Internal mechanism of microbial nitrogen removal under prolonged low-temperature stress: A focus on microbial communities, metabolic pathways, and microbial function

Low temperature restricts the stable treatment of wastewater in alpine and high-altitude regions. However, the internal mechanism of microbial functional succession at low temperatures remains unknown. To illustrate the internal mechanism by which low temperatures affect wastewater treatment, high-throughput 16S and metagenomic sequencing were employed. Results revealed that microorganisms effectively removed pollutants under prolonged low-temperature stress (3-8 degrees C). The removal efficiencies for chemical oxygen demand, NH4+-N, and total nitrogen were 80.80 %-95.18 %, 87.91 %-99.82 %, and 32.67 %-69.88 %, respectively. The relative abundance of Nitrospira and Nitrosomonas increased by 102.50 % and 276.92 %, respectively. Additionally, the relative abundance of heterotrophic nitrobacteria, including Terrimonas, Rhodobacter, and Ferribacterium, increased significantly, with values increasing by 34.63 %, 22.04 %, and 129.64 %, respectively. These bacteria became dominant. Metagenomic analysis revealed that low temperatures can inhibit membrane transfer. However, the functional genes for electron production and electron carriers were upregulated, thus promoting the ability of microorganisms to metabolize nitrogen. Moreover, the abundance of functional genes involved in extracellular electron transfer (pili, c-type cytochromes, and flagella) increased, which improved the nitrogen removal capacity. This study provides novel perspectives on the internal mechanism of microbial nitrogen removal under prolonged low-temperature stress.