Identified <i>Neptunicella plasticusilytica</i> sp. nov. and its novel PET-degrading enzyme derived from mangrove plastic debris

Mangrove ecosystems are critical for coastal protection and biodiversity but are increasingly threatened by plastic pollution, particularly polyethylene terephthalate (PET). In this study, a novel marine bacterium, strain SCSIO 80796^T, was isolated from PET debris collected from the mangrove in QiAo Island, Zhuhai, China. Using a polyphasic taxonomic approach, including 16S rRNA gene sequencing, genome-based comparisons (average nucleotide identity [ANI] 72.2%, digital DNA-DNA hybridization [dDDH] 19.0%, average amino acid identity [AAI] 70.6%), and phenotypic and chemotaxonomic analyses, the strain was classified as a novel species within the genus <i>Neptunicella</i>. It is proposed as <i>Neptunicella plasticusilytica</i> sp. nov. (type strain SCSIO 80796ᵀ = MCCC 1K08369^T = KCTC 92826^T). Genomic analysis revealed that strain SCSIO 80796ᵀ encodes a novel PET-degrading enzyme, <i>Nm</i>Cut, which degrades PET and yields 105-120 µM of degradation products [terephthalic acid (TPA), mono(2-hydroxyethyl) terephthalate (MHET), bis(2-hydroxyethyl) terephthalate (BHET)] within 48 h at 60°C. <i>Nm</i>Cut exhibits both structural and evolutionary novelty, featuring a unique PET-binding module (PBM) absent in known PETases. PBM is characterized by a long, positively charged α-helix enriched in aromatic residues, forming a distinct substrate-interacting surface with potential as a transferable domain to enhance the efficiency of other plastic-degrading enzymes. This study not only expands the known diversity within <i>Neptunicella</i> but also highlights the potential of marine-derived microbes in addressing plastic pollution through biotechnological applications.IMPORTANCEThe discovery of <i>Neptunicella plasticusilytica</i> sp. nov. advances marine microbial ecology by revealing a novel species in the scarcely studied genus <i>Neptunicella</i>, which previously contained only one cultured representative. Isolated from plastic-polluted mangroves, this bacterium exemplifies microbial adaptation to anthropogenic habitats. Its functional uniqueness is underscored by a phylogenetically distinct polyethylene terephthalate (PET)-degrading enzyme (<i>Nm</i>Cut), forming an evolutionary clade separate from all known plastic-degrading enzymes. By integrating taxonomic discovery with functional genomics, this study bridges the gap between microbial diversity and biotechnological potential. The dual novelty of <i>N. plasticusilytica</i>-as a taxonomic addition and a source of evolutionarily unique enzymes-highlights the importance of exploring understudied environments to address global challenges like plastic pollution.