Isolation and identification of a cold-tolerant and aerobic denitrifying bacterium Aeromonas sp. and optimization of denitrification conditions

Abstract:

[Objective] To isolate and screen out the cold-tolerant and aerobic denitrifying bacteria from activated sludge and river sediment in winter, and optimize the key factors that influence denitrification, so as to improve the effect of denitrification at low temperature. [Methods] Cold-tolerant and aerobic denitrifying bacteria were isolated and screened out by enrichment and purification method. Morphological observation and 16S rRNA gene sequence phylogenetic analyses were used to identify the species of the newly isolated strain. Taking the removal rate of NO₃^–-N as the response target, the key factors affecting denitrification, including carbon-nitrogen ratio, temperature, pH and shaking speed, were optimized by Box-Behnken design and response surface regression analysis to determine the optimal culture conditions. [Results] A cold-tolerant and aerobic denitrifying bacterium Z6 was obtained from the river sediment in the cold area of northeast China in winter. The round colony of the strain was white and translucent, and the cell was short rod-shaped, with the size of (0.8–1.6)μm×(0.6–0.8) μm. Gram staining was negative. The strain Z6 was identified as Aeromonas sp. due to the high homology with the 16S rRNA gene sequences of the genus Aeromonas sp.. Based on the response surface analysis, the optimal denitrification conditions of Aeromonas sp. Z6 were 5.9 of carbon-nitrogen ratio at pH 6.8 and 12 ℃ with 155 r/min shaking table speed. Under the optimum conditions, the removal rate of NO₃^–-N was 89.72%, which was not significantly different from the predicted rate (90.34%). [Conclusion] Aeromonas sp. had high denitrification performance under low-temperature conditions, which provided references for biological denitrification of low-temperature wastewater in cold areas.