16S amplicon sequencing of air metagenome: Air metagenome samples during and after the 2014 Beijing APEC Summit
PM2.5 samples were collected by high-volume air samplers equipped with PM2.5 fractionating inlets. Particulate matters with aerodynamic diameters of  2.5m were collected on 2025cm2 quartz filters. Sterilized operations and microbial DNA extraction were conducted according to Chen Cao et al.s protocol. The V3-V4 region of the bacteria 16S ribosomal RNA gene were was amplified by PCR using primers 338F and 806R. Purified amplicons were paired-end sequenced (2*250 bp) on an Illumina MiSeq platform according to the standard protocols.