Transformation and drive mechanism of nitrogen functional genes at estuaries in dry and wet seasons.

The nitrogen cycle plays a vital role in maintaining ecological health and biodiversity. In aquatic systems, nitrogen transformation genes significantly contribute to biological nitrogen cycling. Although the function of these genes is known to be influenced by environmental factors, there is limited research exploring the relationship between nitrogen transformation genes and environmental factors. Therefore, the correlations, between nitrogen transformation genes and environmental factors, were investigated at the estuaries of Chaohu lake (China) in different seasons. The results showed that the values of temperature, pH, organic compounds, nitrogen, and dissolved oxygen were higher in dry season, whereas the abundance of the genes was lower in dry season. In addition, the abundance of the anaerobic ammoxidation gene was much lower than the nitrification gene and denitrification gene. The results indicated that biological nitrification and denitrification were the primary mechanisms for nitrogen removal at estuaries in different seasons, and the reduction of nitric oxide may be a limiting step in the denitrification process. The Co-occurrence Network and Mantel test indicated that, during the dry season, the temperature was the primary driver of ammonification and nitrification functions, the NO3- and NO2- were the primary drivers of denitrification, and the total nitrogen (TN) and NH4+ were the main drivers of anaerobic ammonia oxidation. During the wet season, the dissolved oxygen was the primary driver of ammonification and nitrification functions, the chemical oxygen demand was the primary driver of denitrification, and the TN was the main driver of anaerobic ammonia oxidation. This study provides valuable insights into nitrogen cycling in surface water, contributing to a better understanding of this important process.

Combined effect of tetracycline and copper ion on catalase activity of microorganisms during the biological phosphorus removal.

Microbial catalase is a key enzyme that affects the activities of microorganisms, and the catalase activity is affected by pollutants in wastewater. However, the effects of mixed pollutants on catalase activity are rather complex. To reveal the effect of the mixed pollutants on catalase activity of microorganisms, the present study investigated tetracycline and copper ion as pollutants during the biological phosphorus removal. Three concentration ratios of tetracycline and copper ion and 27 different concentration gradients were designed through the direct equipartition ray and the dilution factor method. The effects of mixed pollutants on the catalase activity of microorganisms were analyzed by the nonlinear regression equation and concentration-addition model. The results showed that, with the increase of actuation duration and the pollutant concentration, the inhibitory effects on the catalase activity of microorganisms obviously increased, which indicated that the inhibitory effects are concentration-dependent and time-dependent. The concentration-addition model suggested that when the ratio was 0.297, the combined effect of mixed pollutants on the activity of microbial catalase was mainly antagonism. When the ratio is 0.894, the combined effect was mainly additivity. When the ratio was 2.676, the combined effect transformed from synergism to additivity and antagonism. The study of the combined effects of tetracycline and copper ion on the catalase activity is helpful to further study their ecotoxicological mechanisms in wastewater treatment.