Metagenomic and extracellular polymeric substances analysis reveals the mechanism of exogenous N-hexanoyl-L-homoserine lactone in alleviating the inhibition of perfluorooctanoic acid on anammox process

To alleviate the negative effects of perfluorooctanoic acid (PFOA) on nitrogen removal via anaerobic ammonia oxidation (anammox), an exogenous signaling factor (N-hexanoyl-L-homoserine lactone, C6-HSL) was introduced into an anammox reactor. Results showed that 2 mu mol/L C6-HSL promoted the nitrogen removal efficiency of the anammox reactor under PFOA stress, with the removal efficiencies of ammonia and nitrite increasing from 79.7 +/- 4.8 % and 80.8 +/- 3.8 %, to 94.4 +/- 4.3 % and 97.1 +/- 3.8 %. Exogenous C6-HSL enhanced the compactness of the extracellular proteins, and improved the sludge hydrophobicity. Meanwhile, C6-HSL resulted in a microbial shift, with the relative abundance of Planctomycetes increasing from 30.2 % to 49.5 %. Candidatus Kuenenia stuttgartiensis replaced Candidatus Brocadia sp. BL1 as the dominant species, while the available space for other nitrogen-removing bacteria was reduced. Exogenous C6-HSL promoted the expression of anammox-related genes, such as hzsB and hdh, while denitrifying genes were down-regulated. In addition, the relative abundance of HdtS, which synthesizes AHLs, increased by 0.02446%.