Abstract
Quorum sensing (QS) is a widespread regulatory mechanism in bacteria used to coordinate target gene expression with cell density. Thus far, little is known about the regulatory relationship between QS and cell density in terms of metabolic pathways in Hafnia alvei H4. In this study, transcriptomics analysis was performed under two conditions to address this question. The comparative transcriptome of H. alvei H4 wild-type at high cell density (OD600 = 1.7) relative to low cell density (OD600 = 0.3) was considered as growth phase-dependent manner (GPDM), and the transcriptome profile of luxI/R deletion mutant (ΔluxIR) compared to the wild-type was considered as QS-mediated regulation. In all, we identified 206 differentially expressed genes (DEGs) mainly presented in chemotaxis, TCA cycle, two-component system, ABC transporters and pyruvate metabolism, co-regulated by the both density-dependent regulation, and the results were validated by qPCR and swimming phenotypic assays. Aside from the co-regulated DEGs, we also found that 59 DEGs, mediated by density-independent QS, function in pentose phosphate and histidine metabolism and that 2084 cell-density-dependent DEGs involved in glycolysis/gluconeogenesis and phenylalanine metabolism were influenced only by GPDM from significantly enriched analysis of transcriptome data. The findings provided new information about the interplay between two density-dependent metabolic regulation, which could assist with the formulation of control strategies for this opportunistic pathogen, especially at high cell density.
Highlights
Quorum sensing (QS) is a cell to cell communication system that allows bacteria to coordinate gene expression in response to cell density, which is mediated by diffusible chemical signals such as acyl-homoserine lactones (AHLs) (Goo et al, 2015)
We have reported that the QS systems of Hafnia alvei H4 consists of AHLs synthase encoded by luxI gene and AHLs homologous receptors encoded by luxR gene (Li X. et al, 2019), which involved in the density-dependent biological processes including food spoilage and virulence formation
We could preliminarily conclude that the regulation of growth phase-dependent manner (GPDM) was more complex than that of luxI/R-mediated QS at the transcriptional level, indicating GPDM involved in more metabolic pathways
Summary
Quorum sensing (QS) is a cell to cell communication system that allows bacteria to coordinate gene expression in response to cell density, which is mediated by diffusible chemical signals such as acyl-homoserine lactones (AHLs) (Goo et al, 2015). The concentration of AHLs increases as cell density increases, leading to the coordinated expression of various genes when the concentration of AHLs reaches a certain level (Mellbye et al, 2016). Transcriptome Reveals QS Metabolic Pathways with QS-controlled genes are often required for survival and/or virulence in several bacteria, such as motility, biofilm formation, colonization, adhesion, virulence factor secretion and nutrient acquisition (Goo et al, 2015; Khider et al, 2019). The increase of cell density can significantly increase the expression of hcnABC (hydrogen cyanide synthase genes), and reach its optimal levels during the transit from exponential to stationary growth phase of Pseudomonas aeruginosa (Castric et al, 1979). As for the above density-dependent regulation, QS and GPDM, our understanding of how they influence the direction of metabolism is in its infancy
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