Fine-tuned production of hydrogen peroxide promotes biofilm formation of streptococcus parasanguinis by a pathogenic cohabitant Aggregatibacter actinomycetemcomitans

Balanced bacterial biofilm communities help to maintain host health. Disturbance of such balance can lead to bacterial dysbiosis and pathogenesis. However, complex and dynamic bacterial interactions within the biofilm communities are poorly understood. In this study, we used a dual-species biofilm consisting of the periodontal pathogen Aggregatibacter actinomycetemcomitans, and a commensal Streptococcus parasanguinis to investigate bacterial interactions since the two organisms have been found to coexist during the development of localized aggressive periodontal disease. We report that A. actinomycetemcomitans promoted biofilm formation of S. parasanguinis in vitro and in vivo. Protein profiling of S. parasanguinis co-cultured with A. actinomycetemcomitans revealed a significant decrease in the protein level of pyruvate oxidase(PoxL), an enzyme required for the generation of hydrogen peroxide (H₂O₂). Consistently, the H₂O₂ concentration was concurrently decreased. However, the complete removal of H₂O₂ impaired the biofilm formation. H₂O₂ at a low concentration range regulated by A. actinomycetemcomitans enhanced the biofilm formation. These results demonstrate that A. actinomycetemcomitans promotes the S. parasanguinis biofilm formation through modulating the production of H₂O₂ by fine-tuning the expression of poxL, indicating that H₂O₂ functions as a signaling molecule. Taken together, this report revealed a previously unknown bacteria-bacteria interaction mechanism.