Effect of formaldehyde exposure on bacterial communities in simulating indoor environments.

Indoor formaldehyde (CHO) exceeding the recommended level is a severe threat to human health. Few studies have investigated its effect on indoor surface bacterial communities, affecting habitants' health. This study used 20-L glass containers to mimic the indoor environment with bacterial inputs from human oral respiration. The behavior of bacterial communities responding to CHO varied among the different CHO levels. The bacterial community structure significantly changed over time in the 0.054 mg·m CHO group, which varied from the 0.1 mg·m and 0.25 mg·m CHO groups. The Chao1 and Shannon index significantly increased in the 0.054 mg·m CHO group at 6 week, while they remained unchanged in the 0.25 mg·m CHO group. At 12 week, the Chao1 significantly increased in the 0.25 mg·m CHO group, while it remained unchanged in the 0.054 mg·m CHO group. Only a few Operational Taxonomic Units (OTUs) significantly correlated with the CHO concentration. CHO-induced OTUs mainly belong to the Proteobacteria and Firmicutes. Furthermore, bacterial communities formed at 6 or 12 weeks differed significantly among different CHO levels. Functional analysis of bacterial communities showed that inferred genes related to chemical degradation and diseases were the highest in the 0.25 mg·m CHO group at 12 weeks. The development of nematodes fed with bacteria collected at 12 weeks was applied to evaluate the bacterial community's hazards. This showed significantly impaired growth in the 0.1 mg·m and 0.25 mg·m CHO groups. These findings confirmed that CHO concentration and exposure time could affect the indoor bacterial community and formed bacterial communities with a possibly more significant hazard to human health after long-term exposure to high CHO levels.