The characteristics of microorganisms in residence in summer and winter among different climate zones, China

Abstract

<p indent="0mm">Indoor microbes have been listed in the category of indoor air pollutants by World Health Organization (WHO) in 1990. Exposure to a high concentration of airborne bioaerosol potentially causes adverse health effects, such as pneumonia, asthma, and allergies. People spend most of their time in residence in their life, so figuring out the characteristic of residential airborne microbes is very important for occupants’ health. However, previous studies mostly focused on indoor microorganisms in public buildings, while very little work has been done on the characteristics of indoor airborne bacteria and fungi in residence. In this study, we investigated the indoor airborne bacterial concentration, fungal concentration, and taxonomic diversity of residences in summer and winter among five different climate zones across China, as well as the community structure, and revealed the correlations between indoor airborne microbial characteristics (concentrations and taxonomic diversity) and geographical location by using polynomial fitting. Culturing and sequencing methods were combined in this study, for which we collected 376 culturable samples and 168 sequencing samples of bacteria and fungi each. We found the bacterial concentrations between summer and winter were significantly different in the hot summer &amp; cold winter climate zone and the hot summer &amp; warm winter climate zone, whereas there was no significant difference between different seasons among different climate zones for fungal concentrations. The bacterial concentrations in the hot summer &amp; cold winter zone (Nanjing, 875±553 CFU/m³) and hot summer &amp; warm winter (Shenzhen, 758±473 CFU/m³) were significantly higher than those in the other climate zones in summer (<italic>P </italic>&lt; 0.05); the lowest bacterial concentrations in winter were found in hot summer &amp; cold winter (Nanjing, 191±119 CFU/m³). For fungi, the highest concentrations were found in the severe cold climate zone (Harbin, 743±798 CFU/m³) and cold climate zone (Lhasa, 1369±1380 CFU/m³) in summer; while the highest was only found in the severe cold climate zone (Harbin, 654±493 CFU/m³) in winter. We also found that the bacterial diversity in the hot summer &amp; cold winter climate zone was significantly different between summer and winter; the fungi diversity in the hot summer &amp; cold winter climate zone and hot summer &amp; warm winter climate zones was significantly different between summer and winter. For bacteria, the lowest taxonomic diversity in summer was found in severe cold climate zone and the highest was found in hot summer &amp; cold winter climate zone; the lowest taxonomic diversity in winter was found in severe cold climate zone and hot summer &amp; cold winter climate zone. For fungi taxonomic diversity, the highest values were found in severe cold climate zone and hot summer &amp; cold winter climate zone in summer; the highest values were found in cold climate zone and hot summer &amp; warm winter climate zone in winter. We analyzed the community structure of bacteria and fungi at the phylum level. The TOP 4 bacterial species and TOP 3 fungal species between different climate zones in summer and winter were similar. The TOP 4 bacteria species in residences were <italic>Bacteroidetes</italic>, <italic>Proteobacteria</italic>, <italic>Firmicutes</italic>,<italic> </italic>and <italic>Actinobacteria</italic>. The TOP 3 fungi species were <italic>Ascomycota</italic>, <italic>Basidiomycota</italic>, and <italic>Zygomycota</italic>, except for Beijing, which is located in a cold climate zone. By analyzing the correlations between indoor microbial characteristics and geographical location, we found the variation of indoor microbial diversity with latitude was opposite in summer and winter. In summer, indoor bacterial concentrations and diversity first increased and then decreased with the increase of longitude, which was opposite to the trend of fungi. There was no correlation between winter bacterial concentrations and geographical location.