Microplastics have received increasing attention worldwide due to their carrier effects. In the aquatic environment, microplastics always show a vertical distribution, which thereby may change the structure and function of the attached microbial communities. However, few studies have focused on this alteration. In this study, the structural changes and functional expression responses of the attached bacterial communities to microplastics under vertical distribution were investigated in the field combined with high-throughput sequencing technology. Polyethylene terephthalate (PET) and polyvinyl chloride (PVC) were selected as the target microplastics, which were frequently detected in the aqueous environment. The results showed that the α-diversity of bacterial communities attached to PET microplastics was much higher than that of those attached to PVC microplastics. The abundance and diversity of the bacterial communities attached to PET and PVC both increased with the increase in water depth. The α-diversity index of bacteria attached to the two typical microplastics was significantly higher in deep water (90 cm) than that in water 30 cm and 60 cm deep. The Cyanobacteria, Proteobacteria, Planctomycetes, and Verrucomicrobia were the dominant phyla in the attached bacterial communities. In addition, the deep water distinctly altered the bacteria community attached to different microplastics. The results of functional prediction showed that the functional expression of pyrimidine metabolism, amino sugar and nucleotide sugar metabolism, starch and sucrose metabolism, and aminoacyl-tRNA biosynthesis were positively correlated with water depth. In addition, the functional responses of the bacterial communities attached to microplastics were also increased, especially in deep water. Further, the bacterial functions of those attached to PET were significantly higher than that of those attached to PVC. This suggests that both the microplastic polymer and the water depth could affect the structure and function of the attached bacterial communities and that the water depth was more important, which may be related to the difference in the vertical distribution of light and turbidity. The results of this study provide a new insight into the microbial response to and environmental risk of microplastic pollution.
Keywords: biofilm; community structure; function; microplastic; vertical distribution.