Lysine acetylation regulates the AT-rich DNA possession ability of H-NS.

H-NS, the histone-like nucleoid-structuring protein in bacteria, regulates the stability of the bacterial genome by inhibiting the transcription of horizontally transferred genes, such as the type III and type VI secretion systems (T3/T6SS). While eukaryotic histone posttranslational modifications (PTMs) have been extensively studied, little is known about prokaryotic H-NS PTMs. Here, we report that the acetylation of H-NS attenuates its ability to silence horizontally transferred genes in response to amino acid nutrition and immune metabolites. Moreover, LC-MS/MS profiling showed that the acetyllysine sites of H-NS and K120 are indispensable for its DNA-binding ability. Acetylation of K120 leads to a low binding affinity for DNA and enhances T3/T6SS expression. Furthermore, acetylation of K120 impairs the AT-rich DNA recognition ability of H-NS. In addition, lysine acetylation in H-NS modulates in vivo bacterial virulence. These findings reveal the mechanism underlying H-NS PTMs and propose a novel mechanism by which bacteria counteract the xenogeneic silencing of H-NS.

NITR12+ NK Cells Release Perforin to Mediate IgMhi B Cell Killing in Turbot (Scophthalmus maximus).

B lymphocytes engaged in humoral immunity play a critical role in combating pathogenic infections; however, the mechanisms of NK cells in regulating the responses of B cells remain largely unknown. In the present study, we established an Edwardsiella piscicida infection model in turbot (Scophthalmus maximus) and found that the production of IgM was decreased. Meanwhile, through establishing the head kidney-derived lymphocyte infection model, we revealed that the impairment of IgMhi B cells was associated with bacterial infection-induced perforin production. Interestingly, we reveal that perforin production in NK cells is tightly regulated by an inhibitory novel immune-type receptor, NITR12. Moreover, we confirm that inhibiting NITR12 can result in elevated perforin production, engaging the impairment of IgMhi B cells. Taken together, these findings demonstrate an innovative strategy of NK cells in mediating B lymphocyte killing in turbot and suggest that relieving NK cells through NITR12 might be the target for the development of efficacious vaccines.

Poly(I:C) induces anti-inflammatory response against secondary LPS challenge in zebrafish larvae.

Poly(I:C) is known as an agonist of the TLR3 receptor which could prime inflammation and elicit the host immune response, which is widely applied as adjuvant or antivirus treatment. However, the negative effects of poly(I:C) on regulating immune response to protect the host from inflammatory diseases remain largely unknown. Here, we establish an in vivo model to pre-treat zebrafish larvae with poly(I:C) at 2 dpf, then challenge them with LPS at 6 dpf, and find that poly(I:C) training could significantly alleviate the LPS challenge-induced septic shock and inflammatory phenotypes. Moreover, the poly(I:C)-trained larvae exhibit decreased number of macrophages, but not neutrophils, after secondary LPS challenge. Furthermore, training the larvae with poly(I:C) could elevate the transcripts of mTOR signaling and heighten the H3K4me3-mediated epigenetic modifications. And interestingly, we find that inhibiting the H3K4me3 modification, rather than mTOR signaling, could recover the number of macrophages in poly(I:C)-trained larvae, which is consistent with the observations of inflammatory phenotypes. Taken together, these results suggest that poly(I:C) training could induce epigenetic rewiring to mediate the anti-inflammatory response against secondary LPS challenge-induced septic shock through decreasing macrophages' number in vivo, which might expand our understanding of poly(I:C) in regulating fish immune response.

An aluminium adjuvant compound with ginseng stem leaf saponins enhances the potency of inactivated Pseudomonas plecoglossicida vaccine in large yellow croaker (Larimichthys crocea).

