other plant-unfriendly chemicals.

Then, Wusirika and his team planted maize in the stamp sand, incorporating bacteria in four different ways:

  • mixing it in the stamp sand before planting seed;

  • coating seed with bacteria and planting it;

  • germinating seeds and planting them in soil to which bacteria were added; and

  • the conventional method, immersing the roots of maize seedlings in bacteria and planting them in stamp sand.

After 45 days, the team uprooted the plants and measured their dry weight. All maize grown with bacteria was significantly more vigorous-from two to five times larger-than the maize grown in stamp sand alone. The biggest were those planted as seedlings or as germinated seeds.

However, when the researchers analyzed the dried maize, they made a surprising discovery: the seed-planted maize took up far more copper as a percentage of dry weight. In other words, the smaller plants pulled more copper, ounce per ounce, out of the stamp sands than the bigger ones.

That has implications for land managers trying to remediate contaminated sites, or even for farmers working with marginal soils, Wusirika said. The usual technique-applying bacteria to seedlings’ roots before transplanting-works fine in the lab but would be impractical for large-scale projects. This could open the door to simple, practical remediation of copper-contaminated soils.

But the mere fact that all the plants grown with bacteria did so well also piqued his curiosity. “When we saw this, we wondered what the bacteria were doing to the soil,” Wusirika said. “Based on our research, it looks like they are improving enzyme activity and increasing soil fertility,” in part by freeing up phosphorus that had been locked in the rock.

The bacteria are also changing copper into a form that the plants can take up. “With bacteria, the exchangeable copper is increased three times,” he said. “There’s still a lot of copper that’s not available, but it is moving in the right direction.”

By analyzing metabolic compounds, the team was able to show that the bacteria enhance photosynthesis and help the plants make growth hormones. Bacteria also appear to affect the amount phenolics produced by the maize. Phenolics are antioxidants similar to those in grapes and red wine.

Compared to plants grown in normal soil without bacteria, plants grown in stamp sand alone showed a five-fold increase in phenolics. However, phenolics in plants grown in stamp sand with bacteria showed a lesser increase.

“Growing in stamp sand is very stressful for plants, and they respond by increasing their antioxidant production,” Wusirika said. “Adding the metal-resistant bacteria enables the plants to cope with stress better, resulting in reduced levels of phenolics.”

“There’s still a lot to understand here,” he added. “We’d like to do a study on stamp sands in the field, and we’d also like to work with plants besides maize. We think this work has applications in organic agriculture as well as remediation.”

Maize and bacteria: A 1-2 punch knocks copper out of stamp sand

Maize plants grown in stamp sand inoculated with bacteria, left, were considerably more robust than those grown in stamp sand alone, right. Research led by Michigan Technological University's Ramakrishna Wusirika could lead to new remediation techniques for soils contaminated by copper and other heavy metals. -  Ramakrishna Wusirika
Maize plants grown in stamp sand inoculated with bacteria, left, were considerably more robust than those grown in stamp sand alone, right. Research led by Michigan Technological University’s Ramakrishna Wusirika could lead to new remediation techniques for soils contaminated by copper and other heavy metals. – Ramakrishna Wusirika

Scientists have known for years that together, bacteria and plants can remediate contaminated sites. Ramakrishna Wusirika, of Michigan Technological University, has determined that how you add bacteria to the mix can make a big difference.

He has also shed light on the biochemical pathways that allow plants and bacteria to clean up some of the worst soils on the planet while increasing their fertility.

Wusirika, an associate professor of biological sciences, first collected stamp sands near the village of Gay, in Michigan’s Upper Peninsula. For decades, copper mining companies crushed copper ore and dumped the remnants-an estimated 500 million tons of stamp sand-throughout the region. Almost nothing grows on these manmade deserts, which are laced with high concentrations of copper, arsenic and other plant-unfriendly chemicals.

Then, Wusirika and his team planted maize in the stamp sand, incorporating bacteria in four different ways:

  • mixing it in the stamp sand before planting seed;

  • coating seed with bacteria and planting it;

  • germinating seeds and planting them in soil to which bacteria were added; and

  • the conventional method, immersing the roots of maize seedlings in bacteria and planting them in stamp sand.

After 45 days, the team uprooted the plants and measured their dry weight. All maize grown with bacteria was significantly more vigorous-from two to five times larger-than the maize grown in stamp sand alone. The biggest were those planted as seedlings or as germinated seeds.

