Growth with Commensal Streptococci Alters Streptococcus mutans Behaviors

Area of Science:

• Microbiology
• Oral Biology
• Genomics

Background:

• Oral bacteria form complex biofilms on tooth surfaces.
• Interactions between bacterial species, such as Streptococcus mutans and commensal streptococci, influence oral homeostasis.
• Previous studies indicated that S. mutans cell-cell signaling is inhibited by other oral streptococci.

Purpose of the Study:

• To investigate the impact of coculturing with oral streptococci on the S. mutans transcriptome and behavior.
• To determine if the observed changes in S. mutans are species-specific or a conserved response.
• To assess the role of upregulated S. mutans genes in interspecies fitness.

Main Methods:

• Whole transcriptome sequencing (RNA-seq) of S. mutans grown alone and in coculture with S. gordonii, S. oralis, S. sanguinis, and a quadculture.
• Microscopy imaging of biofilms.
• Bacteriocin overlay assays.
• Fitness assays for upregulated genes.

Main Results:

• Coculture with oral commensal streptococci induced a conserved, species-independent alteration in the S. mutans transcriptome.
• Microscopy and bacteriocin assays confirmed similar behavioral changes in S. mutans across different commensal species.
• Upregulated genes in S. mutans generally conferred a fitness advantage in mixed-species biofilms, increasing biomass.
• Interactions with non-streptococci species did not yield consistent gene expression profiles.

Conclusions:

• Oral commensal streptococci induce a common, species-independent modification of S. mutans gene expression and behavior.
• These modifications impact S. mutans fitness and biofilm characteristics.
• Understanding multispecies interactions is crucial for comprehending oral microbial community dynamics.