A research article written by Marja Roslund et al. has been published in Environment International. The study is based on the fact that in modern urban environments children have a high incidence of inflammatory disorders, including allergies, asthma, and type 1 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 study, the authors analyzed bacterial community shifts in the soil surface in day-care centers and commensal bacteria inhabiting the mouth, skin, and gut of children. Two different day-care environments were compared: 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.
The results show that the 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 gut, the relative abundance of Clostridium sensu stricto decreased, particularly among the intervention children. Hence, the 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.