Particle size transfer of antibiotic resistance genes in typical processes of municipal wastewater treatment plant

Occurrence and transfer of antibiotic resistance genes (ARGs) was investigated concerning sludge particle size in a typical wastewater treatment plant, and the roles of vertical (VGT) and horizontal gene transfer (HGT) in the spread of ARGs were explored. Results showed that although membrane bioreactor (MBR) effectively reduced the relative abundance of ARGs in the water phase, it concurrently enriched ARGs in MBR sludge, particularly for the largest-size particles (>150 mu m). A decreasing trend in the relative abundance of ARGs was observed along with the decrease of sludge particle size, and larger-size particle sludge (>106 mu m) formed a relatively stable composition of ARGs, while ARGs on smaller-size particle sludge (6.5-106 mu m) fluctuate rapidly. Particle size does not affect the abundance distribution patterns or assembly mechanisms of ARGs as deterministic processes. The smallest-size particles were the primary attachment site for bacterial pathogens with highest diversity. Larger-size particle sludge (>106 mu m) showed higher frequency of HGT, with Proteobacteria as the dominant hosts for this process.