Diverse microbial communities coexist in the partial nitritation–anaerobic ammonium oxidation (PNA) process, in which nitrogen metabolism and information exchange are two important microbial interactions. In the PNA process, the existence of diverse microorganisms including nitrifiers, anammox bacteria, and heterotrophs makes it challenging to achieve a balanced relationship between anaerobic ammonium oxidation bacteria and ammonia oxidizing bacteria. In this study, potential microbial functions in nitrogen conversion and acyl‐homoserine lactones (AHLs)‐based quorum sensing (QS) in PNA processes were examined. Candidatus_Kuenenia and Nitrosomonas were the key functional bacteria responsible for PNA, while Nitrospira was detected as the dominant nitrite oxidizing bacteria (NOB). Heterotrophs containing nxr might play a similar function to NOB. The AHLs‐QS system was an important microbial communication pathway in PNA systems. N‐octanoyl‐L‐homoserine lactone, N‐decanoyl homoserine lactone, and N‐dodecanoyl homoserine lactone were the main AHLs, which might be synthesized by nitrogen converting microorganisms and heterotrophs. However, only heterotrophs had the potential to sense and degrade AHLs, such as Saccharophagus (sensing) and Leptospira (degradation). These results provide comprehensive information about the possible microbial functions and interactions in the PNA system and clues for system optimization from a microbial perspective.

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  Potential functions of anammox bacteria, nitrifiers, and heterotrophs were revealed.
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  Diverse nitrogen conversion and AHLs‐quorum sensing related genes were detected.
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  Anammox bacteria and AOB played important roles in the AHLs synthesis process.
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  Heterotrophs could sense and degrade AHLs during information exchange.