Printed carbon perovskite solar cells have been described as a likely front runner to the market because they are extremely efficient at converting light to electricity, cheap and easy to make.

A major barrier to the large-scale manufacture and commercialisation of these cells is the solvents used to control crystallisation of the perovskite during fabrication: this is because they are made from unsustainable materials and are banned in many countries due to their toxicity and psychoactive effects.

SPECIFIC’s researchers have discovered that a non-toxic biodegradable solvent called γ-Valerolactone (GVL) could replace these solvents without impacting cell performance.

GVL’s list of advantages could improve the commercial viability of carbon perovskite solar devices:

• It is made from sustainable feedstocks
• There are no legal issues in its use around the world
• It is suitable for use in large-scale manufacturing processes
• It is non-toxic and biodegradable

Carys Worsley, who led the research as part of her doctorate, said:

“To be truly environmentally sustainable, the way that solar cells are made must be as green as the energy they produce. As the next generation of solar technologies approaches commercial viability, research to reduce the environmental impact of large-scale production will become increasingly important.”

Professor Trystan Watson, research group leader, added:

“Many problems need to be resolved before these technologies become a commercial reality. This solvent problem was a major barrier, not only restricting large-scale manufacture but holding back research in countries where the solvents are banned.

We hope our discovery will enable countries that have previously been unable to participate in this research to become part of the community and accelerate the development of cleaner, greener energy.”

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Investigators also detected human-made chemicals called perfluoroalkyl substances (PFAS) in the tissues of adult killer whales. Thresholds for health effects of PFAS in marine mammals are not established, but the chemical has been linked to reproductive and endocrine effects in wildlife. In addition, polychlorinated biphenyls (PCBs), which have long been banned, were detected in the blubber of 7 of the 8 killer whales in the study at levels that exceeded the proposed threshold for toxicological effects in marine mammals.

“Levels of pollutants in top predators give not only an indication of ecosystem health, but of the persistence of chemicals, passive mobility in the environment, and active biotransport with migrating animals,” the authors wrote. “Our results are relevant for the continued environmental monitoring of contaminants in the Arctic.”

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The work centers around a large gene responsible for an inner-ear protein, otoferlin. Mutations in otoferlin are linked to severe congenital hearing loss, a common type of deafness in which patients can hear almost nothing.

“For a long time otoferlin seemed to be a one-trick pony of a protein,” said Colin Johnson, associate professor of biochemistry and biophysics in the OSU College of Science. “A lot of genes will find various things to do, but the otoferlin gene had appeared only to have one purpose and that was to encode sound in the sensory hair cells in the inner ear. Small mutations in otoferlin render people profoundly deaf.”

In its regular form, the otoferlin gene is too big to package into a delivery vehicle for molecular therapy, so Johnson’s team is looking at using a truncated version instead.

Research led by graduate student Aayushi Manchanda showed the shortened version needs to include a part of the gene known as the transmembrane domain, and one of the reasons for that was unexpected: Without the transmembrane domain, the sensory cells were slow to mature.

“That was surprising since otoferlin was known to help encode hearing information but had not been thought to be involved in sensory cell development,” Johnson said.

Findings were published today in Molecular Biology of the Cell.

Scientists in Johnson’s lab have been working for years with the otoferlin molecule and in 2017 they identified a truncated form of the gene that can function in the encoding of sound.

To test whether the transmembrane domain of otoferlin needed to be part of the shortened version of the gene, Manchanda introduced a mutation that truncated the transmembrane domain in zebrafish.

Zebrafish, a small freshwater species that go from a cell to a swimming fish in about five days, share a remarkable similarity to humans at the molecular, genetic and cellular levels, meaning many zebrafish findings are immediately relevant to humans. Embryonic zebrafish are transparent and can be easily maintained in small amounts of water.

“The transmembrane domain tethers otoferlin to the cell membrane and intracellular vesicles but it was not clear if this was essential and had to be included in a shortened form of otoferlin,” Manchanda said. “We found that the loss of the transmembrane domain results in the sensory hair cells producing less otoferlin as well as deficits in hair cell activity. The mutation also caused a delay in the maturation of the sensory cells, which was a surprise. Overall the results argue that the transmembrane domain must be included in any gene therapy construct.”

At the molecular level, Manchanda found that a lack of transmembrane domain led to otoferlin failing to properly link the synaptic vesicles filled with neurotransmitter to the cell membrane, causing less neurotransmitter to be released.

