Characterization of polystyrene-attached bacteria isolated by enrichment culture of estuarine sediments with polystyrene pellets

We evaluated fundamental characteristics of bacteria attached onto microplastics (MPs) in aquatic environments. Twenty-four strains were isolated from the estuarine sediments in Tokyo Bay by enrichment culture using polystyrene (PS) pellets and were found to belong to various genera, one of which was identified as an opportunistic pathogen, Brevundimonas diminuta. The ability of most of them to form biofilm on PS was high, and the PS-attached strains were selected based on the phylogenetic diversity to examine characteristics such as antibacterial susceptibility, enzymatic activity, and degradation ability of high-molecular-weight compounds. Antibacterial susceptibility tests using thirteen antibacterial compounds showed that all the selected strains were susceptible to tetracycline, but none of them were susceptible to kanamycin. All the strains were also susceptible to several antibacterial compounds on the basis of different mechanisms of action. Concerns have been raised over the pathogenic and/or antibiotic-resistant bacteria enriched on MPs in studies using high-throughput sequencing analysis; however, this study suggests that relationships between MPs and pathogenic and antibiotic-resistant bacteria should be continuously considered as ecological risk, which may be limited. In addition, PS-attached bacteria showed several activities, as shown by the results of enzymatic activity and hydrolysis of high-molecular-weight compounds, and were diverse biochemically.