Heme Competition Triggers an Increase in the Pathogenic Potential of Porphyromonas gingivalis in Porphyromonas gingivalis-Candida albicans Mixed Biofilm

As one of the main pathogens of periodontitis, often forms mixed biofilms with other bacteria or fungi under the gingiva, such as . Heme is an important iron source for and that supports their growth in the host. From the perspective of heme competition, this study aims to clarify that the competition for heme enhances the pathogenic potential of during the interaction between and . single-species biofilm and - dual-species biofilm were established in a low- and high-heme environment. The results showed that the vitality of was increased in the dual-species biofilm under the condition of low heme, and the same trend was observed under a laser confocal microscope. Furthermore, the morphological changes in were observed by electron microscope, and the resistance of in dual-species biofilm was stronger against the killing effect of healthy human serum and antibiotics. The ability of to agglutinate erythrocyte was also enhanced in dual-species biofilm. These changes disappeared when heme was sufficient, which confirmed that heme competition was the cause of thepathogenicy change in . Gene level analysis showed that was in a superior position in the competition relationship by increasing the expression of heme utilization-related genes, such as HmuY, HmuR, HusA, and Tlr. In addition, the expression of genes encoding gingipains (Kgp, RgpA/B) was also significantly increased. They not only participate in the process of utilizing heme, but also are important components of the virulence factors of . In conclusion, our results indicated that the pathogenic potential of was enhanced by through heme competition, which ultimately promoted the occurrence and development of periodontitis and, therefore, subgingival colonization should be considered as a factor in assessing the risk of periodontitis.