Comparative characterization reveals conserved and divergent ecological traits of oral corynebacteria

Corynebacteria are abundant members of the oral microbiome and increasingly recognized as key structural organizers of supragingival biofilms. Despite their prevalence, the ecological roles and phenotypic traits of many oral corynebacterial species remain poorly defined. Here, we isolated and characterized two new strains, <i>Corynebacterium durum</i> JJ2 and <i>Corynebacterium argentoratense</i> MB1, and compared them with previously characterized and published <i>Corynebacterium durum</i> JJ1 and reference strain <i>Corynebacterium matruchotii</i> ATCC 14266. Phenotypic assays revealed that <i>C. durum</i> strains displayed robust aggregation, thick biofilm formation, and extensive extracellular polymeric substance (EPS) networks, whereas <i>C. argentoratense</i> MB1 and <i>C. matruchotii</i> ATCC 14266 formed thinner biofilms with minimal EPS production. All four strains secreted extracellular membrane vesicles capable of inducing chain elongation in <i>Streptococcus sanguinis</i>, underscoring a conserved interspecies signaling function. Genomic analysis demonstrated close relatedness between <i>C. durum</i> and <i>C. matruchotii</i>, while <i>C. argentoratense</i> MB1 was more distantly related, with a reduced genome, fewer metabolic pathways, and the absence of nitrate reductase genes, consistent with its inability to grow under anaerobic conditions. These findings suggest that <i>C. argentoratense</i> MB1 may represent a less specialized or transient inhabitant of the oral cavity, whereas <i>C. durum</i> and <i>C. matruchotii</i> are well adapted to the oral niche. Together, this study expands our understanding of phenotypic diversity, metabolic capacity, and interspecies interactions among selected oral corynebacteria, highlighting their potential importance as biofilm organizers and contributors to oral microbial ecology.IMPORTANCEOral corynebacteria contribute to the structural and ecological stability of supragingival communities. Yet, their species-level functions remain poorly defined. By isolating and characterizing new strains of <i>Corynebacterium durum</i> and <i>Corynebacterium argentoratense</i>, and comparing them with reference strains including <i>Corynebacterium matruchotii</i>, we provide new insight into their phenotypic diversity, metabolic capacity, and ecological roles. Our results demonstrate that <i>C. durum</i> strains form robust biofilms enriched in extracellular polymeric substances, while <i>C. argentoratense</i> produces thinner biofilms and lacks the genomic features required for anaerobic growth, suggesting a less specialized or transient role in the oral cavity. Importantly, we show that extracellular membrane vesicles secreted by all tested strains promote chain elongation in <i>Streptococcus sanguinis</i>, highlighting a conserved mechanism of interspecies communication. These findings advance our understanding of how oral corynebacteria contribute to biofilm organization and microbial homeostasis and position them as critical but understudied players in oral microbial ecology.