Molecular basis of the phenotypic variants arising from a mutator.

Bacterial deficiencies in the DNA repair system can produce mutator strains that promote adaptive microevolution. However, the role of mutator strains in marine , capable of generating various gain-of-function genetic variants within biofilms, remains largely unknown. In this study, inactivation of in conferred an approximately 100-fold increased resistance to various antibiotics, including ciprofloxacin, rifampicin and aminoglycoside. Furthermore, the mutator of generated variants that displayed enhanced biofilm formation but reduced swimming motility, indicating a high phenotypic diversity within the Δ population. Additionally, we observed a significant production rate of approximately 50 % for the translucent variants, which play important roles in biofilm formation, when the Δ strain was cultured on agar plates or under shaking conditions. Using whole-genome deep-sequencing combined with genetic manipulation, we demonstrated that point mutations in within the capsular biosynthesis cluster were responsible for the generation of translucent variants in the Δ subpopulation, while mutations in flagellar genes and led to a decrease in swimming motility. Collectively, this study reveals a specific mutator-driven evolution in , characterized by substantial genetic and phenotypic diversification, thereby offering a reservoir of genetic attributes associated with microbial fitness.