However, when the researchers analyzed the dried maize, they made a surprising discovery: the seed-planted maize took up far more copper as a percentage of dry weight. In other words, the smaller plants pulled more copper, ounce per ounce, out of the stamp sands than the bigger ones.

That has implications for land managers trying to remediate contaminated sites, or even for farmers working with marginal soils, Wusirika said. The usual technique-applying bacteria to seedlings’ roots before transplanting-works fine in the lab but would be impractical for large-scale projects. This could open the door to simple, practical remediation of copper-contaminated soils.

But the mere fact that all the plants grown with bacteria did so well also piqued his curiosity. “When we saw this, we wondered what the bacteria were doing to the soil,” Wusirika said. “Based on our research, it looks like they are improving enzyme activity and increasing soil fertility,” in part by freeing up phosphorus that had been locked in the rock.

The bacteria are also changing copper into a form that the plants can take up. “With bacteria, the exchangeable copper is increased three times,” he said. “There’s still a lot of copper that’s not available, but it is moving in the right direction.”

By analyzing metabolic compounds, the team was able to show that the bacteria enhance photosynthesis and help the plants make growth hormones. Bacteria also appear to affect the amount phenolics produced by the maize. Phenolics are antioxidants similar to those in grapes and red wine.

Compared to plants grown in normal soil without bacteria, plants grown in stamp sand alone showed a five-fold increase in phenolics. However, phenolics in plants grown in stamp sand with bacteria showed a lesser increase.

“Growing in stamp sand is very stressful for plants, and they respond by increasing their antioxidant production,” Wusirika said. “Adding the metal-resistant bacteria enables the plants to cope with stress better, resulting in reduced levels of phenolics.”

“There’s still a lot to understand here,” he added. “We’d like to do a study on stamp sands in the field, and we’d also like to work with plants besides maize. We think this work has applications in organic agriculture as well as remediation.”

First-ever 3D image created of the structure beneath Sierra Negra volcano

This is a photo of the Sierra Negra volcano on Isabela Island in the Galápagos Archipelago. -  Cynthia Ebinger, University of Rochester
This is a photo of the Sierra Negra volcano on Isabela Island in the Galápagos Archipelago. – Cynthia Ebinger, University of Rochester

The Galápagos Islands are home to some of the most active volcanoes in the world, with more than 50 eruptions in the last 200 years. Yet until recently, scientists knew far more about the history of finches, tortoises, and iguanas than of the volcanoes on which these unusual fauna had evolved.

Now research out of the University of Rochester is providing a better picture of the subterranean plumbing system that feeds the Galápagos volcanoes, as well as a major difference with another Pacific Island chain-the Hawaiian Islands. The findings have been published in the Journal of Geophysical Research: Solid Earth.

“With a better understanding of what’s beneath the volcanoes, we’ll now be able to more accurately measure underground activity,” said Cynthia Ebinger, a professor of earth and environmental sciences. “That should help us better anticipate earthquakes and eruptions, and mitigate the hazards associated with them.”

Ebinger’s team, which included Mario Ruiz from the Instituto Geofisico Escuela Politecnica Nacional in Quito, Ecuador, buried 15 seismometers around Sierra Negra, the largest and most active volcano in the Galápagos. The equipment was used to measure the velocity and direction of different sound waves generated by earthquakes as they traveled under Sierra Negra. Since the behavior of the waves varies according to the temperature and types of material they’re passing through, the data collected allowed the researchers to construct a 3D image of the plumbing system beneath the volcano, using a technique similar to a CAT-scan.

Five kilometers down is the beginning of a large magma chamber lying partially within old oceanic crust that had been buried by more than 8 km of eruptive rock layers. And the oceanic crust has what appears to be a thick underplating of rock formed when magma that was working its way toward the surface became trapped under the crust and cooled-very much like the processes that occur under the Hawaiian Islands.

The researchers found that the Galápagos had something else in common with the Hawaiian Islands. Their data suggest the presence of a large chamber filled with crystal-mush magma-cooled magma that includes crystallized minerals.

