Quorum sensing responses of r-/K-strategists Nitrospira in continuous flow and sequencing batch nitrifying biofilm reactors

A better understanding of r-/K-strategists nitrifiers will help to balance the design and operation of bioprocesses for efficient pollution removal from wastewater. The objectives of study were to investigate the nitrite oxidation biokinetics, biofilm property, microbial community and quorum sensing (QS) of nitrifying biofilm in a continuously flow reactor (CFR) and a sequencing batch reactor (SBR). Results showed that nitrite-oxidizing bacteria were estimated to have a nitrite half saturation constant of 76.23 and 224.73 mu M in CFR and SBR, respectively. High-throughput and metagenomic sequencing results showed that Nitrospira and Candidatus Nitrospira defluvii were the dominated nitrite-oxidizing taxa performing nitrite oxidation in both reactors. Nitrifying biofilm developed in CFR and SBR showed obviously different properties. Biofilm in SBR had an obviously higher ratio of polysaccharide and protein in extracellular polymeric substances, and higher thickness than in CFR. Metagenomics and chemical analysis revealed various types of acyl-homoserine lactone (AHL) circuit genes (e.g., luxI, lasI, hdtS) and four types of AHL signaling substances (e.g., C-6-HSL, C-8-HSL, C-10-HSL and 3-oxo-C-10-HSL) in nitrifying biofilm. The concentrations of these AHLs in biomass and water phases were obviously higher in SBR than that in CFR. Together, AHLs-based QS might affect the formation of nitrifying biofilm and thus contribute to the different biokinetics of Nitrospira in CFR and SBR. Our insights may reveal the molecular mechanism of Nitrospira for different biokinetics, and indicate the AHL association with Nitrospira adaptation to various conditions.

Automated summary

A better understanding of r-/K-strategists nitrifiers is crucial for optimizing the design and operation of bioprocesses for wastewater treatment. This study investigated the nitrite oxidation biokinetics, biofilm properties, microbial community, and quorum sensing (QS) in nitrifying biofilms from a continuously flow reactor (CFR) and a sequencing batch reactor (SBR). The results revealed different nitrite half saturation constants and dominant nitrite-oxidizing taxa in the CFR and SBR. Additionally, the biofilm properties and AHL signaling substances were significantly different between the two reactors. The insights gained from this study provide valuable information on the molecular mechanisms and adaptation of Nitrospira in different biokinetic environments.