The Paper: Kirstein IV, S Kirmizi, A Wichels, A Garin-Fernandez, R Erler, M Löder & G Gerdts. 2016. Dangerous hitchhikers? Evidence for potentially pathogenic Vibrio spp. on microplastic particles. Marine Environmental Research 120:1-8.
Plastics in The Ocean
By this point, most people are aware of the detrimental effect that plastic waste is having on our oceans. The Great Pacific Garbage Patch is nearly a household name, and photos of the massive amount of plastic waste found in the stomachs of dead animals is becoming far too common. Worldwide production of plastic has reached 311 million tons per year (about 70,000 water bottles for every US citizen), and due to improper disposal, is now the fastest growing type of human produced material entering the world’s oceans. These plastics (synthetic polymers) are very durable and do not decompose in the ocean. Instead, they become brittle and break up into very small (less than 5mm in diameter) pieces known as microplastics (Fig. 1) that can travel over great distances with ocean currents and wind.
Much of the wildlife impact has been focused on larger pieces of plastic because they are either mistaken by animals for food, or can cause animals to become entangled. However, these microplastics can be just as dangerous (although harder to photograph) because they are accidentally ingested and can accumulate in the digestive system and cause serious problems and death. Additionally, microplastics are now found to contain an entire ecosystem of bacteria and algae called the “Plastisphere”. While most of the organisms living on these tiny particles are harmless, new research is showing that they are a very good environment for the growth of bacteria that are harmful to humans and other wildlife.
A team of German researchers, led by Dr. Inga Kirstein, has conducted the first research that specifically investigates the harmful bacteria that may be populating these microplastics. They looked for bacteria in the genus Vibrio that contains several species responsible for illness in humans, including cholera. In particular, they targeted Vibrio parahaemolyticus, Vibrio vulnificus, and Vibrio cholera, all of which are known as water-borne pathogens. While these organisms occur naturally in sediments, estuaries, and marine coastal waters, their concentration on the surface of microplastics and subsequent long range dispersal make them more of a danger to humans than they would normally be. Instead of just needing to worry about eating undercooked seafood from an isolated location, they would have the potential of infecting very large geographic areas and cause problems for a major human food source.
Dr. Kirstein and team collected plastic from surface water using a fine-weave net at 62 sampling locations in the Baltic and North Sea. The particles were sorted visually by polymer type and rinsed to remove any of the loosely attached organisms. They were then placed in separate containers and incubated in several stages to selectively favor the growth of Vibrio bacteria. Once this was complete, a species-level analysis was done to differentiate the Vibrio parahaemolyticus, Vibrio vulnificus, and Vibrio cholera using a technique (MALDI-TOF MS) that looks for proteins specifically associated with these three organisms. Additionally, this species level analysis was verified by targeting specific regions of DNA that can be directly attributed to each of the three pathogens. Finally, each of the tiny particles were analyzed using optical spectrometry (distinguishing different chemical compounds based on their light pattern) to definitively label the polymer type of each particle collected.
What They Found
First, the majority of the particles collected were polyethylene, comprising over 40% of collected particles at all of the sites (Fig. 2; dark blue portion of pie chart). This is the most common plastic manufactured, and it is used to make most packaging materials including plastic bottles. Almost all of these particles were cracked and pitted, indicating significant weathering and had thick layers of colonizing organisms on their surface.
Next the researchers analyzed water samples that were taken from each of the sampling locations. This analysis was done to compare the bacterial communities of the surrounding waters to the microplastic particles found at each location. It has been postulated that this “Plastisphere” is a distinctly different community than the water that surrounds it, and the researches were out to determine if this was the case. They found that all three pathogens were present in a large number of these samples and specifically found in the samples close to shore and estuaries of the North Sea (Fig. 3; red, orange, and dark blue circles).
Finally, the microplastic particles contained many Vibrio species, but only one of the pathogenic species (Vibrio parahaemolyticus) was found (Fig. 3; red triangles). This is the organism most closely associated with food poisoning from consuming raw or undercooked seafood (usually oysters).
Why Is This Important
As humans continue to increase in population and pollute the environment, the consequences will be multi-layered and far-reaching. The impact of plastic in our oceans has already been shown to be detrimental to marine life, and this has an effect on us in more ways than are immediately obvious. Plastic pollution can be ingested, causing death from internal, digestive tract problems. It can entangle animals and lead to suffocation. These can lead to disruptions in the food web and cause the loss of important fisheries. And now, it has been shown that plastic is a viable home for pathogenic bacteria that can travel on wind and ocean currents and become a major source of disease. We only have one planet and if actions are not taken to curb its destruction, it will no longer be habitable by humans in a very short amount of time.