Biodegradation of vulcanized waste tire rubber by Gordonia polyisoprenivorans Kd2: mechanistic insights and ecological context from indigenous rubber-degrading communities.

Waste tires pose a persistent environmental challenge and resist natural degradation due to vulcanization-induced sulfur crosslinks and the presence of toxic additives, severely limiting microbial accessibility. Gordonia polyisoprenivorans Kd2 was selected as a model organism to study biodegradation potential against ground tire rubber (GTR) of two size fractions (400-600 µm and 3-4 mm) over 28 days in mineral salts medium. GTR samples were comprehensively characterized using ATR-FTIR, FESEM-EDS, CHNS analysis, thermogravimetric analysis (TGA), and solvent swelling-based analysis. In addition, 16S rRNA amplicon profiling was performed to investigate indigenous microbial communities at waste tire dumping sites. Smaller particles supported degradation more effectively than larger fractions, yielding a 2.49 × 103-fold increase in viable cell counts and a maximum weight loss of 5.80%, compared to 1.40% in untreated GTR. Elemental analyses revealed surface oxidation and partial reductions in sulfur and zinc contents. The crosslink density decreased by 10.54% (9.58 × 10-3 to 8.57 × 10-3 mol cm-3) and the sol fraction increased from 2.73% to 5.51%, with Horikx analysis indicating a random main-chain scission mechanism. 16S rRNA amplicon profiling showed an Actinomycetota-dominated community (42.9-44.6%), with Nocardia as the most abundant genus and Gordonia present as a member, indicating that Gordonia operates within a rubber-degrading microbial community, isolated from the soil of rubber tire dumping sites, suggesting the design of synergistic microbial consortia for effective waste tire valorization.