Mechanism of microbial metabolic responses and ecological system conversion under different nitrogen conditions in sewers

Nitrogen plays a central role in the sewer ecosystem, and the bioconversion of nitrogen can signifi-cantly affect bioreactions in sewers. However, the mechanisms underlying the involvement of nitrogen associated pollutants in sewer ecosystems remain unknown. In this study, the effects of two typical nitrogen ratios (organic/inorganic nitrogen: 7/3 (Group A) and 3/7 (Group B)) on carbon, nitrogen, and sulfur bioconversions were investigated in a pilot sewer. The distribution of amino acids, such as proline, glycine and methionine, was significantly different between Groups A and B, and carbon-associated communities (based on 16S rRNA gene copies) were more prevalent in Group A, while sulfur and nitrogen-associated communities were more prevalent in Group B. To explore the effect of nitrogen on microbial response mechanisms, metagenomics-based methods were used to investigate the roles of amino acids involved in carbon, nitrogen, and sulfur bioconversion in sewers. Proline, glycine, and tyrosine in Group A promoted the expression of genes associated with cell membrane transport and increased the rate of protein synthesis, which stimulated the enrichment of carbon-associated communities. The transmembrane transport of higher concentrations of alanine and methionine in Group B was essential for cell metabolism and nutrient transport, thereby enriching nitrogen and sulfur-associated communities. In this investigation, insights into carbon, nitrogen and sulfur bioconversions in sewer ecosystems were revealed, significantly improving the understanding of the sewer ecosystem within a community context. (C) 2020 Elsevier Ltd. All rights reserved.