Nitrogen removal capability and mechanism of a novel low-temperature-tolerant simultaneous nitrification-denitrification bacterium Acinetobacter kyonggiensis AKD4

A low-temperature-tolerant simultaneous nitrification-denitrification bacterial strain of <i>Acinetobacter kyonggiensis</i> (AKD4) was identified. It showed high efficiency in total nitrogen (TN) removal (92.45% at 10°C and 87.51% at 30°C), indicating its excellent low-temperature tolerance. Transcriptomic analysis revealed possible metabolic mechanisms under low-temperature stress. Genes involved in cell growth, including ATP synthase (<i>atpADGH</i>), amino acid (<i>glyA</i>, <i>dctA</i>, and <i>ilvE</i>), and TCA cycle metabolism (<i>gltA</i>, <i>fumC</i>, and <i>mdh</i>) were remarkably upregulated from 1.05-3.44-fold at 10°C, suggesting that their actions enhance survivability at low temperatures. The expression levels of genes associated with nitrogen assimilation (<i>glnAE</i>, <i>gltBD</i>, and <i>gdhA</i>), nitrogen metabolism regulation (<i>ntrC</i>, <i>glnB</i>, and <i>glnD</i>), and denitrification processes (<i>napA</i>) were increased from 1.01-4.38-fold at 10°C, which might have contributed to the bacterium's highly efficient nitrogen removal performance at low temperatures. Overall, this study offers valuable insights into transcriptome, and enhances the comprehension of the low-temperature-tolerant mechanism of simultaneous nitrification and denitrification processes.