Heteroaggregation of virions and microplastics reduces the number of active bacteriophages in aqueous environments

National Science Centre, Poland, within PRELUDIUM BIS grant 2020/39/O/ST5/01017 National Science Centre, Poland, within SONATA BIS grant 2017/26/E/ST4/00041

The objective of this study is to explore the effects of microplastics on the viability of the bacteriophages in an aqueous environment. Bacteriophages (phages), i.e., viruses of bacteria, are essential in homeostasis. It is estimated that phages cause up to 40% of the death of all bacteria daily. Any factor affecting phage activity is vital for the whole food chain and the ecology of numerous niches. We hypothesize that the number of active phages decreases due to the virions’ adsorption on microplastic particles or by the released leachables from additives used in the production of plastic, e.g., stabilizers, plasticizers, colorants, and reinforcements. We exposed three diverse phages, namely T4 (tailed), MS2 (icosahedral), and M13 (filamentous), to 1 mg/mL suspension of twelve industrial grade plastics [acrylonitrile butadiene styrene (ABS), high-impact polystyrene (HIPS), poly-ε-caproamide (PA6), polycarbonate (PC), polyethylene (PE), polyethylene terephthalate (PET), poly(methyl methacrylate) (PMMA), polypropylene (PP), polystyrene (PS), polytetrafluoroethylene (PTFE), polyurethane (PUR), polyvinyl chloride (PVC)] shredded to obtain microparticles of radius ranging from 2 to 50 µm. The effect of leachables was measured upon exposure of phages not to particles themselves but to the buffer pre-incubated with microplastics. A double-overlay plaque counting method was used to assess phage titers. We employed a classical linear regression model to verify which physicochemical parameters (65 variables were tested) govern the decrease of phage titers. The key finding is that adsorption mechanisms result in up to complete scavenging of virions, whereas leachables deactivate up to 50% of phages. This study reveals microplastic pollution’s plausible and unforeseen ecotoxicological effect causing phage deactivation. Also, phage transmission through adsorption can alter the balance of the food chain in the new environment. The effect depends mainly on the zeta potentials of the polymers and the phage type.