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

Abstract

As one of the main pathogens of periodontitis, Porphyromonas gingivalis often forms mixed biofilms with other bacteria or fungi under the gingiva, such as Candida albicans. Heme is an important iron source for P. gingivalis and C. albicans 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 P. gingivalis during the interaction between P. gingivalis and C. albicans. Porphyromonas gingivalis single-species biofilm and P. gingivalis-C. albicans dual-species biofilm were established in a low- and high-heme environment. The results showed that the vitality of P. gingivalis 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 P. gingivalis were observed by electron microscope, and the resistance of P. gingivalis in dual-species biofilm was stronger against the killing effect of healthy human serum and antibiotics. The ability of P. gingivalis 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 P. gingivalis. Gene level analysis showed that P. gingivalis 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 P. gingivalis. In conclusion, our results indicated that the pathogenic potential of P. gingivalis was enhanced by C. albicans through heme competition, which ultimately promoted the occurrence and development of periodontitis and, therefore, C. albicans subgingival colonization should be considered as a factor in assessing the risk of periodontitis.

Porphyromonas gingivalis HmuY and Bacteroides vulgatus Bvu—A Novel Competitive Heme Acquisition Strategy

“…We also demonstrated that HmuY is important for bacterial survival and the invasion of human cells [ 20 ]. Significantly higher HmuY expression in P. gingivalis grown in the form of biofilm together with Candida albicans [ 30 ] and in patients with periodontitis [ 31 , 32 ] confirmed its requirement under in vivo conditions. Recently, we also showed that T. forsythia and P. intermedia produce higher levels of their HmuY homologs when grown under low-iron/heme conditions [ 23 , 24 ].…”

“…Based on these results, one may conclude that heme bound to Bvu might represent a heme reservoir for P. gingivalis and serve as its virulence factor. Other studies showed that competition for heme enhanced the pathogenic potential of P. gingivalis also during its interaction with C. albicans in a mixed biofilm [ 30 ].…”

Recent Advances and Opportunities in the Study of Candida albicans Polymicrobial Biofilms

“…Although the focus of most research regarding the consequence of PMB formation on resistance, has been directed towards antimicrobial resistance, this can be seen as a type of stress resistance and several recent papers have included other types of stress resistance, such as starvation resistance (Gao et al, 2016), resistance to non-antimicrobial drugs, such as nordihydroguaiaretic acid (Fourie et al, 2017), resistance to oxidative stress (Lobo et al, 2019) and serum (Guo et al, 2020). These studies all indicate that not only are PMBs generally more resistant to antimicrobials, but also to a variety of other stresses.…”

In it together: Candida–bacterial oral biofilms and therapeutic strategies

“…In other studies, it showed that virulence factors of P. gingivalis such as cysteine proteases and peptidylarginine deiminase enzymes played a crucial role in C. albicans-P. gingivalis association (Karkowska-Kuleta et al, 2018;Karkowska-Kuleta et al, 2020). As an environmental factor affecting C. albicans-P. gingivalis association, heme, an important iron source for both species, was shown to enhance the pathogenic potential of P. gingivalis while interacting with C. albicans (Guo et al, 2020). Such C. albicans-P. gingivalis association facilitated the invasion and infection of gingival tissue cells (Tamai et al, 2011;Bartnicka et al, 2020), and hampered wound closure (Haverman et al, 2017).…”