The Indoor Mycobiomes of Daycare Centers Are Affected by Occupancy and Climate

Abstract

Many children spend considerable time in daycare centers and may here be influenced by indoor microorganisms, including fungi. In this study, we investigate the indoor mycobiome of 125 daycare centers distributed along strong environmental gradients throughout Norway. Dust samples were collected from doorframes outside and inside buildings using a community science sampling approach. Fungal communities in the dust samples were analyzed using DNA metabarcoding of the ITS2 region. We observed a marked difference between the outdoor and indoor mycobiomes. The indoor mycobiome included considerably more yeasts and molds compared to the outdoor samples, with Saccharomyces, Mucor, Malassezia and Penicillium among the most dominant fungal genera. Changes in the indoor fungal richness and composition correlated to numerous variables related to both outdoor and indoor conditions; there was a clear geographic structure in the indoor mycobiome composition that mirrored the outdoor climate, ranging from humid areas in western Norway to drier and colder areas in eastern Norway. Moreover, the number of children in the daycare centers, as well as various building features, influenced the indoor mycobiome composition. We conclude that the indoor mycobiome in Norwegian daycare centers is structured by multiple factors and is dominated by yeasts and molds. This study exemplifies how community science sampling enables DNA-based analyses of a high number of samples covering wide geographic areas. Importance With an alarming increase in chronic diseases like childhood asthma and allergies, there is an increased focus on the exposure of young children to indoor biological and chemical air pollutants. Our study of 125 daycares throughout Norway demonstrates that the indoor mycobiome not only reflects co-occurring outdoor fungi but includes a high abundance of yeast and mold fungi with an affinity for indoor environments. A multitude of factors influence the indoor mycobiome in daycares, including building type, inhabitants, as well as the outdoor environment. Many of the detected yeasts and molds are likely associated with the human body, where some have been coupled to allergies and respiratory problems. Our results call for further studies investigating the potential impact of the identified daycare-associated mycobiomes on children health.

Comparison of Methods to Identify and Monitor Mold Damages in Buildings

“…Two of them are the limited accuracy of incomplete reference sequence databases and the insufficient intraspecific sequence variation in barcodes (including ITS1 and ITS2) to resolve the taxonomy at the species level, as discussed above for some common mold genera, such as Penicillium, Cladosporium, Aspegillus, and Alternaria. In this study, the percentages of non-identified OTUs were similar to those observed in other DNA metabarcoding studies [22,23], increasing considerably from the phylum (4.5%) to order (10.8%), genus (28.5%), and species (47.7%) levels. Therefore, the identity and ecology of a significant proportion of the fungi detected by DNA sequencing remain unknown.…”

“…In building ecology, a challenging task is to differentiate between moisture-damage indicator fungi that can colonize building materials, and grow under indoor conditions, from those widespread airborne fungi more related to outdoor air, vegetation, and the household food [13], whose distribution indoors is largely driven by stochastic processes. Previous studies have demonstrated that the indoor dust mycobiota is mainly composed of spores and hyphal fragments coming from both outdoor and indoor sources [22,23,[35][36][37]. Our study has also reflected this dual origin of the dust fungi.…”

“…The ecology of the genera Cladosporium and Saccharomyces is very diverse, being widely distributed in both outdoor (e.g., soil and phyllosphere) and indoor environments. However, previous studies on dust have demonstrated that the proportion of Cladosporium is often higher in outdoor samples, while Saccharomyces is higher in indoor samples [22,23,35]. These multiple inputs led to a high fungal diversity in the dust samples, which showed a much higher richness than the mold samples.…”

“…Our study has also reflected this dual origin of the dust fungi. Taxa clearly related to the outdoor environment, such as the plant-associated Thekopsora and Fomitopsis, were found, as well as taxa that can be related to secondary indoor sources: Saccharomyces, which is often found in the occupants' skin [23], or Chaetomium, Aspergillus, and Serpula which can grow and produce millions of spores on different damaged materials [11]. The ecology of the genera Cladosporium and Saccharomyces is very diverse, being widely distributed in both outdoor (e.g., soil and phyllosphere) and indoor environments.…”

“…DNA metabarcoding, based on the highthroughput sequencing of an amplified DNA marker, has become a key tool for surveying environmental microbial communities in the last decades. In several studies, the mycobiota of the built environment have been surveyed through DNA metabarcoding analyses of the internal transcribed spacer (ITS) of the nuclear rRNA operon [20][21][22][23]. However, DNA analyses are not able to distinguish between live and dead fungi or identify specifically those that are capable of growing on building materials.…”