Biodegradation of Polypropylene in Presence of Chromium Mediated by Stenotrophomonas sp. and Lysinibacillus sp. Isolated from Wetland Sediments

Plastics and heavy metals are deeply integrated into daily life, and their production and consumption contribute to waste generation and environmental contamination. In this study, native microorganisms from wetland sediments of the Paraná Delta, Argentina, were used to evaluate the simultaneous bioremediation of chromium and polypropylene. A total of 73 isolates were obtained from sediments contaminated with both heavy metals and microplastics using enrichment culture media. These isolates were characterized based on their metabolic properties through biochemical tests. Redundant isolates and those exhibiting signs of pathogenicity were discarded. From the remaining 51 isolates, a selection was made based on their biofilm-forming capacity, polypropylene biodegradation potential, and chromium resistance. These microorganisms were identified by sequencing the 16S rRNA region. The results showed that bacteria belonging to Stenotrophomonas sp. reduced the total polypropylene degradation time by more than 100-fold. Additionally, microbial activity led to detectable changes in the polypropylene surface and structure, as evidenced by modifications in surface morphology and FTIR spectra in the inoculated treatments. In the presence of 5 ppm Cr(VI), Lysinibacillus sp. achieved better results, reducing the degradation time by over 10-fold compared to the uninoculated treatment and demonstrating an enhanced ability to form biofilms under these conditions. At the same time, some removal of Cr(VI) (around 8%) was observed. On the other hand, Stenotrophomonas sp. reduced the degradation time 7-fold compared to the uninoculated treatment under these conditions. This is the first time that Stenotrophomonas sp. and Lysinibacillus sp. are reported to degrade polypropylene in the presence of other contaminants.