Distinct structureal strategies with similar functional responses of abundant and rare subcommunities regarding heavy metal pollution in the Beiyun river basin

It is unknown how abundant and rare subcommunities found in sediments of urban rivers respond to heavy metal pollutants. We used high-throughput sequencing to understand these response patterns in the Beiyun River, (Beijing, China) which is a heavily polluted urban river. The study area faces a substantially high potential ecological risk, with Cd and Hg being produced at high rates owing to urbanization. Surprisingly, abundant and rare subcommunity structures had opposite response strategies to heavy metals. Abundant subcommunities like Crenarchaeota and Euryarchaeota showed a positive response to heavy metal pollution through synergy with NH4+-N and TP. By contrast, Verrucomicrobia, Fibrobacteres, Berkelbacteria and Euryarchaeota, which constitute rare subcommunities, had a high synergy with NH4+-N and TP in a negative response to heavy metal pollution. However, the functions of both abundant and rare subcommunities showed a similar response to heavy metal pollutants, especially in denitrification processes (nitrate denitrification, nitrite denitrification, nitrous oxide denitrification and denitrification). The abundant subcommunities responded to heavy metal pollution through methanogenesis by CO2 reduction with H2, human pathogens nosocomia, sulfate respiration, photoheterotrophy and dark sulfide oxidation synergy with NH4+-N and TP. Methanogenesis by CO2 reduction with H2, cellulolysis, sulfate respiration, intracellular parasites, nitrate reduction and plant pathogen of the rare subcommunities showed high synergy with NH4+-N and TP in response to heavy metal pollution. Our results clearly indicated that distinct patterns exist between microbial subcommunity structures and functions in response to heavy metal pollutants. Moreover, they support the concept that the denitrification processes are sensitive to heavy metals but are not inhibited by pollution owing to heavy metals in heavily polluted running water ecosystems. Therefore, detailing the structures and functions of the abundant and rare subcommunities enhances the management of pollutants in heavily polluted running water ecosystems at fine geographical scales.