Genome-Centric Metagenomics Insights into the Plastisphere-Driven Natural Degradation Characteristics and Mechanism of Biodegradable Plastics in Aquatic Environments

Biodegradable plastics (BPs) are pervasively available
as alternatives
to traditional plastics, but their natural degradation characteristics
and microbial-driven degradation mechanisms are poorly understood,
especially in aquatic environments, the primary sink of plastic debris.
Herein, the three-month dynamic degradation process of BPs (the copolymer
of poly(butylene adipate-co-terephthalate) and polylactic
acid (PLA) (PBAT/PLA) and single PLA) in a natural aquatic environment
was investigated, with nonbiodegradable plastics polyvinyl chloride,
polypropylene, and polystyrene as controls. PBAT/PLA showed the weight
loss of 47.4% at 50 days and severe fragmentation within two months,
but no significant decay for other plastics. The significant increase
in the specific surface area and roughness and the weakening of hydrophobicity
within the first month promoted microbial attachment to the PBAT/PLA
surface. Then, a complete microbial succession occurred, including
biofilm formation, maturation, and dispersion. Metagenomic analysis
indicated that plastispheres selectively enriched degraders. Based
on the functional genes involved in BPs degradation, a total of 16
high-quality metagenome-assembled genomes of degraders (mainly Burkholderiaceae)
were recovered from the PBAT/PLA plastisphere. These microbes showed
the greatest degrading potential at the biofilm maturation stage and
executed the functions by PLA_depolymerase, polyesterase, hydrolase,
and esterase. These findings will enhance understanding of BPs’
environmental behavior and microbial roles on plastic degradation.