Effect of trace elements and optimization of their composition for the nitrification of a heterotrophic nitrifying bacterium, Acinetobacter harbinensis HITLi7^T, at low temperature

The effects of trace elements on ammonium degradation performance and extracellular polymeric substances (EPS) secretion of Acinetobacter harbinensis HITLi7^T at low temperature were investigated. Response surface methodology (RSM) was applied to obtain the optimal composition of trace elements and analyze their correlation. In this study, the results indicated that the ammonium removal performance could be enhanced by the presence of 0.1 mg L⁻¹ Fe, Mn, or B in pure cultivation. When the concentrations of Fe and Mn were 0.2 mg L⁻¹, the ammonium removal rates of the novel strain HITLi7^T were 0.49 ± 0.01 mg L⁻¹·h⁻¹ and 0.58 ± 0.01 mg L⁻¹·h⁻¹, respectively, while it was the low concentration of 0.05 mg L⁻¹ B that showed the maximum ammonium removal rate (0.56 ± 0.02 mg L⁻¹·h⁻¹) of strain HITLi7^T. The regression model was obtained and the optimal formulation of trace elements was: B 0.064 mg L⁻¹, Fe 0.12 mg L⁻¹, and Mn 0.1 mg L⁻¹. Based on these values, the experimental ammonium removal rate could reach 0.59 mg L⁻¹·h⁻¹, which matched well with the predicted response. The study also found that the addition of trace elements, causing high ammonium removal rates, resulted in a high polysaccharide (PS) ratio in the EPS secreted by Acinetobacter harbinensis HITLi7^T. Especially under the optimal conditions, the PS ratio reached the highest value of 49.9%.