The Galápagos Islands formed from a hotspot of magma located in an oceanic plate-called Nazca-about 600 miles of Ecuador, in a process very similar to how the Hawaiian Islands were created. Magma rising from the hotspot eventually hardened into an island. Then, as the Nazca plate inched its way westward, new islands formed in the same manner, resulting in the present-day Galápagos Archipelago.

While there are several similarities between the two island chains, Ebinger uncovered a major difference. The older volcanos in the Hawaiian Islands are dormant, because they’ve moved away from the hotspot that provided the source of magma. In the Galápagos, the volcanoes are connected to the same plumbing system. By studying satellite views of the volcanoes, Ebinger and colleagues noticed that, as the magma would sink in one, it would rise in a different volcano-indicating that that some of the youngest volcanoes had magma connections, even if those connections were temporary.

“Not only do we have a better understanding of the physical properties of Sierra Negra,” said Ebinger, “we have increased out knowledge of island volcano systems, in general.”

The Galápagos Islands are home to some of the most active volcanoes in the world, with more than 50 eruptions in the last 200 years. Yet until recently, scientists knew far more about the history of finches, tortoises, and iguanas than of the volcanoes on which these unusual fauna had evolved.

Now research out of the University of Rochester is providing a better picture of the subterranean plumbing system that feeds the Galápagos volcanoes, as well as a major difference with another Pacific Island chain-the Hawaiian Islands.

First-ever 3D image created of the structure beneath Sierra Negra volcano

This is a photo of the Sierra Negra volcano on Isabela Island in the Galápagos Archipelago. -  Cynthia Ebinger, University of Rochester
This is a photo of the Sierra Negra volcano on Isabela Island in the Galápagos Archipelago. – Cynthia Ebinger, University of Rochester

The Galápagos Islands are home to some of the most active volcanoes in the world, with more than 50 eruptions in the last 200 years. Yet until recently, scientists knew far more about the history of finches, tortoises, and iguanas than of the volcanoes on which these unusual fauna had evolved.

Now research out of the University of Rochester is providing a better picture of the subterranean plumbing system that feeds the Galápagos volcanoes, as well as a major difference with another Pacific Island chain-the Hawaiian Islands. The findings have been published in the Journal of Geophysical Research: Solid Earth.

“With a better understanding of what’s beneath the volcanoes, we’ll now be able to more accurately measure underground activity,” said Cynthia Ebinger, a professor of earth and environmental sciences. “That should help us better anticipate earthquakes and eruptions, and mitigate the hazards associated with them.”

Ebinger’s team, which included Mario Ruiz from the Instituto Geofisico Escuela Politecnica Nacional in Quito, Ecuador, buried 15 seismometers around Sierra Negra, the largest and most active volcano in the Galápagos. The equipment was used to measure the velocity and direction of different sound waves generated by earthquakes as they traveled under Sierra Negra. Since the behavior of the waves varies according to the temperature and types of material they’re passing through, the data collected allowed the researchers to construct a 3D image of the plumbing system beneath the volcano, using a technique similar to a CAT-scan.

Five kilometers down is the beginning of a large magma chamber lying partially within old oceanic crust that had been buried by more than 8 km of eruptive rock layers. And the oceanic crust has what appears to be a thick underplating of rock formed when magma that was working its way toward the surface became trapped under the crust and cooled-very much like the processes that occur under the Hawaiian Islands.

The researchers found that the Galápagos had something else in common with the Hawaiian Islands. Their data suggest the presence of a large chamber filled with crystal-mush magma-cooled magma that includes crystallized minerals.

The Galápagos Islands formed from a hotspot of magma located in an oceanic plate-called Nazca-about 600 miles of Ecuador, in a process very similar to how the Hawaiian Islands were created. Magma rising from the hotspot eventually hardened into an island. Then, as the Nazca plate inched its way westward, new islands formed in the same manner, resulting in the present-day Galápagos Archipelago.

While there are several similarities between the two island chains, Ebinger uncovered a major difference. The older volcanos in the Hawaiian Islands are dormant, because they’ve moved away from the hotspot that provided the source of magma. In the Galápagos, the volcanoes are connected to the same plumbing system. By studying satellite views of the volcanoes, Ebinger and colleagues noticed that, as the magma would sink in one, it would rise in a different volcano-indicating that that some of the youngest volcanoes had magma connections, even if those connections were temporary.

“Not only do we have a better understanding of the physical properties of Sierra Negra,” said Ebinger, “we have increased out knowledge of island volcano systems, in general.”

