Microbiome in an office building using a cooling trench as an outdoor air duct

Abstract

Subterranean temperature at a depth of 10 m is almost equal to the average outdoor air temperature of the same area. Therefore, if a building cooling trench is used as an outdoor air duct, outdoor air can be cooled in summer and warmed in winter. This energy-saving technique is often used in Japan. However, since the relative humidity in a cooling trench is high, microbe numbers tend to increase in summer. The present study sought to characterize the microbiome status in the cooling trench of such an office building in Japan. Specifically, we performed a metagenomic analysis in which we analyzed DNA directly upon collection from the environment, without intervening cultivation. The results showed the presence of bacteria of the genera Pseudomonas, Lactobacillus, Nesterenkonia, Staphylococcus, Deinococcus, Acinetobacter, Enhydorobacter, and Corynebacterium. Bacteria of the genera Nesterenkonia, Deinococcus, Enhydorobacter, and Corynebacterium predominated on the surface of the trench. Notably, bacteria of the genus Nesterenkonia constituted >50% of the organisms on the surface of the downstream end of the cooling trench. Principal coordinate analysis was used to compare bacterial inhabitants of outdoor air, indoor air from 2nd- and 3rd-floor offices, and the region downstream of the cooling trench. The results suggested that the microbiome of air in this cooling trench influenced indoor air within the building.