Pseudomonas mendocina LYX: A novel aerobic bacterium with advantage of removing nitrate high effectively by assimilation and dissimilation simultaneously

Highlights

• Pseudomonas mendocina was first reported for aerobic nitrate removal.

• It removed 90% of NO₃⁻-N in 24 h under aerobic conditions.

• This strain converted NO₃⁻-N to bio-nitrogen (37.9%) and gaseous nitrogen (49.7%).

• Inoculation of this strain increased sludge denitrification rate by 4.3 times.

Abstract

The problem of nitrate accumulation in aerobic tank and total nitrogen excessive discharge in effluent was very common in traditional livestock and poultry farming wastewater treatment systems owing to the lengthy process flow and low process control level. A strain LYX of aerobic bacterium was isolated from the activated sludge of a wastewater treatment system in a pig farm, which could remove nitrate effectively in aerobic tank and was identified Pseudomonas mendocina by 16S rRNA sequencing. Under the condition of nitrate as the sole nitrogen source, this strain removed over 90% of NO₃⁻-N with an initial concentration of 110 mg/L under aerobic conditions within 48 hours. Among them, 37.9% of NO₃⁻-N was assimilated into Bio-N, about 51.9% was reduced to gaseous nitrogen and less than 0.5% of nitrogen was replaced by NO₂⁻-N and NH₄⁺-N, 9.7% NO₃⁻-N remained in the effluent at the end. At the same time, four key genes (napA, nirK, norB and nosZ) related to nitrate nitrogen removal were expressed during the denitrification process of P. mendocina LYX, in which the transcription level of the indicator genes of this aerobic denitrifying bacterium (napA) was the highest. In addition, it was found with the ¹⁵N tracer technique that inoculation of this strain on sludge increased the amount of nitrogen loss from 9.26 nmol N/(g·h) to 23.835 nmol N/(g·h). Therefore, P. medocina LYX is a potential bioagent for advanced nitrogen removal by assimilating and reducing nitrate simultaneously in aerobic tanks.

Graphical abstract

Keywords

Pseudomonas mendocina / Aerobic nitrate removal / ¹⁵N tracing technique / Denitrification assimilatively and disimilatively / Aerobic denitrifying genes

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Acknowledgements

This work was financially supported by the National Key R & D Program of China (Grant No.2016YFC0400706), the National Natural Science Foundation of China (Grant Nos. 41671481 and 41977340) and the Science & Technology Plan Project of Guangdong (No. 2016B020240003); Key-Area Research and Development Program of Guangdong Province (No. 2019B110205004). We would like to thank Professor Hong YG and Dr. Wu JP (Guangzhou University) for their warmful help on ¹⁵N labeling test and analysis.

Electronic Supplementary Material

Supplementary material is available in the online version of this article at https://doi.org/10.1007/s11783-020-1349-3 and is accessible for authorized users.

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