Simultaneous nitrogen and phosphorus removal by a novel cold-adapted Acinetobacter bohemicus strain FX-Q2: Performance, mechanism, and potential application

Abstract

A novel cold-adapted bacterium, Acinetobacter bohemicus strain FX-Q2, was isolated from activated sludge and demonstrated efficient simultaneous aerobic removal of nitrogen and phosphorus. The strain could completely remove NH₄⁺-N and PO₄^3–-P from real wastewater within 36 h at 10  °C. Under optimized cultivation conditions (sodium acetate as the carbon source, C/N 10, P/N 0.2, pH 7.5, and 150 r/min) at 10 °C, strain FX-Q2 achieved the highest removal efficiencies for NH₄⁺-N (99.89%), NO₂^–-N (99.84%), NO₃^–-N (94.94%), and PO₄^3–-P (100%) within 48 h. Functional gene annotation revealed that the strain possessed genes associated with three nitrogen metabolic pathways: heterotrophic ammonia assimilation (HAA), assimilatory nitrate reduction (ANRA), and dissimilatory nitrate reduction to ammonium (DNRA), suggesting strain FX-Q2 could assimilate nitrogen via multiple mechanisms. This prediction was substantiated by nitrogen balance analysis, which identified heterotrophic assimilation as the dominant nitrogen removal route, whereas nitrification contributed only marginally. The presence of nitrification activity was further confirmed using enzyme assays. Genomic analysis and enzymatic assays indicated that aerobic phosphorus removal was primarily mediated by ppk1 and ppx-gppA. Phosphorus distribution experiments showed that 50.89%–58.62% of phosphorus was incorporated into the cell membrane, while phosphorus associated with extracellular polymeric substances (EPS) served as a dynamic phosphorus reservoir. Collectively, Acinetobacter bohemicus strain FX-Q2 exhibits the potential for sustainable nutrient removal and recovery in cold-climate bioprocesses.

Graphical abstract

Keywords

Acinetobacter bohemicus / low temperature / simultaneous nitrogen and phosphorus removal / heterotrophic assimilation / metabolic pathways / real wastewater

Highlight

	● A novel cold-adapted bacterium Acinetobacter bohemicus strain FX-Q2 was isolated.
	● Efficient simultaneous removal of N&P under aerobic conditions at 10 °C was achieved.
	● The low-temperature nutrient removal pathway of strain FX-Q2 was elucidated.
	● Heterotrophic nitrogen assimilation was the primary metabolism strategy.
	● Phosphorus was predominantly localized in the cell membrane.

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