Early stage of biofilm formation on bio-based microplastics in a freshwater reservoir

Bio-based plastics (BPs), produced from renewable biomass resources, are currently increasing in terms of products and applications, including high-density polyethylene (HDPE), polylactic acid (PLA), and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). However, their biodegradability and environmental fate is not fully understood, especially in freshwaters. Therefore, we performed an in-situ study in a freshwater reservoir, where we submerged HDPE, PLA and PHBV microscale BPs (mBPs) in dialysis bags to enable exchange of small organic and inorganic molecules including nutrients with the surrounding water. The bacterial biofilm formed on each mBP was characterized by 16S rRNA amplicon sequencing after one and two months. After two months, the Oxalobacteraceae, Pedosphaeraceae, Flavobacteriaceae (Flavobacterium), Chitinophagaceae (Ferruginibacter) increased up to four times and were similarly abundant on all mBPs. The other common members of microbial community also did not display any material preferences. Thus, we looked into the low-abundant bacterial taxa and found that these were significantly diverse on each mBP. Notably, some low-abundant families and genera increased on specific material, for example, Sphingomonadaceae on HDPE, Sphingobacteriaceae on PHBV, Gemmatimonas and Crenorhrix on PLA. To conclude, there was no material preference by common bacterial populations during early stage of biofilm formation on mBPs proved, while the low-abundant bacteria were more diverse and showed certain preferences.