Relationship between the Microbiome and Indoor Temperature/Humidity in a Traditional Japanese House with a Thatched Roof in Kyoto, Japan

Makoto Kokubo,Jun Noda,So Fujiyoshi,Daisuke Ogura,Fumito Maruyama,Ayako Fujieda,Makiko Nakajima

doi:10.3390/d13100475

Abstract

In our living environment, there are various microorganisms that are thought to affect human health. It is expected that excessive microbial suppression can have a negative effect on human health and that the appropriate control of the microbiome is beneficial to health. To understand how the physical environment, such as temperature and relative humidity, or housing itself affects the microbiome in a rural house, we measured temperature and humidity and collected microbial samples in a traditional Japanese house with a thatched roof. The relative humidity of outdoor air was over 60% most of the day throughout the year. Indoor and outdoor air temperature and humidity were closer to each other in summer than in winter. The DNA concentration of indoor surfaces correlated with the relative humidity, especially with the lowest annual relative humidity. In the thatched roof, outside surface relative humidity often reached 100%, and the occurrence of condensation can affect the DNA concentrations. A high percentage of archaea were detected in the house, which is not a common characteristic in houses. In addition, the microbial community was similar outdoors and indoors or in each room. These characteristics reflect the occupants’ behaviour, including opening the windows and partitions in summer. In the future, it will be necessary to conduct continuous surveys in various houses, including traditional and modern houses, in Japan.

Highlights

The house was ventilated by opening the windows in summer and heated by a wood burning stove in winter, so the indoor air temperature and relative humidity were closer to the outdoor air in summer than in winter
The high thermal insulation, the high thermal capacity and the shading effect of the thatched roof, which is a characteristic of Japanese traditional houses, moderated the indoor air temperature rise in summer
The DNA concentration of microorganisms was greater on the earth floor surface than on indoor surfaces

Summary

Introduction

Risk management for human health in the field of architecture is mainly based on air quality control, such as temperature/humidity control and dilution of carbon dioxide and VOCs by ventilation, and there has been little investigation from the viewpoint of microbiology in public health. Some studies have been conducted on methods of preventing mould growth and material degradation of exterior walls. Abe et al evaluated the rate of mould growth in a given location based on temperature and relative humidity data [2]. Another study developed models for predicting mould growth with transient temperature and humidity conditions [3]. There is a mathematical model for simulating mould growth on wood materials [4]. Research on bacteria and viruses has focused on specific species, such as pathogens, and suppressing them. The survival rate of influenza viruses is higher at low humidity and low temperature [8,9] and the infection rate is higher at low humidity and low temperature [10]

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Conclusion