Exogenous Folate Supplementation Weakens Cross-Feeding and Enriches Marine Anammox Bacteria in Marine Wastewater Treatment

Vollständiger Abstract

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Abstract Cross-feeding, defined as the exchange of metabolites within the microbiome, plays a critical role in the promotion of bacterial activity and growth. Marine anammox bacteria (MAB) possess natural advantages for the treatment of marine wastewater (MW). Herein, the folate-mediated cross-feeding mechanism in MAB-based microbiome was first elucidated under salt stress. The total nitrogen removal rate notably reached 5.2 kg/(m3·d) at the optimal exogenous folate concentration (1.1 mg/L). The stoichiometric ratios of marine anammox (ΔNO2––N/ΔNH4+–N = 1.30, ΔNO3––N/ΔNH4+–N = 0.24) ultimately stabilized around the theoretical values with exogenous folate addition. Besides, exogenous folate markedly enriched the relative abundance of MAB, achieving a remarkable 4.4-fold increase. A metabolic interaction network was elucidated among MAB and their symbionts. Based on metagenomic analysis, bacteria affiliated with Pseudomonadota and Bacteroidota possessed the genetic potential to supply folate for MAB, which is involved in the Wood–Ljungdahl pathway for CO2 fixation in anammox. In resource exchange, MAB secreted extracellular public goods to them. However, with exogenous folate addition, this resource exchange was substantially weakened. MAB reduced the secretion of extracellular public goods for resource exchange and reallocated more energy toward cellular growth during the metabolic exchange interactions. This weakened cross-feeding interaction was further supported by a marked decrease in extracellular protein concentration. This work deepened the understanding of folate-mediated cross-feeding between MAB and symbiotic bacteria and provided a promising strategy to improve the nitrogen removal through MAB in MW treatment.