The plastisphere: Colonised microbial hitchhikers and ecological food chain

Plastisphere, an analogous term related to the biosphere that delineates the thin layer of diverse metazoan and microbial lives that are thriving on the outside of plastic debris of the ocean. The plastics we use in our daily life get discarded into the ocean. These plastics break down into microplastics and nanoplastics. Microplastics and nanoplastics are already a great menace to our ocean environment.

 At the bottom of the ocean, plastic is the most prevalent debris. The rate of plastic pollution is so enormous that more than one million pieces of plastics are found per square kilometer in ocean accumulation zones.  

With the uptake of microplastic-containing seafood species, humans are becoming more vulnerable to oxidative stress, subsequent inflammation, genotoxicity, apoptosis and so on

No advanced technology was available at that time to study the plastisphere. An American and a Dutch research team collaboratively invented a microscopy technology named CLASI‐FISH. With the help of this technology, scientists portrayed the spatial organisation of microbes in the plastisphere.  

Environmentalists contemplate Plastic Marine Debris (PMD) as an Artificial Microbial Reef like the coral reef ecosystem. Primary producer, primary consumer and predator dwell in the plastisphere. The supreme species of the plastisphere is Vibrio cholerae, particularly in summer and the most common types of bacteria found in the plastisphere are Proteobacteria, Cyanobacteria and Bacteroidetes. According to scientists, more than 1000 species of microbes are found on this minuscule plastic. 

Plastic is the novel ecological habitat for the microbes in the ocean. The hydrophobicity of plastic facilitates microbial growth by encouraging the wide range of metabolic activities of microbes. In the oligotrophic zone of the ocean, the hydrocarbon from plastic provides the nutrient for the survival of these microbes. In a research study, it is briefed that 1g PMD contains 6.6% (0.06g/g) of microbial biomass whereas seawater the amount is only 0.01g/1000l. 

Plastic is the ideal ship for microbes as plastics are buoyant and move from one place to another place. Long-distance movements of the plastics enable the microbes to move from one ecosystem to another and act as a potential reservoir of invasive species. Hence, the community of the plastisphere is both physically and chemically different from the ambient water body. 

The colonised community also differs from the autochthonous substrates in the upper layer of the ocean. The main drivers behind this disparity are spatial and habitational conditions and seasonal effects. 

Without adequate processing municipal wastes initially get into the river; afterwards, these get mixed into the ocean which becomes the major source of microplastic in the ocean. Moreover, the sewage effluent contains various kinds of opportunistic pathogenic bacteria which eventually end up in the ocean. The biofilm coat of the plastisphere gives a lucrative look and tangy smell to the microplastic, thus mistaken as food by marine organisms. 

In a research study, it is prognosticated that, microplastics are the vector for transporting pathogenic microbes into seafood. Mussels, oysters take food in the filter-feeding method and these filter-feeding mechanisms make them susceptible to the uptake of microplastics. Resultantly fragments of plastics, pellets, films are found in the stomach of these species. 

However, the microbes in the plastisphere also create multifarious diseases in this seafood species. The plastisphere community possesses a detrimental effect on the body of these seafood species. Vibrio sp is the perfect paradigm of such an incident. Vibrio sp causes disease in bivalve and results in mass mortality in the bivalve population. Aeromonas sp in the plastisphere community harbors various kinds of fish pathogens. 

Again, harmful algal bloom (HABs) creating algae Alexandrium taylori, Ostreopsis and Coolia sp have also been found in the community. Recently, Tenacibaculum sp of bacteria has been identified which causes diseases in fish. 

One of the most astonishing facts about the plastisphere community is that some of the bacteria are antibiotic and metal resistant. In the plastisphere community microbes can easily transfer antibiotic-resistance genes, metal-tolerance or sequestration genes and virulence factors.

Adam Martiny, an environmental microbiologist at the University of California, says "It's unlikely that terrestrial bacteria can survive for long at sea, but because bacteria can swap DNA with each other, genes for antibiotic resistance can be passed to other bacteria". The impact of the plastisphere community is not only bound in seafood species, they also have dramatic effects on the human body. With the uptake of microplastic-containing seafood species, humans are becoming more vulnerable to oxidative stress, subsequent inflammation, genotoxicity, apoptosis and so on.

Moreover, pathogenic species of the plastisphere can facilitate the growth of specific groups in the lungs or GIT which results in disarray with microbial colonies.  Even though seafood innards are discarded before human consumption, some species of small fish, bivalves and echinoderms are eaten whole. This poses a threat of microplastic accumulation in humans. 

Each passing day, the production of plastic is going upwards with the demand, resulting in growing amounts of micro and nanoplastics in seafood and fisheries products. "One of the benefits of understanding the plastisphere right now and how it interacts with biota in general, is that we are better able to inform scientists on how to make better materials and, if they do get out to sea, have the lowest impact possible," said Mincer, one of the scientists who discovered plastisphere. 

Lastly, more detailed studies and research should be done on the plastisphere community to fulfill the knowledge gaps. All should come and act as one to combat this fight. 

Disclaimer: This article first appeared on Bloomberg, and is published by special syndication arrangement.