In modern Western societies, the yeast Candida albicans is frequently found as a commensal member of the gut microbiota, which serves as a reservoir for severe infections. The human gut microbiota has changed significantly due to industrialization. Interestingly, a microbiome study of a mostly isolated, non-Western human population found little indications of C. albicans colonization. Furthermore, C. albicans strains from potential environmental reservoirs are still rarely found and little researched.
We aim to understand the evolution of C. albicans as it adapted to the human host and what effect the changes in human lifestyle had during industrialization and the advent of modern medicine on this member of the human microbiome.
Over 30 strains from the environment, isolated human populations, and animals were examined to elucidate the changes C. albicans has undergone during its co-evolution with modern humans. This included metabolic, genomic, antifungal sensitivity, and virulence tests. Laboratory evolutionary experiments explored how C. albicans adapted to conditions in the modern Western gut.
We found differences between human-derived and environmental strains, with the former showing greater virulence potential as measured in vitro damage to epithelial cells. Some of these human commensal isolates were even more damaging than clinical isolates. In general, the metabolic spectrum of environmental strains was narrower than that of human-derived strains, especially for sugars. Importantly, several non-clinical strains showed resistance to typical antifungal agents. We continuously cultured non-human adapted strains in media containing different dietary sugars for months. The resulting human-adapted strains were specialized to grow better on the dietary sugar provided, but worse on other sugars. A genome-level comparison of the metabolic pathways of the adapted strains, their environmental progenitors, and human isolates is underway.
Our findings highlight substantial differences in metabolism and virulence between human-derived and environmental C. albicans strains. An evolutionary trade-off in adapting to sugars typical of the human diet seems evident.