Biodegradation of vulcanized rubber by a gut bacterium from plastic-eating mealworms

The disposal of vulcanized rubber waste is difficult due to the presence of three-dimensional crosslinking network structure. Here, we report that a bacterium Acinetobacter sp. BIT-H3, isolated from the gut of plastic -eating mealworm, can grow on and degrade vulcanized poly(cis-1,4-isoprene) rubber (vPR). Scanning elec-tronic microscopy (SEM) shows that strain BIT-H3 can penetrate into the vPR and produce craters and cracks. The tensile strength and the crosslink density of vPR decreased by 53.2% and 29.3% after ten weeks' incubation, respectively. The results of Horikx analysis, attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, and X-ray absorption near-edge structure (XANES) spectroscopy reveal that strain BIT-H3 can break down both sulfide bridges and double bonds of polymeric backbone within vPR. Sulfate and oligo(cis-1,4 isoprene) with terminal aldehyde and keto groups were identified as metabolic products released during vPR degradation. Through genomic and transcriptional analyses, five enzymes of dszA, dszC1, dszC2, Laccase2147, and Peroxidase1232 were found to be responsible for vPR degradation. Based on the chemical structure char-acterizations and molecular analyses, a vPR biodegradation pathway was proposed for strain BIT-H3. These findings pave a way for exploiting vulcanized rubber-degrading microorganisms from insect gut and contribute to establish a biodegradation method for vulcanized rubber waste disposal.

Automated summary

This study reports a bacterium Acinetobacter sp. BIT-H3 isolated from the gut of plastic-eating mealworm, which showed the ability to grow on and degrade vulcanized rubber waste. The bacterium was found to penetrate the rubber and reduce its tensile strength and crosslink density. Genomic and transcriptional analysis revealed five enzymes responsible for the degradation of vulcanized rubber. These findings provide a new approach for the development of biodegradation methods for vulcanized rubber waste disposal, utilizing rubber-degrading microorganisms from insect gut.