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.