MICROPLASTICS – AN EMERGING VECTORS FOR MICROBES?
Dr Brindha S* and Dr Iqra Arif*
*PhD Scholar,
Department of Veterinary Public Health and Epidemiology,
College of Veterinary Sciences, GADVASU, Ludhiana
INTRODUCTION
Plastic pollution has become a global crisis, driven by the exponential growth in plastic production since the 1950s. Over the past 65 years, a staggering 8.3 billion tons of plastic has been produced, with 6.3 billion tons now existing as waste. Among the many concerning aspects of this issue is the pervasive presence of microplastics. These tiny synthetic particles, ranging from 1 µm to 5 mm in size, pose a significant environmental threat. They can be categorized as primary microplastics, intentionally manufactured for various purposes, or secondary microplastics, resulting from the breakdown of larger plastic debris. Microplastics have been detected in oceans, freshwater bodies, agricultural systems, the atmosphere, and even remote areas. This widespread contamination has given rise to the emergence of the “plastisphere,” an ecological phenomenon where plastic waste accumulates and creates an environment that promotes biofilm formation. This combination of microplastics, biofilm, and associated pollutants poses potential risks to microbial species distribution and ecosystem health. Addressing the challenges posed by microplastics and the plastisphere is crucial to mitigate the damaging impacts of plastic pollution on our planet.
The consequences of plastic pollution are particularly evident in marine ecosystems. Between 4.8 and 12.7 million tons of plastic entered the oceans in 2010 alone, and projections indicate a tenfold increase by 2025. This massive influx of plastic waste has led to at least 5.25 trillion pieces of plastic floating in our oceans. Marine life and ecosystems suffer as a result, with entanglement and ingestion causing harm and death among various species. Furthermore, the seafloor has become a significant sink for global plastics, creating the plastisphere environment. In this habitat, microbes are exposed to microplastic-associated pollutants, such as antibiotics and heavy metals, which are surrounded and protected by biofilms. This combination of factors can potentially alter the distribution of microbial species. Urgent action is required to address plastic pollution, mitigate the presence of microplastics, and protect marine ecosystems from the devastating effects of plastic waste.
MICROBIAL ASSOCIATION WITH MICROPLASTICS
Microplastics have been found to serve as substrates for the attachment of various microorganisms, including fungi, diatoms, algae, and bacteria. The attachment to surfaces offers numerous advantages for these microorganisms. For instance, horizontal surfaces facilitate the deposition of suspended particles from the surrounding liquid, leading to the accumulation of nutrients on the microplastic surfaces. As a result, attached microorganisms have access to these nutrients, promoting their growth and proliferation. Additionally, the attachment to surfaces allows microorganisms to acquire essential metabolites, such as metals, that are adsorbed onto the microplastic surfaces. The formation of biofilms on microplastics, as well as other surfaces, is often facilitated by the secretion of extracellular polymeric substances (EPS) by the microorganisms. Furthermore, the buoyant and persistent nature of microplastics may contribute to the survival and dispersal of pathogens in aquatic environments and soils.
MICROBIAL COMMUNITIES ASSOCIATED WITH MICROPLASTICS
Recent findings have demonstrated that biofilms formed on microplastics exhibit distinct characteristics and lower diversity compared to the microbial communities in the surrounding environment. These microorganisms attached to microplastics have been collectively termed the “plastisphere.” Preliminary investigations suggest that microplastics provide a conducive environment for the survival of microorganisms, even under harsh environmental conditions. Among the bacterial communities associated with microplastics, the phylum Proteobacteria is commonly observed regardless of the type of aquatic environment. In marine settings, Cyanobacteria have also been identified within microplastic biofilms. Furthermore, both freshwater and marine environments have shown the presence of Firmicutes and Proteobacteria within microplastic-associated communities.
Factors Affecting the Microbial Community Attached to Microplastics
The microbial communities attached to microplastics are influenced by various factors, including the plastic material, geographical location, and season. Understanding these factors is crucial for comprehending the dynamics of the “Plastisphere” and its ecological implications.
The microbial composition of the “Plastisphere” can vary based on the geographical location. Studies have shown that bacterial communities on plastic debris differ between ocean basins, such as the North Pacific and North Atlantic subtropical gyres. The location of plastic within the water body also affects the bacterial communities associated with it. Variability in marine plastic bacterial communities has been observed in different locations, including sediment, seawater, and resin pellets sampled on beaches. The surrounding environment, particularly factors like salinity, nutrient levels, temperature, and oxygen content, influences the diversity of bacterial communities in microplastic biofilms. Salinity, in particular, has been identified as a crucial factor affecting bacterial diversity. Low nutrient levels can promote bacterial attachment and biofilm formation, while high nutrient levels may reduce the advantages of biofilm formation. Additionally, water temperature and oxygen levels play important roles in the formation of the “Plastisphere.”The physical characteristics of plastic also impact its colonization by microbial communities. Plastic density is a significant factor in its buoyancy and vertical distribution in the water column. Microplastics with lower density than water tend to float on the surface, potentially being dispersed over long distances. Conversely, microplastics with higher density sink in the water column, distributing attached microorganisms within the bulk water. The hydrophobic surface of plastic and its long half-life make it an attractive substrate for microbial colonization. The large specific surface area of microplastics further enhances the adhesion of microbial cells.
The properties of plastics provide an environment that supports the growth and survival of various microorganisms, including potentially harmful pathogens. Microplastics, with their buoyancy and persistence, have the potential to facilitate the survival and dispersal of pathogens in water and soil, thereby posing health risks. However, the mechanisms underlying the growth and dispersal of pathogenic microorganisms on microplastics remain poorly understood. Another concerning aspect is the relationship between microplastics and antibiotic resistance. Seawater and wastewater have been identified as reservoirs for different antibiotic resistance genes (ARGs) on a global scale. The presence of microplastics in these environments may influence the evolution of microbial communities and contribute to increased gene exchange through the formation of biofilms. Plastic biofilms, with their higher nutrient availability and high cell density, are considered “hot-spots” for horizontal gene transfer (HGT).The combination of microplastics and biofilms creates an environment conducive to the spread of antibiotic resistance, potentially leading to the dissemination of resistant bacteria and ARGs. This scenario has implications for public health and the effectiveness of antibiotics in clinical and environmental settings.
Further research is needed to better understand the interplay between microplastics, biofilm formation, and the dissemination of antibiotic resistance. Developing strategies to mitigate the impact of microplastics on microbial communities and reducing the spread of antibiotic resistance in these environments is crucial for safeguarding human and environmental health.
REFERENCES
- Andrady, A. L. (2017). The plastic in microplastics: A review. Marine pollution bulletin, 119(1), 12-22.
- Harrison, J. P., & Osborn, A. M. (2011). Interactions between microorganisms and marine microplastics: a call for research. Marine Technology Society Journal, (2).
- Kaur, K., Reddy, S., Barathe, P., Oak, U., Shriram, V., Kharat, S. S., … & Kumar, V. (2021). Microplastic-associated pathogens and antimicrobial resistance in environment. Chemosphere, 133005.
- Mammo, F. K., Amoah, I. D., Gani, K. M., Pillay, L., Ratha, S. K., Bux, F., & Kumari, S. (2020). Microplastics in the environment: Interactions with microbes and chemical contaminants. Science of The Total Environment, 743, 140518.
