Billions of people still suffer from hunger and food insecurity worldwide. Meanwhile, microbial contamination causes a third of global food waste annually, resulting in major economic losses and illnesses. Although antibiotics and pesticides help control contamination, their excessive use can promote bacterial resistance or leave toxic residues. 

One alternative uses materials that generate highly reactive forms of oxygen when exposed to light, called photocatalysts, to prolong food freshness. These molecules kill bacteria by damaging their cell components in a process called photodynamic inactivation or PDI. However, current PDI systems rely on energy-intensive lasers and long exposure times because the bacteria’s protective cell membranes block reactive oxygen molecules. As a result, the systems don’t kill bacteria effectively and risk overheating food, affecting its freshness and nutritional value.

Scientists at Zhejiang University in China thought that it would be possible to achieve a PDI system using accessible, free sunlight with the right photocatalyst. Moreover, they also wanted to integrate this photocatalyst into food packaging to combat microbes during storage. 

To make the photocatalyst, the researchers mixed water with a glue-like plant fiber that provides structural support, called pectin, and a chemical from plant seeds that supplies phosphorus, called phytic acid. Then they heated the mixture in a sealed reactor at 220ºC (428ºF) for 5 hours to form tiny structures composed of a carbon core surrounded by a phosphorus-rich shell called phosphorus-modified carbonized polymer dots or PCDs.

To incorporate the PCDs into film packaging, the researchers dissolved equal amounts of a plant fiber from konjac, called glucomannan, and another plant-derived molecule, called carboxymethylcellulose, in warm water to form a network of entangled molecular chains. Then, they added 1.5 milligrams of PCD per milliliter to this mixture, which linked the chains together like molecular fasteners. Finally, they added a moisture-binding chemical called glycerin to prevent brittleness. The researchers cast this mixture onto separate Petri dishes and dried them, forming thin, plastic-like PCD films.

To test the films, the researchers placed Escherichia coli bacteria between 2 sterilized film sheets and exposed the samples to either darkness or simulated sunlight for 20 minutes. They then transferred the microbes onto agar plates and incubated them for 15 hours, allowing surviving bacteria to form visible colonies. They compared the number of bacterial colonies with those of untreated samples to calculate the percentage of bacteria the films eliminated in each environment. 

Tests under darkness showed that the films eliminated about 60% of the bacteria. The researchers attributed this result to the positive electrical charge of PCDs, which attracts the bacteria’s negatively charged cell surfaces. The electrical attraction stresses their cell membranes, interfering with essential life processes. This result suggested that the films use a separate charge-based antibacterial mechanism apart from PDI, which requires light to work.

Under simulated sunlight, the films eliminated nearly 100% of the bacteria. The researchers identified 2 principal mechanisms causing this. First, the PCDs acted as tiny heaters that generated localized heat, which stretched holes in the bacterial membranes, allowing contents to leak out of their cells through a process called photoporation. Second, the PCDs generated reactive oxygen molecules that could then penetrate the bacteria. Once inside the cells, these molecules irreversibly damage the bacteria’s internal components and genetic material through PDI. 

The researchers also investigated whether PCD films could serve as food packaging by using them to wrap fresh strawberries. Compared with conventional nonbiodegradable polyethylene packaging where visible rotting occurred, the PCD films kept the strawberries fresh for more than 4 days by suppressing bacterial growth and regulating moisture levels. When the team tested whether the films were toxic, they found that the films are safe for humans and compatible for food applications. They also buried the films in soil for 24 days and found that they degraded by 78%, demonstrating biodegradability suitable for packaging fresh foods.

The team concluded that PCD films could be a biodegradable food packaging that combines plant-based materials with multiple antibacterial strategies. The films retained antibacterial activity in darkness and became more effective under sunlight through the combined effects of photoporation and PDI. These findings demonstrated that by combining multiple mechanisms into a single material, researchers can create multifunctional food packaging that remains effective across different storage conditions.

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Astronomers have long wondered whether life on Earth might have had origins somewhere else in the cosmos. The idea that the key ingredients for life, or even simple organisms, might be carried through space by non-animate objects—a concept known as panspermia—has been proposed as one way such “seeding” of life on Earth might have occurred.

But what if it could also happen in reverse? In other words, what if life were one day found on an alien moon, which could later be traced back to Earth?

This is the very idea presented in a new study that explores the provocative idea that Jupiter’s frozen moon Europa may not only be hospitable, but that life from Earth could be thriving there.

In the new study, published in the International Journal of Astrobiology, astrophysicist Zaza Osmanov of the Free University of Tbilisi explored whether Earthly bacteria might have been able to escape our planet by traveling on microscopic dust particles, which, after escaping Earth’s gravity, could have drifted through space until they reached Europa.

There, a vast subsurface ocean is believed to exist beneath the moon’s icy crust, meaning that any simple organisms capable of escaping from Earth on tiny spacefaring rafts of dust might have found their way to a new home, and one that could support life.

Panspermia, but in Reverse

The long-debated idea of panspermia already presents the general idea for how this might work. However, Osmanov’s study investigates this idea in reverse order: not only might life on Earth have originated from elsewhere, but our planet could also hypothetically be the source of similar “seeding” events that might occur on alien worlds.

Based on mathematical models, Osmanov calculated how bacteria-rich dust grains could be launched into space, resulting from collisions with incoming dust in Earth’s upper atmosphere. Upon escaping the planet’s gravity, some of these bacteria might be able to sail along toward distant locales like Europa with the help of pressure generated by solar radiation—essentially the same concept as a solar light sail spacecraft, albeit much smaller.

With the help of solar radiation and occasional gravitational interactions, Osmanov theorizes that some particles might eventually be “steered” by such natural processes over time, eventually making their way to Jupiter.

Tiny Earthling Alien Invaders

Based on Osmanov’s estimates, there could potentially be as many as hundreds of millions of Earth-originating dust particles that might make their way to Europa every second. That’s a significant number, and although he estimates that the majority would be destroyed on impact, a small fraction could arrive at extremely shallow angles, which he believes may be able to survive landing on Europa’s surface.

However, even if a few bacterial invaders managed to survive, the next challenge they would face would be to reach the moon’s ocean that astronomers believe to be concealed beneath its icy exterior. Based on past studies, tidal forces generated by the massive host planet Jupiter offer a solution: such events are believed to likely cause fractures in Europa’s icy shell, which lead to the creation of entry points where surface materials might be capable of migrating downward.

Adding to this, Osmanov also points to instances where ice melting may also provide a means for the movement of material from the surface down into the moon’s hidden ocean. Over periods of thousands of years, some of these tiny bacterial invaders might make their way past the harsh surface environment and down into the moon’s far more hospitable subsurface ocean.

Osmanov estimates that there may be considerable numbers of Earth-derived particles that could reach Europa’s ocean over geological timescales. This could mean that terrestrial particles, Earthly microbes that have made the journey, may have had time to establish themselves as microbial colonists—if, of course, current presumptions about the moon’s conditions for supporting life are correct.

While the theory remains speculative, and Osmanov concedes that it cannot be tested directly at present, it suggests something fascinating: that the eventual discovery of life on an alien world could have ancestral links to our own planetary home.

Osmanov’s recent study, “Earth as a potential source of life for Europa’s subsurface ocean,” appeared in the journal International Journal of Astrobiology.

Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. A longtime reporter on science, defense, and technology with a focus on space and astronomy, he can be reached at micah@thedebrief.org. Follow him on X @MicahHanks, and at micahhanks.com.