Disruption of Surface Bacterial Communities by Indoor Ambient Sulfur Dioxide

Indoor sulfur dioxide (SO₂) is a common air pollutant that may affect surface-associated bacterial communities. While high concentrations (≥100 ppm) are known to act as disinfectants, the effects of typical indoor concentrations (≤100 ppb) remain unclear. This study investigated SO₂ impacts on bacterial viability, biofilm formation, and community composition across nutrient gradients and relative humidity (RH, 20%-97%) using controlled chamber exposures with <i>Escherichia coli</i> to probe mechanistic responses and real-world kitchen surface communities to assess ecological relevance. Bactericidal effects were strongest on loosely adherent <i>E. coli</i> under nutrient-poor, low-RH (20%) conditions and low cell density (10⁶ CFU/cm²), likely due to increased acidification and sulfate adsorption. At this density and nutrient level, ≥30 ppb of SO₂ significantly reduced viability across all RH levels, while ≤100 ppb did not affect nutrient-rich surfaces at 97% RH or at higher densities (10⁷ CFU/cm²). Biofilm inhibition required 100 ppb, indicating greater resistance than loosely adherent cells. In kitchen surface communities, bacterial abundance declined at 30 ppb on cooking surfaces and at ≥10 ppb on noncooking surfaces at ≤60% RH, with no effect at 97% RH. At 30 ppb, SO₂ reduced bacterial diversity and altered microbial composition, independent of surface type or RH. Ambient SO₂ evidently has an underrecognized impact on indoor-surface microbial communities.