The Galápagos Islands are home to some of the most active volcanoes in the world, with more than 50 eruptions in the last 200 years. Yet until recently, scientists knew far more about the history of finches, tortoises, and iguanas than of the volcanoes on which these unusual fauna had evolved.

Now research out of the University of Rochester is providing a better picture of the subterranean plumbing system that feeds the Galápagos volcanoes, as well as a major difference with another Pacific Island chain-the Hawaiian Islands.

New study reveals insights on plate tectonics, the forces behind earthquakes, volcanoes

The Earth's outer layer is broken into moving, interacting plates whose motion at the surface generates most earthquakes, creates volcanoes and builds mountains. In this image, the orange layer represents the deformable, warm asthenosphere in which there is active mantle flow. The green layer is the lithospheric plate, which forms at the mid ocean ridge, then cools down and thickness as it moves away from the ridge. The cooling of the plate overprints a compositional boundary that forms at the ridge by dehydration melting and is preserved as the plate ages. The more easily deformable, hydrated rocks align with mantle flow. The directions of past and present-day mantle flow can be detected by seismic waves, and changes in the alignment of the rocks inside and at the bottom of the plate can be used to identify layering. -  Nicholas Schmerr/University of Maryland
The Earth’s outer layer is broken into moving, interacting plates whose motion at the surface generates most earthquakes, creates volcanoes and builds mountains. In this image, the orange layer represents the deformable, warm asthenosphere in which there is active mantle flow. The green layer is the lithospheric plate, which forms at the mid ocean ridge, then cools down and thickness as it moves away from the ridge. The cooling of the plate overprints a compositional boundary that forms at the ridge by dehydration melting and is preserved as the plate ages. The more easily deformable, hydrated rocks align with mantle flow. The directions of past and present-day mantle flow can be detected by seismic waves, and changes in the alignment of the rocks inside and at the bottom of the plate can be used to identify layering. – Nicholas Schmerr/University of Maryland

The Earth’s outer layer is made up of a series of moving, interacting plates whose motion at the surface generates earthquakes, creates volcanoes and builds mountains. Geoscientists have long sought to understand the plates’ fundamental properties and the mechanisms that cause them to move and drift, and the questions have become the subjects of lively debate.

A study published online Feb. 27 by the journal Science is a significant step toward answering those questions.

Researchers led by Caroline Beghein, assistant professor of earth, planetary and space sciences in UCLA’s College of Letters and Science, used a technique called seismic tomography to study the structure of the Pacific Plate – one of eight to 12 major plates at the surface of the Earth. The technique enabled them to determine the plate’s thickness, and to image the interior of the plate and the underlying mantle (the layer between the Earth’s crust and outer core), which they were able to relate to the direction of flow of rocks in the mantle.

“Rocks deform and flow slowly inside the Earth’s mantle, which makes the plates move at the surface,” said Beghein, the paper’s lead author. “Our research enables us to image the interior of the plate and helps us figure out how it formed and evolved.” The findings might apply to other oceanic plates as well.

Even with the new findings, Beghein said, the fundamental properties of plates “are still somewhat enigmatic.”

Seismic tomography is similar to commonly used medical imaging techniques like computed tomography, or CT, scans. But instead of using X-rays, seismic tomography employs recordings of the seismic waves generated by earthquakes, allowing scientists to detect variations in the speed of seismic waves inside the Earth. Those variations can reveal different layers within the mantle, and can help scientists determine the temperature and chemistry of the mantle rocks by comparing observed variations in wave speed with predictions from other types of geophysical data.

Seismologists often use other types of seismic data to identify this layering: They detect seismic waves that bounce off the interface that separates two layers. In their study, Beghein and co-authors compared the layering they observed using seismic tomography with the layers revealed by these other types of data. Comparing results from the different methods is a continuing challenge for geoscientists, but it is an important part of helping them understand the Earth’s structure.

“We overcame this challenge by trying to push the observational science to the highest resolutions, allowing us to more readily compare observations across datasets,” said Nicholas Schmerr, the study’s co-author and an assistant research scientist in geology at the University of Maryland.

The researchers were the first to discover that the Pacific Plate is formed by a combination of mechanisms: The plate thickens as the rocks of the mantle cool, the chemical makeup of the rocks that form the plate changes with depth, and the mechanical behavior of the rocks change with depth and their proximity to where the plate is being formed at the mid-ocean ridge.