“Our study suggests otoferlin’s ability to tether the vesicles to the cell membrane is a key mechanistic step for neurotransmitter release during the encoding of sound,” Manchanda said.

The National Institutes of Health supported the study.

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That theory, the “Oxygen Control Hypothesis,” suggests that the size of these early multicellular organisms was limited by the depth to which oxygen could diffuse into their bodies. The hypothesis makes a simple prediction that has been highly influential within both evolutionary biology and geosciences: Greater atmospheric oxygen should always increase the size to which multicellular organisms can grow.

It’s a hypothesis that’s proven difficult to test in a lab. Yet a team of Georgia Tech researchers found a way — using directed evolution, synthetic biology, and mathematical modeling — all brought to bear on a simple multicellular lifeform called a ‘snowflake yeast’. The results? Significant new information on the correlations between oxygenation of the early Earth and the rise of large multicellular organisms — and it’s all about exactly how much O2 was available to some of our earliest multicellular ancestors.

“The positive effect of oxygen on the evolution of multicellularity is entirely dose-dependent — our planet’s first oxygenation would have strongly constrained, not promoted, the evolution of multicellular life,” explains G. Ozan Bozdag, research scientist in the School of Biological Sciences and the study’s lead author. “The positive effect of oxygen on multicellular size may only be realized when it reaches high levels.”

“Oxygen suppression of macroscopic multicellularity” is published in the May 14, 2021 edition of the journal Nature Communications. Bozdag’s co-authors on the paper include Georgia Tech researchers Will Ratcliff, associate professor in the School of Biological Sciences; Chris Reinhard, associate professor in the School of Earth and Atmospheric Sciences; Rozenn Pineau, Ph.D. student in the School of Biological Sciences and the Interdisciplinary Graduate Program in Quantitative Biosciences (QBioS); along with Eric Libby, assistant professor at Umea University in Sweden and the Santa Fe Institute in New Mexico.

Directing yeast to evolve in record time

“We show that the effect of oxygen is more complex than previously imagined. The early rise in global oxygen should in fact strongly constrain the evolution of macroscopic multicellularity, rather than selecting for larger and more complex organisms,” notes Ratcliff.

“People have long believed that the oxygenation of Earth’s surface was helpful — some going so far as to say it is a precondition — for the evolution of large, complex multicellular organisms,” he adds. “But nobody has ever tested this directly, because we haven’t had a model system that is both able to undergo lots of generations of evolution quickly, and able to grow over the full range of oxygen conditions,” from anaerobic conditions up to modern levels.

The researchers were able to do that, however, with snowflake yeast, simple multicellular organisms capable of rapid evolutionary change. By varying their growth environment, they evolved snowflake yeast for over 800 generations in the lab with selection for larger size.

The results surprised Bozdag. “I was astonished to see that multicellular yeast doubled their size very rapidly when they could not use oxygen, while populations that evolved in the moderately oxygenated environment showed no size increase at all,” he says. “This effect is robust — even over much longer timescales.”

Size — and oxygen levels — matter for multicellular growth

In the team’s research, “large size easily evolved either when our yeast had no oxygen or plenty of it, but not when oxygen was present at low levels,” Ratcliff says. “We did a lot more work to show that this is actually a totally predictable and understandable outcome of the fact that oxygen, when limiting, acts as a resource — if cells can access it, they get a big metabolic benefit. When oxygen is scarce, it can’t diffuse very far into organisms, so there is an evolutionary incentive for multicellular organisms to be small — allowing most of their cells access to oxygen — a constraint that is not there when oxygen simply isn’t present, or when there’s enough of it around to diffuse more deeply into tissues.”

Ratcliff says not only does his group’s work challenge the Oxygen Control Hypothesis, it also helps science understand why so little apparent evolutionary innovation was happening in the world of multicellular organisms in the billion years after the Great Oxygenation Event. Ratcliff explains that geologists call this period the “Boring Billion” in Earth’s history — also known as the Dullest Time in Earth’s History, and Earth’s Middle Ages — a period when oxygen was present in the atmosphere, but at low levels, and multicellular organisms stayed relatively small and simple.

Bozdag adds another insight into the unique nature of the study. “Previous work examined the interplay between oxygen and multicellular size mainly through the physical principles of gas diffusion,” he says. “While that reasoning is essential, we also need an inclusive consideration of principles of Darwinian evolution when studying the origin of complex multicellular life on our planet.” Finally being able to advance organisms through many generations of evolution helped the researchers accomplish just that, Bozdag adds.