Airborne Bacterial and Eukaryotic Communities in Temuco, Chile, a City Dominated by Residential Wood Combustion

Airborne particulate matter (PM) affects human health, especially in heavily polluted regions. This study focused on Temuco, a city dominated by residential wood combustion in southern Chile. For the first time, we characterized airborne eukaryotic microbial communities in this area, alongside a parallel analysis of bacterial communities, and explored their associations with water-soluble inorganic ions (WSIIs) and meteorological variables. Bacterial and eukaryotic communities were profiled using 16S and 18S rRNA gene sequencing, respectively. The results showed that the mean concentrations of PM_2.5 and PM₁₀ were 75.0 and 87.7 μg/m³, respectively, with PM_2.5 exceeding the Chilean national air quality standards (PM_2.5: 50 μg/m³; PM₁₀: 130 μg/m³), highlighting the persistent fine particulate matter pollution in the region. Among the WSIIs, NO₃^- (5.6 μg/m³), SO₄^2- (2.6 μg/m³), and K⁺ (2.6 μg/m³) were the most abundant, indicating important contributions from secondary aerosol formation and residential biomass burning. At the genus level, Clostridium (6.2%), Hymenobacter (4.3%), and Sphingomonas (4.3%) dominated the bacterial communities, whereas Coriolopsis (41.0%) and Hyphodontia (26.9%) were the predominant eukaryotic taxa. Community composition differed between seasons and particle-size fractions, with seasonal variation appearing to be more pronounced. Correlation analysis and redundancy analysis (RDA) further showed relatively high loadings of SO₄^2- (loading = 0.7146) and temperature (Temp, loading = 0.7101) in the bacterial RDA, and of Cl^- (loading = -0.9054) and SO₄^2- (loading = -0.7176) in the eukaryotic RDA. Overall, these findings provide important insights into the ecology of atmospheric microorganisms and their potential environmental associations in a city dominated by residential wood combustion.