Effects of environmental factors on the population dynamics of potential pathogenic bacterial community attached to marine plastic debris.

Marine plastic debris (MPD) harbors potentially pathogenic bacterial communities (PPBs); however, their substrate specificity and environmental influences remain unclear. We aimed to identify the key drivers for the formation of PPB and to elucidate the ecological mechanisms regulating these assemblages. We analyzed MPD samples in South Korea to evaluate PPBs across plastic types, seasons, sampling hot-spot sites, and environmental factors, in comparison to ambient seawater. The bacterial community on the surface of MPD was analyzed using 16S rDNA metabarcoding. The abundance of PPB among the attached bacteria was significantly higher than in the surrounding seawater (PERMANOVA, p < 0.001). PPB on MPD showed significant differences based on water temperature and eutrophication levels (p < 0.001). However, no significant differences were observed among different types of MPD and sampling sites. Vibrio and Pseudoalteromonas were abundant on MPD and included species that infect both marine organisms and humans. Vibrio splendidus and Pseudoalteromonas nigrifaciens thrived under eutrophic conditions below 17 °C. In contrast, Vibrio parahaemolyticus appeared more frequently at temperatures above 17 °C, with lower eutrophic conditions. Therefore, PPB are influenced by environmental factors but exhibit substrate specificity on MPD, indicating that MPD poses a potential risk in facilitating the spread of pathogenic diseases.