Abstract: We tested the bacterial diversity of filter membrane samples in freshair purification systems in Licheng，Jinan，at different times, and analyzed the potential risk of secondary microbial contamination in indoor fresh-air purification systems.The bacterial diversity of three air-filtration membrane samples obtained from the fresh-air purification system used in Licheng at different times was analyzed using the 16S rDNA amplicon sequencing technology.The dominant bacterial phyla were Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes. The dominant genera in three samples were Paracoccus, Sphingomonas, Bacillus, Methylobacterium,and Bifidobacterium. With the extension of the usage time of the fresh-air purification system, the relative abundance ratio among the dominant fungi did not change significantly, but the total abundance showed an increasing trend, indicating that the microorganism in indoor air was abundant in this area and the community structure did not change much in the long term. For the air-filtration membrane used in the area for 12 months, Rheinheimer, Lactobacillus, and Acinetobacter were also the dominant genera. Moreover, the relative abundance of opportunistic pathogen Moraxella osloensis was high, which indicatesthe indoor fresh-air purification system has a certain risk of microbial secondary pollution when it is used for 12 months. The results of this study can guide residents to prevent and control indoor-air secondary pollution.

Key words: indoor air, fresh-air purification system, secondary microbial contamination, bacterial diversity, 16S rDNA amplicon sequencing technology