Metabolic Interactions between Bacteria and Fungi in Commensal Oral Biofilms

Abstract

Oral health is more than just the absence of disease. The key to oral health is a diverse microbiome in an ecological balance. The oral microbiota is one of the most complex and diverse microbial communities in the human body. To maintain oral health, balance between the human host and the intrinsic microorganisms is essential. The healthy oral cavity is represented by a great microbial diversity, including both bacteria and fungi. The bacterial microbiome is very well studied. In contrast, fungi inhabiting the oral cavity are often overlooked. All microbial species in the oral cavity form communities which establish a variety of micro-niches and inter- and intra-species interactions. These interactions can be classified into three main groups: physical, chemical and metabolic interactions. Different metabolic interactions are reviewed in this report, among which are the metabolism of sugars, carbon, lactate and oxygen. This review set out with the aim of assessing the importance of metabolic interactions between fungi and bacteria in the healthy oral cavity.

Keywords: bacterium-fungus interactions; healthy oral cavity; oral biofilms; oxygen gradients.

Figure 1

The development of a multi-species biofilm (plaque). (a) Early colonizers bind to the conditioning film (pellicle) (b) The early colonizers start to grow and divide and form microcolonies. The production of EPS starts (c) Co-adhesion of single cells, groups of cells and co-aggregates occur (d) Maturation of the complete plaque (Image taken from: [19] with permission).

Figure 2

Differences in the mycobiota in the oral cavity in health and disease. A dysbiotic state of Candida overgrowth causes epithelial damage. Adapted from [39] with permission.

Figure 3

Example of several interactions in the oral biofilm. Each blue line indicates a physical interaction between different bacteria and fungi. The black arrows indicate the release of metabolic factors by one bacterium which is used by other bacteria. (Aa = Aggregatibacter actinomycetemcomitans). Image taken from: [43] with permission.