(IMAGE) Tokyo Medical and Dental University Caption The structure of the bacterial networks differed between Edo and modern samples, suggesting that the relationships among bacterial species differed between the two sets of samples. Porphyromonas gingivalis, better known as causative bacteria of periodontitis, was a core species in the bacterial network of the modern samples. In contrast, Eubacterium, Mollicutes, and Treponema socranskii might have been important in the bacterial network of the Edo samples. Credit Department of Periodontology, TMDU Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.