bacteria nestle in pits on a piece of plastic
The dents in which the bacteria were found give scientists hope that they may be breaking down the plastic waste

New life discovered growing on plastic waste dubbed the ‘plastisphere’
by Penny Orbell  /  13 Nov 2013

Vast amounts of of plastic debris floating in the ocean are supporting new forms of microscopic life and whole new ecosystems. Scientists writing in the journal Environmental Science & Technology are collectively calling this new life the ‘plastisphere’. Previous studies have thoroughly outlined the harmful effects of plastic on animals such as fish, birds and other forms of marine life. However, none had fully assessed the effects of plastic on microscopic ocean dwellers. The team, which included Tracy Mincer at the Woods Hole Oceanographic Institution in Massachusetts and Linda Amaral-Zettler of the Marine Biological Laboratory in Woods Hole, used fine mesh nets to collect pieces of plastic — around 1 to 5mm in diameter — from sites in the North Atlantic Ocean.

Using a combination of high-resolution imaging and genetic sequencing, they discovered unique ecosystems living on two kinds of plastic, with communities composed of microbes that are genetically distinct from those on other natural surfaces in the surrounding waters, such as driftwood or feathers. The plastic communities were also more diverse than those in seawater samples, which are typically dominated by only a few species. “The organisms inhabiting the plastisphere were different from those in surrounding seawater, indicating that plastic debris acts as artificial ‘microbial reefs’,” said Mincer. “They supply a place that selects for and supports distinct microbes to settle and succeed.”

More than 1,000 species of microbes were found in the study, including plants, algae and bacteria, some of which remain unidentified. These communities typically had a natural order: with plant-like organisms at the bottom of the food chain and higher order creatures that feed on them. Other organisms that live in harmonious relationships with each other were also identified. “We’re not just interested in who’s there. We’re interested in their function, how they’re functioning in this ecosystem, how they’re altering this ecosystem, and what’s the ultimate fate of these particles in the ocean,” said Amaral-Zettler. “Are they sinking to the bottom of the ocean? Are they being ingested? If they’re being ingested, what impact does that have?” Electron microscope images also reveal that some bacterial members of the plastisphere were nestled in ‘pits’ on the plastic surface, supporting the idea that these organisms may actually be contributing to the degradation of the plastic.

Studies conducted over the last 22 years found that despite an increase in the production of plastics, the amount of plastic oceanic debris has remained relatively stable. The scientists hope that ‘pit formers’ are breaking down the plastic, though they caution that more experiments need to be conducted. “When we first saw the ‘pit formers’ we were very excited, especially when they showed up on multiple pieces of plastic of different types of resins,” said Zettler. “Now we have to figure out what they are by sequencing them and hopefully getting them into culture so we can do experiments.” As the research is in its infancy, it is difficult to speculate yet about the potential effects of the emerging plastisphere on marine ecological environments. Researchers are concerned that as the plastics, along with the unique micro-organisms they harbour, drift widely they have the potential to act as vectors for dispersal of harmful pest species or pollutants.

Bits of Plastic Marine Debris
Tiny bits and pieces of plastic can be found throughout the ocean, like these collected from the open ocean by net

A new marine ecosystem
by Erik Zettler  /  07/30/2013

Any floating object in the ocean tends to attract life; fishermen know this and deploy floating buoys to concentrate fish for harvesting. Plastic marine debris is no different and, at microscopic scales, microbes such as bacteria, algae and other single-celled organisms gather around and colonize plastic and other objects floating in water. Even small pieces of plastic marine debris the size of your pinky nail can act as microbe aggregating devices. We call this community of microbes growing as a thin layer of life (a biofilm) on the outside of plastic the “plastisphere,” analogous to the layer of life on the outside of planet Earth called the “biosphere.” Using plastic samples collected during Sea Education Association student research cruises, we are studying what kinds of microbes live in the plastisphere, how they colonize the surfaces of plastic, and how they might affect marine ecosystems.

Scanning electron micrographs reveal a complex geography of microbial life on the cracked and pitted surfaces of plastic pieces that have been aging and weathering in the ocean. Tracy Mincer, a scientist at Woods Hole Oceanographic Institution studying this new community, refers to it as a “microbial reef” because it is a complete ecosystem with primary producers (like plants), grazers, predators, and decomposers, just like the community of larger organisms found on the complex surface of a coral reef. One of our most interesting discoveries is a type of cell that we call “pit formers,” spherical cells that appear to be embedded in the surface of the plastic pieces. These may somehow contribute to the breakdown of plastic marine debris, which would have implications for what happens to plastic in the ocean over the long term.

