Assimilatory sulfate reduction potential in the plastisphere microbiome is linked to plastic mineralization in...

Microbial communities colonizing plastic surfaces are shaped by environmental factors, yet the role of sulfur in plastisphere assembly and plastic fate remains poorly understood. Here, we collected plastic debris from sulfur-rich, mining-impacted river sediments to characterize plastisphere microbiomes and evaluate their potential roles in plastic transformation. Paenibacillus spp. were identified as core plastisphere members, and their distribution was strongly associated with total sulfur concentrations. Metagenomic binning suggested that Paenibacillus harbored genomic potential associated with plastic transformation/mineralization and sulfate assimilation. An isolate of Paenibacillus provided further laboratory-based evidence that sulfate amendment may support plastic mineralization, although the precise in situ mechanism remains to be clarified. Because both the metagenome-assembled genome and the isolate genome encoded an almost complete assimilatory sulfate reduction pathway but lacked a complete dissimilatory sulfate reduction pathway, the observed sulfate depletion is more conservatively interpreted as sulfate uptake coupled with assimilatory sulfate reduction and subsequent sulfur assimilation into biomass rather than canonical sulfate respiration. Together, these findings suggest that sulfate availability and assimilatory sulfur metabolism may represent underappreciated controls on plastic turnover in sulfur-rich environments by supporting plastic-associated carbon transformation. This study links plastic-carbon fate to local sulfur cycling and provides new insight into microplastic persistence in sulfur-rich aquatic ecosystems.