Investigating how microplastics impact bacteriophage infectivity in water-based settings

Polymer-based materials are nearly ubiquitous, reaching even the deepest regions of the oceans, and their global production exceeds recycling, generating massive amounts of microplastic particulate matter water pollution. Small polymer particles not only release these chemicals, but also reduce the number of phages.

Recently, researchers from the Institute of Physical Chemistry, Polish Academy of Sciences, led by Professor Jan Paczysny, explored this area, showing the scale of the problem. In their work, they studied the effects of microplastics on infection of phages in an aquatic environment.

It’s hard to imagine a world without plastic-based products. Synthetic materials are used in every sphere of life, from textiles and food and pharmacy packaging to materials used in the construction industry. It is an indispensable part of life due to its multifunctionality. Plastic is lightweight, easy to mold, resistant to environmental conditions, and cheaper than many other synthetic materials, making it very popular.

However, it is not necessarily friendly to health and the environment, especially as the plastic particles become smaller. Upon reaching water tanks, synthetics can easily be mechanically broken down into smaller pieces. It can also undergo degradation under ultraviolet light, chemical degradation, or even biodegradation, so small plastic particles hang around in water tanks for a very long time. Such microplastics less than 5 mm in diameter or smaller pieces like nanoplastics (even a million times smaller than microplastics) are everywhere, even in tap water or mammalian milk.

When these tiny plastic particles enter the environment, they become a serious problem for water systems such as lakes, rivers, seas, and even oceans, as they slowly decompose, releasing many harmful chemicals. Unfortunately, the list is very long, from plasticizers, dyes, and flame retardants to heavy metal ions that can cause many disorders or diseases. Furthermore, the microplastic surface absorbs organic compounds that act as food storage for microbial biofilms, leading to an imbalance between specific groups of microorganisms that make up the biofilms, including phages.

Here begins the story of science. Recently, Prof. Jan Paczysny’s team from the Institute of Physical Chemistry, Polish Academy of Sciences, demonstrated the effects of different microplastics on different types of phages in aqueous media. In their work, scientists have used twelve different commonly used polymers, for example, polycarbonate (PC), polyethylene (PE), PET, poly(methyl methacrylate) (PMMA), polypropylene (PP), etc., And cut them into small pieces, and use them as sources of all the prepared materials.

“We have wisely selected industrial-grade polymers to reflect true sources of microplastics in the environment,” says the professor. “We prepared the polymer samples by crushing large pieces of commercial plastic. This process mimics how plastic fragments are formed in the environment.” Jan Bakzisny.

Sounds easy, right? In fact, the experiment is more complex to simulate natural environmental conditions. Besides many features affecting the experiment, leachates commonly used as polymer additives play an important role. The researchers found a relationship between the decrease in phages on the microplastic surface and the presence of certain leachates.

Interestingly, the decrease in the number of phages on the microplastic surface could be subject to two different mechanisms. The first relates to the presence of liquid substances that can inactivate up to 50% of phages. The second is related to specific sizes of polymer materials, where the generation of nanoparticles and submicrons plays a major role and adsorption leads to the removal of phages.

“The effect of filtrate was measured when the phages were exposed not to the particles themselves but to the insulator pre-incubated with microplastics,” says Prof. Bakzisny. “A double overlaid plate counting method was used to assess the phage titer. We used a classical linear regression model to investigate the physical and chemical parameters (tested 65 variables) that govern low phage titer”.

The research study focuses on the relationship between the number of phages and the physical and chemical properties of microplastics as an introduction to the broad field of ecotoxicological studies. As it is only the case every day, phages end up to 40% of the bacterial biomass, they play a vital role in maintaining balance in the bacterial community in all environments, from the Big Blue to sewage. Once the microplastic enters the environment, its surface hosts the biofilm layer, which serves as a colonization booster for microorganisms, and therein lies the problem.

Many bacterial strains, which are transmitted through microplastics, can colonize uncontrollably. As an effect, they can affect the ecosystems in some aquatic areas without controlling the phages, affecting not only animals but also humans. What does that mean practically? Let’s take a look at seafood. Microplastics reach the digestive tracts of fish and other animals, disturbing organisms in the gut as well as forming aggregates in other tissues. Therefore, when we consume them, these microplastics enter our digestive system, and as these polymer pieces decrease in size, they can also collect in the body, which can lead to serious health problems. It sounds scary, but from the findings of scientists from the IPC PAS it is clear that the increasing pollution of the environment with microplastics can have a significant impact on global ecosystems.

Work on the effect of microplastics on phages has been published in Journal of Environmental Quality.