Abstract: The functional components of bioflocs are highly complex microbial aggregates, and the design and optimization of these intricate microbial communities are crucial for improving biofloc performance. To screen self-flocculating bacteria as exogenous reinforcement strains for biofloc systems, a self-flocculating strain was isolated and purified from the breeding pond of Chinese grass turtles. Its taxonomic status was identified through polyphasic taxonomy, which included 16S rRNA gene sequencing, phylogeneticanalysis, and whole genome sequence analyses. Strain W12showed the highest similarity with Massilia arenosa MC02^T at 96.21%, the ANI values for strain W12 ranged from 71.61%—72.23%, and the dDDH values ranged from 19.6%—22.9% with several type strains of closely related species, which were much lower than the thresholds for discriminating a new bacteria species. This strongly indicates that W12 is a novel species within the genus Massilia. In addition, genome-wide analysis reveales that the self-flocculation mechanism of W12 may is similar to that of the Zoogloea resiniphila, likely mediated by a combination of extracellular polysaccharides and PEP-CTERM proteins. It is hypothesized that strain W12synthesizes PHB through the PHB synthesis pathway I, involving three enzymes: PhaA, PhaB, and PhaC. The discovery of strain W12, a novel species of the genus Massilia isolated from a turtle breeding pond, highlights its ability to synthesize PHB and self-flocculation through extracellular polysaccharides and PEP-CTERM proteins. These properties are significant for bioflocs formation, underscoring the potential application of strains in enhancing the biofloc system.