Effects of Mn2+ and humic acid on microbial community structures, functional genes for nitrogen and phosphorus removal, and heavy metal resistance genes in wastewater treatment

Considering the wide occurrence of Mn2+ and humic acid (HA) in environmental media, the effects of Mn2+ (5-16 mg/L) and HA (10 mg/L) on microbial community structures, functional genes for nitrogen and phosphorus removal, and heavy metal resistance genes (HMRGs) were investigated in wastewater treatment using sequencing batch bioreactors (SBRs). The treatment efficiencies of influent chemical oxygen demands (COD), NH4+-N, and PO43--P were unaffected during the entire operational processes irrespective of whether Mn2+ and HA were supplied. Although the functional prediction of genetic information via sequencing analysis showed that the microbial activity was not influenced by Mn2+ and HA from different SBRs, the abundance of dominant phyla (Proteobacteria, Actinobacteriota, Firmicutes, and Bacteroidota), classes (Saccharimonadia, Gammaproteobacteria, and Bacilli), and genera (unidentified_Chloroplast, TM7a, Micropruina, Candidatus_Competibacter, Lactobacillus, OLB12, and Pediococcus) was different. Compared to the SBR without Mn2+ and HA supplementation, the abundance of functional genes for nitrogen and phosphorus removal (narG, nirS, nosZ, ppk, and phoD) and HMRGs (corA and mntA) significantly increased under Mn2+ stress, but significantly decreased with the addition of HA except for genes nirS and ppk. The abundance of genes corA and mntA was related to the partially dominant microbes and functional genes, and might be reduced by supplying HA. This study provides insight into the effects of Mn2+ and HA on functional genes for nitrogen and phosphorus removal and HMRGs in wastewater treatment.

Automated summary

This study investigated the effects of Mn2+ and HA on microbial community structures, functional genes, and heavy metal resistance genes in wastewater treatment. The results showed that Mn2+ positively affected genes for nitrogen and phosphorus removal and HMRGs, while HA supplementation decreased the abundance of these genes.