Linda Amaral-Zettler at the Marine Biological Lab used genetic techniques that allow us to look at the microbes’ DNA to reveal surprisingly high biodiversity, with over 1,000 kinds of microbes on a single small piece of plastic only 5mm or less across. What’s even more remarkable is that some of the organisms are not normally encountered in the open ocean, but are able to survive there by clinging to the plastic bits. The genetic work also turned up unexpectedly large numbers of the common marine bacterial genus Vibrio; most Vibrio are not harmful but some species can be associated with diseases in humans and animals. We are isolating and studying Vibrio cultures from marine plastic to see if any of them cause disease.

Because plastic persists for so long, microbes in the plastisphere can be transported long distances, making them a potential source of invasive species. If microbes are being moved around in the ocean from a variety of differing ecosystems, they could be impacting the native microbial populations and the larger organisms that depend on those microbes. The plastisphere could also modify plastic debris to make the plastic more, or less, harmful to marine ecosystems.

A film of Candida albicans fungal cells grown on a contact lens (top panel) is reduced to cellular debris (bottom panel) by a polymer-like material.

Material Made from Plastic Bottles Kills Drug-Resistant Fungus
IBM researchers have developed a new polymer-like material to treat fungal infections.
by Susan Young / December 9, 2013

A material made from plastic bottles can knock out a drug-resistant fungal infection that the Centers for Disease Control and Prevention predicts will become a more serious health problem in coming years. Antibiotic-resistant bacteria and fungi kill at least23,000 people in the U.S. alone each year, and many  of these microbial infections are acquired by people hospitalized for other reasons. Research groups around the world are exploring a variety of ways to address the problem, including hunting for novel kinds of antibiotics (see “Bacteria Battle Generates New Antibiotics”) and creating sutures coated with bacteria-killing viruses (see “Using Viruses to Kill Bacteria”).

Another approach involves using biologically active materials that punch holes in the membranes surrounding each microbial cell. These membrane-attacking compounds mimic one of the body’s natural defenses—antimicrobial peptides that insert themselves into a microbe’s outer membrane and break open the bug. IBM Research has developed such a compound—a small molecule that self-assembles into a polymer-like complex capable of killing Candida albicans fungi infecting the eyes of mice. The work was published today in Nature Communications. “Usually, it is difficult to make antifungal agents because fungal cells are very similar to human cells,” says Kenichi Kuroda, a materials chemist at the University of Michigan who is also working on antimicrobial materials. The challenge is that many microbe-killing drugs work by sabotaging a molecular process inside the pathogen’s cells. And while the molecular machinery of bacteria is usually sufficiently distinct from human cellular machinery to avoid overlapping effects, fungal cells are much closer.

The new IBM compound has not yet been tested in humans, but the researchers say that in mice with a Candida infection in their eyes, the compound killed the fungus more effectively than a widely used antifungal drug without causing harm. And whereas Candida developed resistance to an existing antifungal drug after six treatments, it did not develop resistance to the new compound even after 11 treatments, the team reports. That ability to avoid resistance may be thanks to the fact that the compound kills by disrupting the microbes’ outer membrane. Unlike antibiotics, which typically work slower and therefore enable a population of bacteria to evolve resistance to a drug’s function, “these kinds of biomaterials have a quick action,” says Kuroda, whose is also focusing on attacking microbial membranes.

IBM developed the polymer-like material using techniques that are well-established in microelectronics but relatively new to biology, says James Hedrick, the IBM Research materials scientist leading the work. The compound belongs to a branch of materials sometimes referred to as molecular glasses. The compound starts off as many individual small molecules, but in water, these individual molecules coalesce into a larger structure that is similar to a polymer, but with weaker bonds between each molecule. This means that the material degrades over time. “With time it’s going to fall apart, and going to pass through the body,” Hedrick says.  “You want them to do their business and then go away, and you don’t want them to accumulate in the body, in waterways, and in our food.”

The starting material comes from a common plastic known as PET. Hedrick says whenever he needs more starting material, he just goes to the nearest recycling bin in the San Jose-based IBM Research building, finds a plastic bottle, and cuts a piece of out of it. Working with collaborators in Singapore who handle the animal testing branch of the project, Hedrick says a similar compound can knock out an antibiotic-resistant bacterial infection known as MRSA. By injecting that compound into the tail veins of mice, the researchers have been able to clear a MRSA infection from their blood. “We can do many things with [these compounds],” says Hedrick. “We can make them into hydrogels to treat MRSA skin infections and they can go into everything from shampoo to mouthwash.”

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