“By modeling the behavior of seismic waves in Earth’s mantle, we discovered a transition inside the plate from the top, where the rocks didn’t deform or flow very much, to the bottom of the plate, where they are more strongly deformed by tectonic forces,” Beghein said. “This transition corresponds to a boundary between the layers that we can image with seismology and that we attribute to changes in rock composition.”

Oceanic plates form at ocean ridges and disappear into the Earth’s mantle, a process known as subduction. Among geoscientists, there is still considerable debate about what drives this evolution. Beghein and her research team advanced our understanding of how oceanic plates form and evolve as they age by using and comparing two sets of seismic data; the study revealed the presence of a compositional boundary inside the plate that appears to be linked to the formation of the plate itself.

New study reveals insights on plate tectonics, the forces behind earthquakes, volcanoes

The Earth's outer layer is broken into moving, interacting plates whose motion at the surface generates most earthquakes, creates volcanoes and builds mountains. In this image, the orange layer represents the deformable, warm asthenosphere in which there is active mantle flow. The green layer is the lithospheric plate, which forms at the mid ocean ridge, then cools down and thickness as it moves away from the ridge. The cooling of the plate overprints a compositional boundary that forms at the ridge by dehydration melting and is preserved as the plate ages. The more easily deformable, hydrated rocks align with mantle flow. The directions of past and present-day mantle flow can be detected by seismic waves, and changes in the alignment of the rocks inside and at the bottom of the plate can be used to identify layering. -  Nicholas Schmerr/University of Maryland
The Earth’s outer layer is broken into moving, interacting plates whose motion at the surface generates most earthquakes, creates volcanoes and builds mountains. In this image, the orange layer represents the deformable, warm asthenosphere in which there is active mantle flow. The green layer is the lithospheric plate, which forms at the mid ocean ridge, then cools down and thickness as it moves away from the ridge. The cooling of the plate overprints a compositional boundary that forms at the ridge by dehydration melting and is preserved as the plate ages. The more easily deformable, hydrated rocks align with mantle flow. The directions of past and present-day mantle flow can be detected by seismic waves, and changes in the alignment of the rocks inside and at the bottom of the plate can be used to identify layering. – Nicholas Schmerr/University of Maryland

The Earth’s outer layer is made up of a series of moving, interacting plates whose motion at the surface generates earthquakes, creates volcanoes and builds mountains. Geoscientists have long sought to understand the plates’ fundamental properties and the mechanisms that cause them to move and drift, and the questions have become the subjects of lively debate.

A study published online Feb. 27 by the journal Science is a significant step toward answering those questions.

Researchers led by Caroline Beghein, assistant professor of earth, planetary and space sciences in UCLA’s College of Letters and Science, used a technique called seismic tomography to study the structure of the Pacific Plate – one of eight to 12 major plates at the surface of the Earth. The technique enabled them to determine the plate’s thickness, and to image the interior of the plate and the underlying mantle (the layer between the Earth’s crust and outer core), which they were able to relate to the direction of flow of rocks in the mantle.

“Rocks deform and flow slowly inside the Earth’s mantle, which makes the plates move at the surface,” said Beghein, the paper’s lead author. “Our research enables us to image the interior of the plate and helps us figure out how it formed and evolved.” The findings might apply to other oceanic plates as well.

Even with the new findings, Beghein said, the fundamental properties of plates “are still somewhat enigmatic.”

Seismic tomography is similar to commonly used medical imaging techniques like computed tomography, or CT, scans. But instead of using X-rays, seismic tomography employs recordings of the seismic waves generated by earthquakes, allowing scientists to detect variations in the speed of seismic waves inside the Earth. Those variations can reveal different layers within the mantle, and can help scientists determine the temperature and chemistry of the mantle rocks by comparing observed variations in wave speed with predictions from other types of geophysical data.

Seismologists often use other types of seismic data to identify this layering: They detect seismic waves that bounce off the interface that separates two layers. In their study, Beghein and co-authors compared the layering they observed using seismic tomography with the layers revealed by these other types of data. Comparing results from the different methods is a continuing challenge for geoscientists, but it is an important part of helping them understand the Earth’s structure.

