No trophy for the trophy? - How lake trophy impacts bacterial assemblages of biofilm on microplastic

The composition of biofilm formed on artificial microplastics (MPs) during the summer stagnation was studied in a field experiment at five lakes with different trophy. After a two-month incubation of MPs, molecular analyses were carried out to isolate the genetic material of bacteria present in the biofilm. Next-generation sequencing of 16S rRNA genes was performed to identify species. Bacterial abundance was also determined in the lake water (2.31 – 4.26 Mcell ml⁻¹) and in the water from experimental baskets containing MPs (0.58 – 4.68 Mcell ml⁻¹). The biofilm formed on the MPs was analysed at various systematic levels, including phylum, family, class, genus, and species. A total of 18 species were identified, with a high percentage of the Proteobacteria phylum noted. This may indicate that this group favours MPs regardless of the trophic level. In this study, the presence of bacteria with the ability to degrade polymers, such as Pseudomonas putida, was observed, as well as Lacibacterium aquatile, which can indicate water quality. Among the other identified bacterial species, several pathogens were found, including Escherichia coli, Staphylococcus aureus, Candidatus Saccharibacteria, and Candidatus Cardinium, which may indicate anthropogenic pollution. The presence of E. coli was detected on MPs in each of the studied lakes, suggesting that MPs may serve as a new vector for dangerous pathogens, regardless of trophic status. Despite the two-month experiment, no statistically significant differences in bacterial species diversity (as measured by alpha and beta indices) were observed between lakes with different trophy.