Large yellow croaker (Larimichthys crocea) farm industry in China suffered from huge economic loss caused by Pseudomonas plecoglossicida infection. Due to multi-antibiotic resistance, efficient vaccines are urgent to be developed to combat this pathogen. In this study, an inactivated vaccine was developed with an aluminium adjuvant (Alum) plus ginseng stem and leaf saponins (GSLS). As a result, the relative percentage survival (RPS) against P. plecoglossicida was up to 67.8 %. Comparatively, RPS of groups that vaccinated with only inactivated vaccine and vaccine containing Alum or Montanide™ 763A as adjuvant were 21.8 %, 32.2 % and 62.1 %, respectively. Assays for total serum protein and serum lysozyme activity in group vaccinated with inactivated vaccine plus Alum + GSLS adjuvant were significantly higher than that in control group. Moreover, specific antibody in serum elicited a rapid and persistent level. According to the expression of some immune related genes, inactivated vaccine plus Alum + GSLS adjuvant induced a stronger cellular immune response which was vital to defend against P. plecoglossicida. In conclusion, our study demonstrated that the compound Alum and GSLS adjuvant is a potential adjuvant system to develop LYC vaccine.

A bacterial ghost vaccine against Aeromonas salmonicida infection in turbot (Scophthalmus maximus).

Aeromonas salmonicida is one of the most prevalent pathogens that causes huge economic losses to aquaculture. Effective vaccination is the first choice for preventing infection. Bacterial ghost (BG), an empty bacterial shell devoid of cytoplasm, is a promising vaccine antigen with distinct advantages. Herein, we established strategies for producing a substantial yield of A. salmonicida ghost (ASG) and investigated the immune-protective properties of it. As a result, 2.84 mg/ml NaOH was discovered to be capable of inducing considerable amounts of ASG. Furthermore, the ASG vaccine elicited adaptive immunity in turbots after rapid activation of innate immunity. Even though formalin-killed cells (FKC) produced a few more antibodies than ASG, ASG ultimately provided a much stronger immune protection effect because it strengthened cellular immunity, with a relative percentage survival (RPS) of 50.1 % compared to FKC. These findings demonstrated that ASG effectively activated cell-mediated immunity, which helped get rid of microorganisms inside cells. Therefore, this study presented novel perspectives for future research on furunculosis vaccine products based on ASG as an antigen.

Single-Cell Transcriptomic Analysis Reveals Neutrophil as Orchestrator during ß-Glucan-Induced Trained Immunity in a Teleost Fish.

Trained immunity defines long-term memory of innate immunity based on transcriptional, epigenetic, and metabolic modifications of myeloid cells, which are characterized by elevated proinflammatory responses toward homologous or heterologous secondary stimuli in mammals. However, the evidence of trained immunity-associated immune cells and its molecular mechanism in teleost fish remains largely unknown. In this study, we established a trained immunity activation model in turbot (Scophthalmus maximus) and found that administration with ß-glucan induces protection against a bacterial infection. Through single-cell RNA sequencing to annotate 14 clusters of innate and adaptive immune cells, as well as two clusters of blood cells, from head kidney and spleen, respectively, we characterized that neutrophil displays cardinal features of trained immunity by analyzing the expression abundance of trained immunity database-related genes at the single-cell level. Subsequently, through establishing an in vivo training and in vitro neutrophil challenge model, we found that the trained neutrophils exhibit a significant elevation of the IL-1R signaling pathway after Edwardsiella piscicida infection. Furthermore, inhibition of neutrophil's IL-1R signaling pathway through anakinra treatment impaired the heightened production of reactive oxygen, nitrogen species, lactate, as well as the neutrophil extracellular traps formation and bacterial killing ability. Taken together, these findings characterized neutrophil as the orchestrator to express features of trained immunity, and revealed that the IL-1R signaling pathway plays a critical role in induction of trained immunity for bacterial clearance in teleost fish.

Yeast transcriptional device libraries enable precise synthesis of value-added chemicals from methanol.

