Commensal Fungi Recapitulate the Protective Benefits of Intestinal Bacteria

Abstract

SUMMARY Commensal intestinal microbes are collectively beneficial in preventing local tissue injury and augmenting systemic antimicrobial immunity. However, given the near-exclusive focus on bacterial species in establishing these protective benefits, the contributions of other types of commensal microbes remain poorly defined. Here we show that commensal fungi can functionally replace intestinal bacteria, by conferring protection against injury to mucosal tissues and positively calibrating the responsiveness of circulating immune cells. Susceptibility to colitis and influenza A virus infection that occur upon commensal bacteria eradication are efficiently overturned by monocolonization with either Candida albicans or Saccharomyces cerevisiae. The protective benefits of commensal fungi are mediated by mannans, a highly conserved component of fungal cell walls, since intestinal stimulation with this moiety alone overrides disease susceptibility in mice depleted of commensal bacteria. Thus, commensal enteric fungi safeguard local and systemic immunity by providing tonic microbial stimulation that can functionally replace intestinal bacteria.

The role of the lung microbiota and the gut-lung axis in respiratory infectious diseases

“…In addition, even if the great majority of the host microbiota is composed of bacteria, recent evidence has demonstrated that fungal or viral agents can also have beneficial functions (Jiang et al, 2017;Kernbauer et al, 2014) and are a natural part of the lung microbiota (Nguyen et al, 2015;Wylie, 2017), indicating that there is a clear need to better study this (somewhat neglected) aspect of the microbiota during health and disease. In addition, even if the great majority of the host microbiota is composed of bacteria, recent evidence has demonstrated that fungal or viral agents can also have beneficial functions (Jiang et al, 2017;Kernbauer et al, 2014) and are a natural part of the lung microbiota (Nguyen et al, 2015;Wylie, 2017), indicating that there is a clear need to better study this (somewhat neglected) aspect of the microbiota during health and disease.…”

Contrasting Strategies: Human Eukaryotic Versus Bacterial Microbiome Research

“…But in mice, C. albicans (not normally a mouse gut colonizer unless mice have received antibiotic treatment) has been interpreted as “protective” and preventive of intestinal diseases and viral infections (Jiang et al. ; Tso et al. ; Wheeler et al.…”

“…Jiang et al. () reveal the “protective” effects of C. albicans and S. cerevisiae , which, argue the authors, occur when these fungi substitute functionally for bacteria that have been depleted in mouse intestines by antibiotics.…”

“…Bacterial microbiome research is just beginning to work with the well‐known idea that pathogenicity is contextual (Table ) rather than the other side of a “fundamental dichotomy” between commensality and pathogenicity (see Jiang et al. , p. 814). In other words, organisms are not by their nature pathogens, but their pathogenic effects are determined by context (e.g.…”

Through the Scope Darkly: The Gut Mycobiome Comes into Focus

“…In mice treated with broad-spectrum antibiotics, monocolonization with Candida albicans or Saccharomyces cerevisiae (not depicted) replaced the protective effect of bacteria against DSS-induced colitis (Jiang et al, 2017). This protective effect required Candida cell wall mannan and host TLR4.…”