Wynne Parry LiveScience Yahoo News 26 Jun 13;
For about four decades, it's been known that plastic is collecting in the open ocean. Now, scientists have found this debris harbors unique communities of microbes, and the tiny residents of this so-called plastisphere may help break down the marine garbage.
Inhabitants of the plastisphere include members of a group of bacteria, the vibrios, known to cause disease, and microbes known to break down the hydrocarbon bonds within plastics, genetic analysis revealed. But most important, the communities of microbes on the plastic pieces were quite different from those found in samples of surrounding seawater.
"It's not a piece of fly paper out there with things just sticking to it randomly," said study researcher Tracy Mincer, an associate scientist at the Woods Hole Oceanographic Institution, referring to the plastic. "There are specific groups of microbes that are attracted to that environment and are adhering to it and living on it."
Potential pathogens & plastic degraders
Vibrios accounted for nearly 24 percent of the residents on one of the six small pieces of plastic used in the study.
"Because most plastic originates from land it begs the question how far these vibrios are coming from. … And are they potential pathogens, not just of humans, but for animals, such as fish," said study researcher Linda Amaral-Zettler, an associate scientist at the Marine Biological Laboratory. Some species in the genus Vibrio cause disease, but it’s not clear what species were within the samples, since the analysis for this study did not identify individual species of bacteria.
Burrowed in
Meanwhile, microscope images revealed microbestucked into pits that conformed to the shape of their single-celled bodies. The pits suggest the microbes are perforating the plastic and accelerating the natural weathering process, breaking it down, Mincer said. (The researchers aren’t certain which bacteria are in the pits; most bacteria cannot be identified through microscope images.)
"Either the cells have to settle into the perfectly shaped pits or they have something to do with creating the pits," said study researcher Erik Zettler, associate dean and professor of oceanography at the Sea Education Association in Woods Hole, Mass.
If the microbes are indeed burrowing into the plastic, they may be doing so mechanically or they could be metabolizing, otherwise known as "eating," the plastic, Zettler said.
The presence of hydrocarbon-degrading bacteria, related to those that bloomed after the Deep Horizon oil spill, indicates that bacteria may indeed be responsible for the pits.
Good or bad for ocean life?
The scientists aren't sure if bacteria-aided breakdown of plastics is good or bad for ocean ecosystems.
Whereas smaller pieces may accelerate the removal of plastics from the oceans, they may also have negative consequences. Smaller trash bits have a larger surface area (and more contact with the surrounding water) relative to volume so they can release more of the pollutants that plastics can absorb.
These itsy bits of plastic are also morelikely to enter the bottom of food chains when animals such as tiny, floating creatures called zooplankton consume them,and accumulate in the predatorsat the top, Zettler said.
Much of the plastic debris in the ocean has been broken down into confetti-size pieces. During voyages in the North Atlantic, researchers and students onboard a Sea Education vessel collected bits of plastic for this study, which was published online by the journal Environmental Science & Technology on June 7.
This research is part of a National Science Foundation-funded project to study microbes living on marine plastic.
Going forward, Mincer is interested in finding the genetic mechanism that has enabled the plastic colonizers to attach to it so quickly and effectively.
"We think it may lead to a story of microbes adapting to a changing world," he said, pointing out that plastics are quite different from any surface upon which open ocean microbes would naturally settle.
Scientists Discover Thriving Colonies of Microbes in Ocean 'Plastisphere'
Science Daily 27 Jun 13;
June 27, 2013 — Scientists have discovered a diverse multitude of microbes colonizing and thriving on flecks of plastic that have polluted the oceans -- a vast new human-made flotilla of microbial communities that they have dubbed the "plastisphere."
In a study recently published online in Environmental Science & Technology, the scientists say the plastisphere represents a novel ecological habitat in the ocean and raises a host of questions: How will it change environmental conditions for marine microbes, favoring some that compete with others? How will it change the overall ocean ecosystem and affect larger organisms? How will it change where microbes, including pathogens, will be transported in the ocean?
The collaborative team of scientists -- Erik Zettler from Sea Education Association (SEA), Tracy Mincer from Woods Hole Oceanographic Institution (WHOI), and Linda Amaral-Zettler from the Marine Biological Laboratory (MBL), all in Woods Hole, Mass. -- analyzed marine plastic debris that was skimmed with fine-scale nets from the sea surface at several locations in the North Atlantic Ocean during SEA research cruises. Most were millimeter-sized fragments.
"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," says 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?"
Using scanning electron microscopy and gene sequencing techniques, they found at least 1000 different types of bacterial cells on the plastic samples, including many individual species yet to be identified. They included plants, algae, and bacteria that manufacture their own food (autotrophs), animals and bacteria that feed on them (heterotrophs), predators that feed on these, and other organisms that establish synergistic relationships (symbionts). These complex communities exist on plastic bits hardly bigger than the head of a pin, and they have arisen with the explosion of plastics in the oceans in the last 60 years.
"The organisms inhabiting the plastisphere were different from those in surrounding seawater, indicating that plastic debris acts as artificial 'microbial reefs," says Mincer. "They supply a place that selects for and supports distinct microbes to settle and succeed."
These communities are likely different from those that settle on naturally occurring floating material such as feathers, wood, and microalgae, because plastics offer different conditions, including the capacity to last much longer without degrading.
On the other hand, the scientists also found evidence that microbes may play a role in degrading plastics. They saw microscopic cracks and pits in the plastic surfaces that they suspect were made by microbes embedded in them, as well as microbes possibly capable of degrading hydrocarbons.
"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, who added that undergraduate students participating in SEA Semester cruises collected and processed the samples. "Now we have to figure out what they are by [genetically] sequencing them and hopefully getting them into culture so we can do experiments."
The plastic debris also represents a new mode of transportation, acting as rafts that can convey harmful microbes, including disease-causing pathogens and harmful algal species. One plastic sampled they analyzed was dominated by members of the genus Vibrio, which includes bacteria that cause cholera and gastrointestinal maladies.
The project was funded by a National Science Foundation Collaborative grant, a NSF TUES grant, and a Woods Hole Center for Oceans and Human Health Pilot award.
Journal Reference:
Erik R. Zettler, Tracy J. Mincer, Linda A. Amaral-Zettler. Life in the “Plastisphere”: Microbial Communities on Plastic Marine Debris. Environmental Science & Technology, 2013; 130619162220002 DOI: 10.1021/es401288x
