Breaking the bad: Bacillus blocks fungal virulence factors.

François L Mayer,James W Kronstad

doi:10.15698/mic2017.11.599

Abstract

Fungal pathogens rely on the production of specific virulence factors during infection. Inhibiting such factors generally results in reduced fungal pathogenicity. Most studies in the past have focused on understanding the molecular mechanisms of fungal virulence factor expression during mono-culture, or during interaction with the host. However, a potentially important, second type of interaction has been less well studied thus far - the interplay of fungal pathogens of humans with other microbes found in their natural habitat. Specifically, whether environmental bacteria may impact fungal virulence factor production is largely unknown. In our recent work, we have identified the soil bacterium, Bacillus safensis, as a potent inhibitor of virulence factor production by two major fungal pathogens of humans, Cryptococcus neoformans, and Candida albicans. We determined that the anti-virulence factor mechanism is, at least in part, based on production of bacterial chitinases that target and destabilize the fungal cell surface. These findings describe a cross-kingdom interaction between an environmental bacterium and pathogenic fungi, and highlight the fungal cell wall as an attractive antifungal drug target.

Highlights

Fungal pathogens pose a largely under-appreciated threat to human health
We have identified the soil bacterium, Bacillus safensis, as a potent inhibitor of virulence factor production by two major fungal pathogens of humans, Cryptococcus neoformans, and Candida albicans
The polysaccharide capsule is associated with the fungal cell surface; it is assembled onto the α-1,3-glucan layer of the fungal cell wall

Summary

Introduction

Fungal pathogens pose a largely under-appreciated threat to human health. The AIDS-associated, pathogenic fungus C. neoformans, for example, causes ~223,000 new infections each year with a mortality rate exceeding 80%. Fungal pathogens rely on the production of specific virulence factors during infection. We have identified the soil bacterium, Bacillus safensis, as a potent inhibitor of virulence factor production by two major fungal pathogens of humans, Cryptococcus neoformans, and Candida albicans.

Results

Conclusion