“We overcame this challenge by trying to push the observational science to the highest resolutions, allowing us to more readily compare observations across datasets,” said Nicholas Schmerr, the study’s co-author and an assistant research scientist in geology at the University of Maryland.

The researchers were the first to discover that the Pacific Plate is formed by a combination of mechanisms: The plate thickens as the rocks of the mantle cool, the chemical makeup of the rocks that form the plate changes with depth, and the mechanical behavior of the rocks change with depth and their proximity to where the plate is being formed at the mid-ocean ridge.

“By modeling the behavior of seismic waves in Earth’s mantle, we discovered a transition inside the plate from the top, where the rocks didn’t deform or flow very much, to the bottom of the plate, where they are more strongly deformed by tectonic forces,” Beghein said. “This transition corresponds to a boundary between the layers that we can image with seismology and that we attribute to changes in rock composition.”

Oceanic plates form at ocean ridges and disappear into the Earth’s mantle, a process known as subduction. Among geoscientists, there is still considerable debate about what drives this evolution. Beghein and her research team advanced our understanding of how oceanic plates form and evolve as they age by using and comparing two sets of seismic data; the study revealed the presence of a compositional boundary inside the plate that appears to be linked to the formation of the plate itself.

What sculpted Africa’s margin?

Break-up of the supercontinent Gondwana about 130 Million years ago could have lead to a completely different shape of the African and South American continent with an ocean south of today’s Sahara desert, as geoscientists from the University of Sydney and the GFZ German Research Centre for Geosciences have shown through the use of sophisticated plate tectonic and three-dimensional numerical modelling. The study highlights the importance of rift orientation relative to extension direction as key factor deciding whether an ocean basin opens or an aborted rift basin forms in the continental interior.

For hundreds of millions of years, the southern continents of South America, Africa, Antarctica, Australia, and India were united in the supercontinent Gondwana. While the causes for Gondwana’s fragmentation are still debated, it is clear that the supercontinent first split along along the East African coast in a western and eastern part before separation of South America from Africa took place. Today’s continental margins along the South Atlantic ocean and the subsurface graben structure of the West African Rift system in the African continent, extending from Nigeria northwards to Libya, provide key insights on the processes that shaped present-day Africa and South America. Christian Heine (University of Sydney) and Sascha Brune (GFZ) investigated why the South Atlantic part of this giant rift system evolved into an ocean basin, whereas its northern part along the West African Rift became stuck.

“Extension along the so-called South Atlantic and West African rift systems was about to split the African-South American part of Gondwana North-South into nearly equal halves, generating a South Atlantic and a Saharan Atlantic Ocean”, geoscientist Sascha Brune explains. “In a dramatic plate tectonic twist, however, a competing rift along the present-day Equatorial Atlantic margins, won over the West African rift, causing it to become extinct, avoiding the break-up of the African continent and the formation of a Saharan Atlantic ocean.” The complex numerical models provide a strikingly simple explanation: the larger the angle between rift trend and extensional direction, the more force is required to maintain a rift system. The West African rift featured a nearly orthogonal orientation with respect to westward extension which required distinctly more force than its ultimately successful Equatorial Atlantic opponent.

What sculpted Africa’s margin?

Break-up of the supercontinent Gondwana about 130 Million years ago could have lead to a completely different shape of the African and South American continent with an ocean south of today’s Sahara desert, as geoscientists from the University of Sydney and the GFZ German Research Centre for Geosciences have shown through the use of sophisticated plate tectonic and three-dimensional numerical modelling. The study highlights the importance of rift orientation relative to extension direction as key factor deciding whether an ocean basin opens or an aborted rift basin forms in the continental interior.

For hundreds of millions of years, the southern continents of South America, Africa, Antarctica, Australia, and India were united in the supercontinent Gondwana. While the causes for Gondwana’s fragmentation are still debated, it is clear that the supercontinent first split along along the East African coast in a western and eastern part before separation of South America from Africa took place. Today’s continental margins along the South Atlantic ocean and the subsurface graben structure of the West African Rift system in the African continent, extending from Nigeria northwards to Libya, provide key insights on the processes that shaped present-day Africa and South America. Christian Heine (University of Sydney) and Sascha Brune (GFZ) investigated why the South Atlantic part of this giant rift system evolved into an ocean basin, whereas its northern part along the West African Rift became stuck.

