This　study　aimed　to　explore　the　dynamics　of　microbial　communities　and　antibiotic　resistance　genes　(ARGs)　during　biofilm　formation　on　polypropylene　random　(PPR),　polyvinyl　chloride　and　stainless　steel　pipes　in　domestic　hot　water　system　(DHWS),　as　well　as　their　interactions.　Full-scale　classification　was　used　to　divide　abundant　and　rare　genera　with　0.1%　and　1%　as　the　thresholds.　The　biofilm　community　structure　presented　a　temporal　pattern,　which　was　mainly　determined　by　conditionally　rare　or　abundant　taxa　(CRAT)　and　conditionally　rare　taxa　(CRT).　The　dynamics　of　microbial　community　during　biofilm　formation　were　observed,　and　the　effect　of　pipe　material　on　conditionally　abundant　taxa　(CAT)　and　CRAT　was　greater　than　CRT　and　rare　taxa　(RT).　CRAT　showed　the　most　complex　internal　associations　and　were　identified　as　the　core　taxa.　Notably,　CRT　and　RT　with　low　relative　abundance,　also　played　an　important　role　in　the　network.　For　potential　pathogens,　17　genera　were　identified　in　this　study,　and　their　total　relative　abundance　was　the　highest　(3.6-28.9%)　in　PPR　samples.　Enterococcus　of　CRAT　was　the　dominant　potential　pathogen　in　young　biofilms.　There　were　36　more　co-exclusion　patterns　(140)　observed　between　potential　pathogens　and　nonpathogenic　bacteria　than　co-occurrence　(104).　A　total　of　38　ARGs　were　predicted,　and　109　negative　and　165　positive　correlations　were　detected　between　them.　Some　potential　pathogens　(Escherichia/Shigella　and　Burkholderia)　and　nonpathogenic　bacteria　(Meiothermus　and　Sphingopyxis)　were　identified　as　the　possible　hosts　of　ARGs.　This　study　is　helpful　fora　comprehensive　understanding　of　the　biofilm　microbial　community　and　ARGs,　and　provides　a　reference　for　the　management　and　biosafety　guarantee　of　newly-built　DHWS.　(C)　2020　Elsevier　B.V.　All　rights　reserved.