Substrate-specific bacterial and fungal communities in the Jukskei River plastisphere revealed by full-length amplicon sequencing

The escalating crisis of plastic pollution in aquatic ecosystems has created a novel ecological niche known as the plastisphere, where microbial communities colonize plastic surfaces, influencing biogeochemical cycles, pollutant degradation, and ecosystem health. Despite global plastisphere research, studies in subtropical, eutrophic African urban rivers remain scarce, limiting insights into substrate-specific microbial assembly and bioremediation potential in polluted freshwater systems. Plastic debris in the Jukskei River, an urban waterway in Johannesburg, South Africa, hosts distinct bacterial and fungal communities on polyethylene (PE) and polystyrene (PS) surfaces. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy revealed oxidative weathering (carbonyl indices 0.08–0.28) consistent with environmental aging. Targeted amplicon sequencing (full-length 16S rRNA and ITS regions via PacBio HiFi) demonstrated substrate-specific community composition (PERMANOVA, pseudo-F{1,8} = 3.45, R 2 = 0.40, p < 0.01), with PE supporting higher genus-level evenness and taxa such as Romboutsia , Cutibacterium , and Sphingomonas , while PS was characterized by greater representation of Lactococcus, Clostridium sensu stricto, and lactic acid bacteria. Low-abundance potential pathogens at the genus level ( Escherichia-Shigella , Streptococcus ) showed statistically significant correlations with eutrophication indicators (BOD₅, nitrate) and cadmium, although no causal mechanisms were established. Additionally, the amplicon-based approach used was unable to confirm both species-level resolution and virulence potential. PICRUSt2 and FUNGuild predictions indicated the presence of broadly distributed metabolic pathways and guilds, but these inferences do not constitute evidence of active plastic biodegradation or specialized ecological roles. This study provides the first amplicon-based characterization of the plastisphere in a polluted African urban river, revealing substrate-driven bacterial assembly patterns and highlighting the need for future functional validation to assess bioremediation potential and public health risks.