“Extension along the so-called South Atlantic and West African rift systems was about to split the African-South American part of Gondwana North-South into nearly equal halves, generating a South Atlantic and a Saharan Atlantic Ocean”, geoscientist Sascha Brune explains. “In a dramatic plate tectonic twist, however, a competing rift along the present-day Equatorial Atlantic margins, won over the West African rift, causing it to become extinct, avoiding the break-up of the African continent and the formation of a Saharan Atlantic ocean.” The complex numerical models provide a strikingly simple explanation: the larger the angle between rift trend and extensional direction, the more force is required to maintain a rift system. The West African rift featured a nearly orthogonal orientation with respect to westward extension which required distinctly more force than its ultimately successful Equatorial Atlantic opponent.

DNA test better than standard screens in identifying fetal chromosome abnormalities

A study in this week’s New England Journal of Medicine potentially has significant implications for prenatal testing for major fetal chromosome abnormalities. The study found that in a head-to-head comparison of noninvasive prenatal testing using cell free DNA (cfDNA) to standard screening methods, cfDNA testing (verifi® prenatal test, Illumina, Inc.) significantly reduced the rate of false positive results and had significantly higher positive predictive values for the detection of fetal trisomies 21 and 18.

A team of scientists, led by Diana W. Bianchi, MD, Executive Director of the Mother Infant Research Institute at Floating Hospital for Children at Tufts Medical Center, reports the results of their clinical trial using non-invasive cell-free DNA prenatal testing in a general obstetrical population of pregnant women, in an article entitled “DNA sequencing versus standard prenatal aneuploidy screening.”

The multi-center, blinded study analyzed samples from 1,914 pregnant women, and found that noninvasive cfDNA testing had a ten-fold improvement in the positive predictive value for trisomy 21, commonly known as Down syndrome, compared to standard prenatal aneuploidy screening methods (aneuploidy is a term for one or more extra or missing chromosomes). Importantly, the cfDNA test performed consistently well in a general population of pregnant women, regardless of their risk for fetal chromosomal abnormalities. Previous studies have shown that the tests were more accurate for women who had higher risks for fetal chromosomal abnormalities, but this was the first time that the cfDNA tests were compared in a general obstetrical population to the variety of blood and ultrasound tests that comprise the current standard of care in the United States.

“We found that the major advantage of noninvasive prenatal DNA testing was the significant reduction of the false positive rate,” said Bianchi. “Prenatal testing using cell-free DNA as a primary screen could eliminate the need for many of the invasive diagnostic procedures (such as amniocentesis) that are performed to confirm a positive screen.”

Prenatal screening for fetal aneuploidy is recommended by the American College of Obstetricians and Gynecologists as part of routine prenatal care. Researchers compared current standard noninvasive aneuploidy testing techniques – serum biochemical assays and nuchal translucency measurements using ultrasound – with a noninvasive, cell-free DNA test. Serum biochemical assays identify biomarkers for chromosomal abnormalities while nuchal translucency measurements use ultrasound examinations to measure the thickness of a space at the back of the baby’s neck. With Down syndrome, more fluid is present, making the space appear thicker. Cell-free DNA testing works by mapping and counting DNA fragments in a mother’s blood sample and comparing the measurements to normal reference samples. The cell-free DNA is obtained through a simple blood draw from the mother after 10 weeks of pregnancy.

The study’s endpoint was a comparison of false positive rates for trisomies 21 and 18 between the two methods. The false positive rate for combined trisomies 18 and 21 among those undergoing DNA testing was 0.45 percent while the rate for standard testing was 4.2 percent, a statistically significant difference.

Another comparison was made for positive predictive value of test results: DNA results for trisomy 21 had a predictive value of 45.5 percent compared to 4.2 percent in standard testing; DNA results for trisomy 18 had a predictive value of 40.8 percent compared to 8 percent for standard testing, a significant improvement.

“A strength of our study is that it was conducted in a variety of clinical settings that mirror real-world medical practices,” said Bianchi. “The majority of the patients in the study were less than 30 years old, were having their first baby, and conceived spontaneously. Our study population was racially and ethnically diverse, which also makes our results very relevant to actual clinical practice. We also obtained pregnancy outcome information on every patient in the study.”

