Characterization of the Nitrogen Removal Potential of Two Newly Isolated Acinetobacter Strains under Low Temperature

Abstract

Excess nitrogen and phosphorus in the water causes several ecological problems for nutrients. Biological nitrogen removal is an economical and efficient way to prevent excessive nitrogen in the environment. For most areas of China, temperatures are usually lower than 20 °C except during the summertime. It is necessary to discover microbes that can efficiently remove nitrogen at low temperatures. In this study, two Acinetobacter strains were isolated from a sample in a wastewater tank in Taizhou for their capabilities to remove NO3−–N and NO2−–N at 15 °C. Heterotrophic nitrification experiments showed that both strains could efficiently remove nitrogen from the culture medium. The maximum removal rates of NH4+–N were 3.15 mg/L·h and 4.74 mg/L·h for heterotrophic nitrification by the strains F and H, respectively. Strain H grew faster and removed both nitrite and nitrate more efficiently than strain F. Genome sequencing showed that strains F and H could be classified into Acinetobacter johnsonii and Acinetobacter bereziniae, respectively. NO2−–N (100 mg/L) was completely removed in 3 days by strain H. The maximum NO3−–N removal rate was 3.53 mg/L·h for strain F. When strain H was cultured in a broth with 200 mg/L NO3−–N, 97.46% of NH4+–N (200 mg/L) was removed in 5 days, and the maximum NH4+–N removal rate was 4.04 mg/L·h. Genomic sequence analysis showed that both the strains lacked genes involved in the denitrification pathway that transforms NO3− into N2. This implies that nitrate or nitrite is removed through the nitrogen assimilation pathway. Genes responsible for nitrate assimilation are clustered together with molybdopterin cofactor biosynthesis genes. Strain H contains fewer resistance genes and transfer elements. All the above data demonstrate that strain H is a promising candidate for nitrogen removal at lower temperatures. But there is still a lot to be done to systematically evaluate the potential of A. bereziniae strain H in treating wastewater at a pilot scale. These include the long-term performance, environmental tolerance, and nitrogen removal efficiency in wastewater. And the application of these Acinetobacter strains in diverse wastewater treatment settings might require careful optimization and real-time monitoring.