Mycobacteriaceae Mineralizes Micropolyethylene in Riverine Ecosystems

Microplastic
(MP) contamination is a serious global environmental
problem. Plastic contamination has attracted extensive attention during
the past decades. While physiochemical weathering may influence the
properties of MPs, biodegradation by microorganisms could ultimately
mineralize plastics into CO2. Compared to the well-studied
marine ecosystems, the MP biodegradation process in riverine ecosystems,
however, is less understood. The current study focuses on the MP biodegradation
in one of the world’s most plastic contaminated rivers, Pearl
River, using micropolyethylene (mPE) as a model substrate. Mineralization
of 13C-labeled mPE into 13CO2 provided
direct evidence of mPE biodegradation by indigenous microorganisms.
Several Actinobacteriota genera were identified as
putative mPE degraders. Furthermore, two Mycobacteriaceae isolates related to the putative mPE degraders, Mycobacterium sp. mPE3 and Nocardia sp. mPE12, were retrieved,
and their ability to mineralize 13C-mPE into 13CO2 was confirmed. Pangenomic analysis reveals that the
genes related to the proposed mPE biodegradation pathway are shared
by members of Mycobacteriaceae. While both Mycobacterium and Nocardia are known for
their pathogenicity, these populations on the plastisphere in this
study were likely nonpathogenic as they lacked virulence factors.
The current study provided direct evidence for MP mineralization by
indigenous biodegraders and predicted their biodegradation pathway,
which may be harnessed to improve bioremediation of MPs in urban rivers.