Degradation of biomaterials by Streptomyces microflavus DG19: depolymerization activity, genome mining, and soil burial assessment

The accumulation of plastic waste remains a significant environmental challenge despite the alarming evidence and public efforts, emphasizing the need for biodegradable alternatives and appropriate remediation strategies. In this study, Streptomyces microflavus DG19 was evaluated for capacity to degrade a selection of biomaterials that are increasingly penetrating market as readily degradable alternatives. S. microflavus DG19 rapidly degraded poly(3-hydroxybutyrate-co-3-hydroxyvalerate) films in liquid culture (96% weight loss in 7 days) and demonstrated activity against poly(ε-caprolactone) in both agar-based and liquid culture experiments and against cellulose in Congo red assay. 3-Hydroxybutyrate and lactic acid were also metabolized. Genomic analysis identified a number of enzymes involved in carbohydrate and bioplastic degradation. A putative extracellular poly(3-hydroxybutyrate) (PHB) depolymerase (SmPHBase) containing a variant substrate binding domain, and other enzymes involved in 3-hydroxybutyrate metabolism, were of special interest. The presence of > 30 biosynthetic gene clusters highlights this strain’s potential for upcycling bioplastic-containing waste. Soil burial tests demonstrated substantial weight loss in pure biomaterial films and multilayer consumable items containing PHB, showcasing the applicability of S. microflavus DG19 as a composting enhancer. Overall, the findings highlight the pertinence of specialized bacterial strains to biomaterial recycling and upcycling.