According to the hygiene and biodiversity hypotheses, increased hygiene levels and reduced contact with biodiversity can partially explain the high prevalence of immune-mediated diseases in developed countries. A disturbed commensal microbiota, especially in the gut, has been linked to multiple immune-mediated diseases. Previous studies imply that gut microbiota composition is associated with the everyday living environment and can be modified by increasing direct physical exposure to biodiverse materials. In this pilot study, the effects of rural-second-home tourism were investigated on the gut microbiota for the first time. Rural-second-home tourism, a popular form of outdoor recreation in Northern Europe, North America, and Russia, has the potential to alter the human microbiota by increasing exposure to nature and environmental microbes. The hypotheses were that the use of rural second homes is associated with differences in the gut microbiota and that the microbiota related to health benefits are more diverse or common among the rural-second-home users. Based on 16S rRNA Illumina MiSeq sequencing of stool samples from 10 urban elderly having access and 15 lacking access to a rural second home, the first hypothesis was supported: the use of rural second homes was found to be associated with lower gut microbiota diversity and RIG-I-like receptor signaling pathway levels. The second hypothesis was not supported: health-related microbiota were not more diverse or common among the second-home users. The current study encourages further research on the possible health outcomes or causes of the observed microbiological differences. Activities and diet during second-home visits, standard of equipment, surrounding environment, and length of the visits are all postulated to play a role in determining the effects of rural-second-home tourism on the gut microbiota.

2nd Faculty of Medicine Charles University 5 Úvalu 84 150 06 Prague 5 Czech Republic

Department of Medicine Karolinska University Hospital Huddinge 141 86 Stockholm Sweden

Ecosystems and Environment Research Programme Faculty of Biological and Environmental Sciences University of Helsinki Niemenkatu 73 15140 Lahti Finland

Faculty of Medicine and Health Technology Tampere University Arvo Ylpön katu 34 33520 Tampere Finland

Natural Resources Institute Finland Itäinen Pitkäkatu 4 A 20520 Turku Finland

School of Agriculture and Biology Shanghai Jiao Tong University 800 Dongchuan RD Minhang District Shanghai 200240 China

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Using patterns of shared taxa to infer bacterial dispersal in human living environment in urban and rural areas