The effect of microplastic on natural transformation and biofilm formation using Acinetobacter baylyi as a model organism

Abstract

Microplastic pollution is a big and rapidly increasing environmental problem in the world. Although the direct effects of microplastic pollution are well-studied the indirect effects are hardly investigated, especially in the context of spreading antibiotic resistance genes. Antibiotic resistance is a natural phenomenon, but the misuse and overuse of antibiotics has led to a rapid development and spread globally, and the result is that antibiotics become ineffective, and infections become more difficult or almost impossible to treat. Antibiotic resistance is now considered as one of the biggest threats to global health, and therefore it is necessary and highly important to investigate and evaluate the impact of microplastics in the aquatic environment. The major aim of this study was to evaluate how the presence of microplastics affects the potential for DNA uptake via natural transformation in the naturally competent bacteria Acinetobacter baylyi, to obtain a better understanding of horizontal gene transfer of antibiotic resistant genes within microplastic-associated communities in the aquatic environment. One important subgoal was to evaluate how DNA uptake via transformation in A. baylyi can be affected by the presence of different concentrations of microplastic polymers, including high density polystyrene (HDPS), high density polyethylene (HDPE), polypropylene (PP), polyvinyl chloride A (PVC A), and polyvinyl chloride B (PVC B). The results obtained in this study revealed that the transformation frequency alters in the presence and absence of different concentrations of polymers. The results indicate small effects, but the trend is clear; the DNA uptake is most efficient in the presence of PP and PVC B. Additional analysis of natural transformation of A. baylyi biofilms grown on microplastics for 96 h, showed that natural transformation on PP was most efficient. The effect of weathering processes on the virgin microplastic surface morphology revealed that weathering processes changes the surface, with an increase in surface roughness, pores and cracks. The early biofilm formation of A. baylyi on the different polymers were found to differ and revealed that most biofilm formation was found on the polymers PVC A, PVC B and PP. Scanning electron microscopic analysis revealed that the bacterial colonization of A. baylyi started in the formed cracks and wells before colonizing smooth surfaces. The results provide new insight into evaluating the risks caused by plastic wastes in the environment, and this study is laying the foundation for further investigations of the interactions between microplastics associated with antibiotic resistant bacteria.