PHA Microplastic Aging Decreases N<sub>2</sub>O Sink Capacity: Released γ-Butyrolactone Decouples Denitrifying Electron Transfer and Oxidative Phosphorylation
Yu Zhang, Jing Lu, Xiao-Zheng Zhang, Zheng-Zhe Zhang, Ren‐Cun Jin
Abstract
Bacterial denitrification is a main pathway for soil N 2 O sinks, which is crucial for assessing and controlling N 2 O emissions. Biobased polyhydroxyalkanoate (PHA) microplastic particles (MPs) degrade slowly in conventional environments, remaining inert for extended periods. However, the impacts of PHA microplastic aging on the bacterial N 2 O sink capacity before degradation remain poorly understood. Here, the soil model strain Paracoccus denitrificans was exposed to 0.05–0.5% (w/w) virgin and aged PHA MPs. Although no significant changes in the molecular weights were observed, aged PHA MPs hindered cell growth and N 2 O reduction rates, leading to a surge in N 2 O emissions. 1 H NMR spectroscopy and UPLC-QTOF-MS analysis identified γ-butyrolactone as the key component released from aged PHA MPs. Metabolic verifications at the cellular level confirmed its inhibition on the N 2 O sink and ATP synthesis. The γ-butyrolactone that protonated and hydrolyzed spontaneously in the periplasm would compete for protons with ATPase and destroy the coupling between denitrifying electron transfer and oxidative phosphorylation. Consequently, energy-deficient cells reduced the electron supply for N 2 O reduction, which did not contribute to energy conservation. This work unveils a novel mechanism by which PHA microplastic aging impairs the bacterial N 2 O sink and highlights the need to consider environmental risks posed by biobased microplastic aging.