Abstract
In modern urban environments children have a high incidence of inflammatory disorders, including allergies, asthma, and type1 diabetes. The underlying cause of these disorders, according to the biodiversity hypothesis, is an imbalance in immune regulation caused by a weak interaction with environmental microbes. In this 2-year study, we analyzed bacterial community shifts in the soil surface in day-care centers and commensal bacteria inhabiting the mouth, skin, and gut of children. We compared two different day-care environments: standard urban day-care centers and intervention day-care centers. Yards in the latter were amended with biodiverse forest floor vegetation and sod at the beginning of the study. Intervention caused a long-standing increase in the relative abundance of nonpathogenic environmental mycobacteria in the surface soils. Treatment-specific shifts became evident in the community composition of Gammaproteobacteria, Negativicutes, and Bacilli, which jointly accounted for almost 40 and 50% of the taxa on the intervention day-care children's skin and in saliva, respectively. In the year-one skin swabs, richness of Alpha-, Beta-, and Gammaproteobacteria was higher, and the relative abundance of potentially pathogenic bacteria, including Haemophilus parainfluenzae, Streptococcus sp., and Veillonella sp., was lower among children in intervention day-care centers compared with children in standard day-care centers. In the gut, the relative abundance of Clostridium sensu stricto decreased, particularly among the intervention children. This study shows that a 2-year biodiversity intervention shapes human commensal microbiota, including taxa that have been associated with immune regulation. Results indicate that intervention enriched commensal microbiota and suppressed the potentially pathogenic bacteria on the skin. We recommend future studies that expand intervention strategies to immune response and eventually the incidence of immune-mediated diseases.
Highlights
Today, the vast majority of children in the world live in urban areas with limited access to natural environments (United Nations, 2018)
An increasing number of children living in urban areas are suffering from immune-mediated diseases, including asthma (Ege et al, 2012), type 1 diabetes (Kondrashova et al, 2005), atopy, and allergies (Hanski et al, 2012)
In comparison with rural children, have distinct commensal microbiota, which is hypothesized to be a cause of the high immune-mediated disease incidence among children living in an urban environment (Hanski et al, 2012; Kondra shova et al, 2013; Lehtimaki et al, 2017)
Summary
The vast majority of children in the world live in urban areas with limited access to natural environments (United Nations, 2018). An increasing number of children living in urban areas are suffering from immune-mediated diseases, including asthma (Ege et al, 2012), type 1 diabetes (Kondrashova et al, 2005), atopy, and allergies (Hanski et al, 2012). The underlying cause of these disorders, according to the biodiversity hypothesis, is an imbalance in immune regulation caused by a weak interaction with environmental microbes In this 2-year study, we analyzed bacterial community shifts in the soil surface in day-care centers and commensal bacteria inhabiting the mouth, skin, and gut of children. In the year-one skin swabs, richness of Alpha-, Beta-, and Gammaproteobacteria was higher, and the relative abundance of potentially pathogenic bacteria, including Haemophilus parainfluenzae, Streptococcus sp., and Veillonella sp., was lower among children in intervention day-care centers compared with children in standard day-care centers. We recommend future studies that expand intervention strategies to immune response and eventually the incidence of immunemediated diseases
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