For the metagenomic analyses, 100 mg of each dust sample were aliquoted, and DNA was extracted using the DNeasy PowerLyzer PowerSoil Kit (Qiagen, 12855-50). Tests were performed at three input amounts (50 mg, 100 mg, and 150 mg), whereby 100 mg of material yielded the best output in terms of DNA concentrations and quality, see S1.1.1 (Figure ) for details. The manufacturer's protocol was followed , with the exception that DNA extracts were eluted in 40 µL of sterile DNA-free PCRgrade water instead of 100 µL of Solution C6.