Bacterial-fungal metabolic interactions within the microbiota and their potential relevance in human health and disease: a short review

Abstract

The composition of the microbiota is the focus of many recent publications describing the effects of the microbiota on host health. In recent years, research has progressed further, investigating not only the diversity of genes and functions but also metabolites produced by microorganisms composing the microbiota of various niches and how these metabolites affect and shape the microbial community. While an abundance of data has been published on bacterial interactions, much less data are available on the interactions of bacteria with another component of the microbiota: the fungal community. Although present in smaller numbers, fungi are essential to the balance of this complex microbial ecosystem. Both bacterial and fungal communities produce metabolites that influence their own population but also that of the other. However, to date, interkingdom interactions occurring through metabolites produced by bacteria and fungi have rarely been described. In this review, we describe the major metabolites produced by both kingdoms and discuss how they influence each other, by what mechanisms and with what consequences for the host.

Keywords: Microbiota; bacteria; disease; fungi; human health; interaction; interkingdom; metabolites.

Figure 1.

Summary of relevant bacterial-fungal metabolic interactions discussed in this review. Bacteria and fungi generally interact through different forms of metabolic crosstalk in the human body. However, some metabolic interactions occur in specific organs and are associated with human health and disease onset. Studies on the bacterial-fungal metabolic interactions in respiratory airways mainly focus on the fungi A. fumigatus and C. albicans, and their distinct relationships with the bacterium P. aeruginosa, although these relationships involve several metabolic pathways.

Figure 2.

The multiplicity of metabolic interactions between P. aeruginosa and C. albicans. Green arrows represent a metabolite-driven enhancement of growth and/or metabolite secretion. Red arrows represent a metabolitedriven inhibition of growth and/or metabolite secretion. Quorum-sensing and alcohol communication pathways cross-interact with each other, as seen with the role played by P. aeruginosa HSL in fungal ethanol-driven stimulation of bacterial trehalose production. Amino acids are hypothetically involved in P. aeruginosa/C. albicans communication; however, this hypothesis has not been studied yet.