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Impact of Plasticizers on the Microbial Degradation of Polyhydroxybutyrate (PHB)
Summary
PHB depolymerase gene expression and microbial degradation rates of polyhydroxybutyrate (PHB) were unaffected by the presence of phthalate ester- and glycol-based plasticizers, with over 98% of PHB degraded within 48 hours in liquid media. This confirms that plasticized PHB retains its biodegradability, supporting its viability as a drop-in replacement for conventional plastics that persist as microplastic pollutants in the environment.
Polyhydroxybutyrate (PHB) is a biodegradable polyester considered a sustainable alternative to petroleum-based plastics. However, its biodegradation in the presence of plasticizers remains poorly defined. This study investigated the impact of phthalate ester- and glycol-based plasticizers on PHB degradation by Ralstonia sp. C1. Real Time -Polymerase Chain Reaction(RT-PCR) analysis showed that expression of the PHB depolymerase gene phaZa1 remained unchanged in all additive-treated cultures, indicating no transcriptional interference. Liquid-medium degradation assays quantified by HPLC revealed rapid PHB utilization, with more than 50% degraded within 24 h and over 98% degraded within 48 h, with no significant differences relative to the control. Growth-inhibition assays further demonstrated that none of the plasticizers impaired bacterial viability, as OD600 profiles were comparable to untreated cultures. Soil degradation experiments confirmed that PHB films containing additives decomposed at rates similar to additive-free films, reaching approximately 80% degradation within 10 weeks. Overall, the tested plasticizers did not affect enzyme expression, microbial activity, or PHB biodegradation, highlighting the suitability of plasticized PHB materials for environmentally sustainable applications and supporting their scalable use as biodegradable alternatives to conventional plastics.