Full evaluation of assimilatory and dissimilatory nitrate reduction in a new denitrifying bacterium Leclercia adecarboxylata strain AS3-1: Characterization and functional gene analysis

Abstract Nitrogen (N) transformation is a critical biogeochemical cycle in aquatic ecosystems, where bacterial assimilation and dissimilation (e.g., denitrification) contributes significantly to N removal. In this study, a new bacterial strain Leclercia adecarboxylata AS3-1 capable of efficient N removal was isolated and its N transformation mechanisms were fully evaluated. Strain AS3-1 could utilize nitrate (NO 3 − ) and nitrite (NO 2 − ) as the sole N sources in M9 medium, having an average N removal rate of 2.47 and 2.26 mg L − 1 h − 1 , respectively. Nitrogen balance analysis indicated that most spiked N was transformed to intracellular N by 20.1–56.6% (0.64–1.36 mg) and gaseous N by 29.9–46.8% (0.34–3.17 mg). The optimal conditions for NO 3 − removal were incubation temperature of 30 °C, solution pH of 7.5, C/N ratio of 5 and rotation speed of 150 rpm. Genome sequencing and functional gene annotations identified five operons narKGHJI, nasFEDnirBnasA, narLXKGHJI, norRVW and nirBDCcysG, with two additional genes outside the operons that might have involved in N assimilation and dissimilation in strain AS3-1. Our study provided a new example of diverse N transformation-regulating systems, which could help to better understand bacterial N behaviors in the environment and promote the use of denitrifying bacteria in N removal from waters.