Plant-derived root exudates enhance extracellular and intracellular metabolism of rhizosphere anammox bacteria: Implication for intensified contributions in constructed wetlands.

Abstract

In constructed wetlands (CWs), plant-derived root exudates (REs) profoundly influence anammox community and its contribution; however, the effect of dynamic changes in REs driven by plant growth on the extracellular and intracellular properties of anammox bacteria remain unclear. Herein, we constructed CWs microcosms incubated with typical rhizosphere REs levels across distinct plant growth stages to investigate the regulation of REs on anammox metabolism. The results showed that REs stimulated the anammox capacity, with activity (0.2 ± 0.1 g NH4+-N/gVSS/d, p < 0.001) and abundance (1.9 × 1011 ± 4.8 × 109 copies/g dry sludge, p < 0.05) at plant flowering stage, which attributed to two pathways. First, quorum sensing-associated regulation potentially contributed to denser anammox granule structures, along with increased extracellular polymeric substances (EPS) (41.2 mg/g) and elevated α-helix/(β-sheet + random coil) ratio (37.4%). Second, REs strengthened EPS-mediated extracellular electron exchange capacity in the Candidatus_Brocadia-dominated anammox consortium (34.9%, p < 0.001), along with upregulated electron transfer-related genes and elevated electrochemical activity. This further promoted core nitrogen conversion (hzs, 8.5-fold), carbon fixation (fdhA, 3.3-fold), and metabolic potential for dissimilatory nitrate reduction to ammonium (nrfA, 26.9%). Above dual regulation ultimately boosted a high anammox contribution (82.8-90.5%) and nitrogen removal efficiency (94.0-97.4%). This study advances our understandings of REs-mediated regulation of anammox bacterial colonization and ecological functions, and proposes a promising engineering strategy for intensifying anammox-driven nitrogen removal in CWs based on plant REs properties.