Longitudinal gut mycobiota changes in Japanese infants during first three years of life

Although fungi can have a large impact on host health through the stimulation of the immune system and toxin production, few studies have investigated the gut mycobiota during infancy, a period during which sensitivity to internal and external stimuli is high. To capture the trend in fungal colonization during infancy, we evaluated the gut mycobiota of ten Japanese infants during the first 3 years of life. Infants had two major phyla, Ascomycota (68.9%) and Basidiomycota (29.6%), and the most abundant genus was Saccharomyces (26.8%), followed by Malassezia (18.5%), Candida (12.3%), Meyerozyma (8.5%), and Penicillium (8.3%). Alpha diversity analysis revealed a significant decrease in fungal richness and evenness with age, suggesting adaptive selection of the colonizing species in the gut environment. Beta diversity analysis divided infant mycobiota into age-related clusters and showed discrete separation before and after weaning, suggesting shift in microenvironment via weaning. In the initial stage, a variety of fungal species that likely originated from an environment, such as Malassezia spp., was highly colonized and were replaced by yeasts, such as Saccharomyces, after weaning. Further studies are needed to shed light on how the passage of the series of fungal colonizations in infancy affects the development of the host immune system and the other homeostasis involved in health later in life.