Dr. Bianchi is Founding Executive Director of the Mother Infant Research Institute at Tufts Medical Center, Vice Chair for Pediatric Research at Floating Hospital for Children, Natalie V. Zucker Professor of Pediatrics, Obstetrics and Gynecology at Tufts University School of Medicine, and a member of the genetics program faculty at the Sackler School of Graduate Biomedical Science at Tufts University. She is a member of the Institute of Medicine, a branch of the National Academies.

DNA test better than standard screens in identifying fetal chromosome abnormalities

A study in this week’s New England Journal of Medicine potentially has significant implications for prenatal testing for major fetal chromosome abnormalities. The study found that in a head-to-head comparison of noninvasive prenatal testing using cell free DNA (cfDNA) to standard screening methods, cfDNA testing (verifi® prenatal test, Illumina, Inc.) significantly reduced the rate of false positive results and had significantly higher positive predictive values for the detection of fetal trisomies 21 and 18.

A team of scientists, led by Diana W. Bianchi, MD, Executive Director of the Mother Infant Research Institute at Floating Hospital for Children at Tufts Medical Center, reports the results of their clinical trial using non-invasive cell-free DNA prenatal testing in a general obstetrical population of pregnant women, in an article entitled “DNA sequencing versus standard prenatal aneuploidy screening.”

The multi-center, blinded study analyzed samples from 1,914 pregnant women, and found that noninvasive cfDNA testing had a ten-fold improvement in the positive predictive value for trisomy 21, commonly known as Down syndrome, compared to standard prenatal aneuploidy screening methods (aneuploidy is a term for one or more extra or missing chromosomes). Importantly, the cfDNA test performed consistently well in a general population of pregnant women, regardless of their risk for fetal chromosomal abnormalities. Previous studies have shown that the tests were more accurate for women who had higher risks for fetal chromosomal abnormalities, but this was the first time that the cfDNA tests were compared in a general obstetrical population to the variety of blood and ultrasound tests that comprise the current standard of care in the United States.

“We found that the major advantage of noninvasive prenatal DNA testing was the significant reduction of the false positive rate,” said Bianchi. “Prenatal testing using cell-free DNA as a primary screen could eliminate the need for many of the invasive diagnostic procedures (such as amniocentesis) that are performed to confirm a positive screen.”

Prenatal screening for fetal aneuploidy is recommended by the American College of Obstetricians and Gynecologists as part of routine prenatal care. Researchers compared current standard noninvasive aneuploidy testing techniques – serum biochemical assays and nuchal translucency measurements using ultrasound – with a noninvasive, cell-free DNA test. Serum biochemical assays identify biomarkers for chromosomal abnormalities while nuchal translucency measurements use ultrasound examinations to measure the thickness of a space at the back of the baby’s neck. With Down syndrome, more fluid is present, making the space appear thicker. Cell-free DNA testing works by mapping and counting DNA fragments in a mother’s blood sample and comparing the measurements to normal reference samples. The cell-free DNA is obtained through a simple blood draw from the mother after 10 weeks of pregnancy.

The study’s endpoint was a comparison of false positive rates for trisomies 21 and 18 between the two methods. The false positive rate for combined trisomies 18 and 21 among those undergoing DNA testing was 0.45 percent while the rate for standard testing was 4.2 percent, a statistically significant difference.

Another comparison was made for positive predictive value of test results: DNA results for trisomy 21 had a predictive value of 45.5 percent compared to 4.2 percent in standard testing; DNA results for trisomy 18 had a predictive value of 40.8 percent compared to 8 percent for standard testing, a significant improvement.

“A strength of our study is that it was conducted in a variety of clinical settings that mirror real-world medical practices,” said Bianchi. “The majority of the patients in the study were less than 30 years old, were having their first baby, and conceived spontaneously. Our study population was racially and ethnically diverse, which also makes our results very relevant to actual clinical practice. We also obtained pregnancy outcome information on every patient in the study.”

Dr. Bianchi is Founding Executive Director of the Mother Infant Research Institute at Tufts Medical Center, Vice Chair for Pediatric Research at Floating Hospital for Children, Natalie V. Zucker Professor of Pediatrics, Obstetrics and Gynecology at Tufts University School of Medicine, and a member of the genetics program faculty at the Sackler School of Graduate Biomedical Science at Tufts University. She is a member of the Institute of Medicine, a branch of the National Academies.