Microbes Colonize a New Marine Ecosystem: The ‘Plastisphere’

Microbes Colonize a New Marine Ecosystem: The ‘Plastisphere’

WOODS HOLE, Massachusetts, June 30, 2013 (ENS) - Multitudes of microbes are colonizing bits of plastic that have polluted the oceans - a vast new human-made flotilla of microbial communities that marine scientists have dubbed the "plastisphere."

Complex communities of microbes 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.

Published online in the journal "Environmental Science & Technology," the study revealing these microbial communities for the first time says the plastisphere is a new ecological habitat in the ocean.

"Plastisphere communities are distinct from surrounding surface water, implying that plastic serves as a novel ecological habitat in the open ocean," the study states.

Plastics accumulate in all of the world's five oceanic gyres formed by winds and currents in the North and South Atlantic, the North and South Pacific and the Indian oceans.

In these gyres, plastic bags, plastic food and water containers, toys, six-pack rings, condoms, fishing lines and nets discarded on land or at sea float and whirl endlessly, breaking down into smaller and smaller pieces but never completely disappearing.

A collaborative team of scientists from three institutions based in Woods Hole analyzed millimeter-sized fragments of this plastic debris skimmed with fine-scale nets from the sea surface at several locations in the North Atlantic Ocean.

Erik Zettler from Sea Education Association, Linda Amaral-Zettler from the nonprofit Marine Biological Laboratory, and Tracy Mincer from Woods Hole Oceanographic Institution investigated the plastisphere for this study.

"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.

In fact, she says, the initial discoveries raise a host of questions about the structure and functions of the newly discovered plastisphere.

"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 scientists want to know.

"Are they sinking to the bottom of the ocean? Are they being ingested? If they're being ingested, what impact does that have?"

Undergraduate students collected and processed the samples as part of their research on cruises offered by Sea Education Association, a nonprofit educational institution.

Using scanning electron microscopy and gene sequencing techniques, the investigators found at least 1,000 different types of bacterial cells on the plastic samples, including many species that have not yet been identified.

The cellular organisms found in the plastisphere included plants, algae, and bacteria that manufacture their own food; animals and bacteria that feed on them; predators that feed on these, and other organisms that establish synergistic relationships.

"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."

The scientists believe these communities are 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 that may be 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.

"Now we have to figure out what they are by [genetically] sequencing them and hopefully getting them into culture so we can do experiments," said Zettler.

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 sample 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.

Copyright Environment News Service (ENS) 2013. All rights reserved.

Cover photo: Suctorian ciliate covered with symbiotic bacteria, along with diatoms, and filaments on weathered and cracked microplastic debris. (Image courtesy of Erik Zettler, Sea Education Association)

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