Background/Question/Methods Microplastics (plastic debris with diameter <5mm) are of particular concern to the environment. However, there is a scarcity of information concerning the effects of conditioning films on bacterial colonization of microplastics in freshwater ecosystems. The formation of conditioning films on substrate surfaces is a critical step in the priming of substrates for bacterial colonization in aquatic systems. Conditioning films are comprised of dissolved organic solutes that are deposited on to surfaces of substrates, which attract bacterial colonizers. Moreover, the thicknesses of conditioning films are influenced by the physicochemical properties of substrate surfaces. This study aimed to understand the effects of different conditioning films on bacterial colonization of microplastic surfaces in freshwater. Five types of conditioning films were analyzed: Bovine Serum Albumin (BSA), sodium alginate (medium and very low viscosity), humic and fulvic acid; all are components of biofilms on four types of microplastic disks (diameter <5mm): polypropylene (PP), polystyrene (PS), high-density polyethylene (HDPE), and low-density polyethylene (LDPE). All plastic disks were placed in respective microcosms after incubation with individual conditioning films for 20 minutes. Microcosms consisted of Fraquil over a period of 72 hours and sampled at 48- and 72-hours. The disks were analyzed for conditioning film thicknesses using AFM (atomic force microscopy) and 16S rRNA sequencing to determine compositions of bacterial communities in the presence of different conditioning films. Results/Conclusions Bacterial community compositions changed over time based on the type of conditioning films and type of microplastic surface being colonized. Conditioning film thicknesses also varied on microplastic surfaces after AFM analyses. Based on plastic types and the type of aquatic environment, conditioning film deposition can vary according to microplastic substrate types. Based on conditioning film types and microplastic types, bacterial community colonization is also affected. Subsequent research will focus on identifying the effects of varying conditioning film thicknesses on bacterial community colonization. Moreover, this current research project raises questions about the roles of conditioning films on microplastic sedimentation in freshwater. Understanding these questions will provide insights on the fates of microplastic debris in freshwater.
