# Comparative characterization reveals conserved and divergent ecological traits of oral corynebacteria

## TL;DR

This study explores how different types of oral corynebacteria form biofilms and interact with other microbes, revealing some are key biofilm organizers while others are less specialized.

## Contribution

The study introduces two new corynebacterial strains and reveals conserved and divergent traits in biofilm formation and interspecies communication.

## Key findings

- C. durum strains form thick biofilms with extensive EPS networks, while C. argentoratense forms thinner biofilms with minimal EPS.
- All tested strains secrete extracellular membrane vesicles that induce chain elongation in Streptococcus sanguinis.
- C. argentoratense lacks nitrate reductase genes and cannot grow anaerobically, suggesting a less specialized oral niche.

## Abstract

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, Corynebacterium durum JJ2 and Corynebacterium argentoratense MB1, and compared them with previously characterized and published Corynebacterium durum JJ1 and reference strain Corynebacterium matruchotii ATCC 14266. Phenotypic assays revealed that C. durum strains displayed robust aggregation, thick biofilm formation, and extensive extracellular polymeric substance (EPS) networks, whereas C. argentoratense MB1 and C. matruchotii ATCC 14266 formed thinner biofilms with minimal EPS production. All four strains secreted extracellular membrane vesicles capable of inducing chain elongation in Streptococcus sanguinis, underscoring a conserved interspecies signaling function. Genomic analysis demonstrated close relatedness between C. durum and C. matruchotii, while C. argentoratense 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 C. argentoratense MB1 may represent a less specialized or transient inhabitant of the oral cavity, whereas C. durum and C. matruchotii 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.

Oral 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 Corynebacterium durum and Corynebacterium argentoratense, and comparing them with reference strains including Corynebacterium matruchotii, we provide new insight into their phenotypic diversity, metabolic capacity, and ecological roles. Our results demonstrate that C. durum strains form robust biofilms enriched in extracellular polymeric substances, while C. argentoratense 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 Streptococcus sanguinis, 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.