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Pseudomonas sp. AOB-7 utilizes PHA granules as a sustained-release carbon source and biofilm carrier for aerobic denitrification of aquaculture water


Nitrate accumulation causes long-time threat to aquatic animals in recirculating aquaculture system (RAS); thus, nitrate removal is also required in RASs. However, the lack of carbon sources makes denitrification difficult to function. Nitrate removal performance of an aerobic denitrifying and extracellular polyhydroxyalkanoate depolymerase–producing bacterium, Pseudomonas sp. AOB-7, using polyhydroxyalkanoate (PHA) granules as a solid sustained-release carbon source in RAS was evaluated. With the initial nitrate-N concentration of 140 mg/L, the high denitrification rates of 0.056 g NO3-N L−1 day−1 and 0.035 g NO3-N L−1 day−1 were achieved in denitrification medium containing poly-β-hydroxybutyrate (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), respectively. Significant erosions and pits formed on the surface of the granules made them a good biofilm carrier for AOB-7, and 3-hydroxybutyrate (3-HB) monomer was the major product released to aquatic phase, which was benefit to animals. SEM photos showed that AOB-7 entered and attached on the inside of the PHA particle holes. A 4-week application trial was conducted to reveal the effects of PHB (AOB-7) denitrifying agent and 3-HB produced on growth of zebrafish (Brachydanio rerio) by adding 0.1% (w/v) PHB (AOB-7) denitrifying agent. Result indicated that PHB (AOB-7) denitrifying agent can significantly reduce nitrate-N content in RASs. Compared with the control group, feed coefficient ratio reduced by 18% and weight gain ratio increased by 29% in the PHB (AOB-7) denitrifying agent group. 3-HB monomer produced during the denitrification was speculated to function as a prebiotic and promote zebrafish growth.

Key Points

AOB-7 showed a good aerobic denitrifying ability on PHA granules as sustained-release C source.

PHB (AOB-7) denitrifying agent can significantly reduce nitrate content in RAS.

R-3-HB monomer was the major product released to aquatic phase and function as a prebiotic.

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This study was supported by the Biological Resources Program, Chinese Academy of Sciences (KFJ-BRP-009).

Author information

XYG performed the experiments, analyzed the data as well as results, and wrote the manuscript. YL isolated strain AOB-7 used in this work. LLM contributed analytical tools. ZPL supervised all the experiments and revised the manuscript. All authors read and approved the final manuscript.

Correspondence to Zhi-Pei Liu.

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The authors declare that they have no conflict of interest.

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This article does not contain any studies with human participants performed by any of the authors. Zebrafish (Brachydanio rerio) was used in the study. All applicable international, national, and/or institutional guidelines for the care and use of animals were followed.

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Gao, X., Liu, Y., Miao, L. et al. Pseudomonas sp. AOB-7 utilizes PHA granules as a sustained-release carbon source and biofilm carrier for aerobic denitrification of aquaculture water. Appl Microbiol Biotechnol (2020).

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  • Denitrification
  • Sustained-release carbon source
  • Biofilm carrier
  • 3-HB monomer