Natural methylotrophs are attractive methanol utilization hosts, but lack flexible expression tools. In this study, we developed yeast transcriptional device libraries for precise synthesis of value-added chemicals from methanol. We synthesized transcriptional devices by fusing bacterial DNA-binding proteins (DBPs) with yeast transactivation domains, and linking bacterial binding sequences (BSs) with the yeast core promoter. Three DBP-BS pairs showed good activity when working with transactivation domains and the core promoter of PAOX1 in the methylotrophic yeast, Pichia pastoris. Fine-tuning of the tandem BSs, spacers and differentiated input promoters further enabled a constitutive transcriptional device library (cTRDL) composed of 126 transcriptional devices with an expression strength of 16-520% and an inducible TRDL (iTRDL) composed of 162 methanol-inducible transcriptional devices with an expression strength of 30-500%, compared with PAOX1. Selected devices from iTRDL were adapted to the dihydromonacolin L biosynthetic pathway by orthogonal experimental design, reaching 5.5-fold the production from the PAOX1-driven pathway. The full factorial design of the selected devices from the cTRDL was adapted to the downstream pathway of dihydromonacolin L to monacolin J. Monacolin J production from methanol reached 3.0-fold the production from the PAOX1-driven pathway. Our engineered toolsets ensured multilevel pathway control of chemical synthesis in methylotrophic yeasts.

Xenogeneic nucleoid-associated EnrR thwarts H-NS silencing of bacterial virulence with unique DNA binding.

Type III and type VI secretion systems (T3/T6SS) are encoded in horizontally acquired genomic islands (GIs) that play crucial roles in evolution and virulence in bacterial pathogens. T3/T6SS expression is subjected to tight control by the host xenogeneic silencer H-NS, but how this mechanism is counteracted remains to be illuminated. Here, we report that xenogeneic nucleoid-associated protein EnrR encoded in a GI is essential for virulence in pathogenic bacteria Edwardsiella and Salmonella. We showed that EnrR plays critical roles in T3/T6SS expression in these bacteria. Various biochemical and genetic analyses demonstrated that EnrR binds and derepresses the promoter of esrB, the critical regulator of T3/T6SS, to promote their expression by competing with H-NS. Additionally, EnrR targets AT-rich regions, globally modulates the expression of ∼363 genes and is involved in various cellular processes. Crystal structures of EnrR in complex with a specific AT-rich palindromic DNA revealed a new DNA-binding mode that involves conserved HTH-mediated interactions with the major groove and contacts of its N-terminal extension to the minor groove in the symmetry-related duplex. Collectively, these data demonstrate that EnrR is a virulence activator that can antagonize H-NS, highlighting a unique mechanism by which bacterial xenogeneic regulators recognize and regulate foreign DNA.

FabR senses long-chain unsaturated fatty acids to control virulence in pathogen Edwardsiella piscicida.

Long-chain unsaturated fatty acids (UFAs) can serve as nutrient sources or building blocks for bacterial membranes. However, little is known about how UFAs may be incorporated into the virulence programs of pathogens. A previous investigation identified FabR as a positive regulator of virulence gene expression in Edwardsiella piscicida. Here, chromatin immunoprecipitation-sequencing coupled with RNA-seq analyses revealed that 10 genes were under the direct control of FabR, including fabA, fabB, and cfa, which modulate the composition of UFAs. The binding of FabR to its target DNA was facilitated by oleoyl-CoA and inhibited by stearoyl-CoA. In addition, analyses of enzyme mobility shift assay and DNase I footprinting with wild-type and a null mutant (F131A) of FabR demonstrated crucial roles of FabR in binding to the promoters of fabA, fabB, and cfa. Moreover, FabR also binds to the promoter region of the virulence regulator esrB for its activation, facilitating the expression of the type III secretion system (T3SS) in response to UFAs. Furthermore, FabR coordinated with RpoS to modulate the expression of T3SS. Collectively, our results elucidate the molecular machinery of FabR regulating bacterial fatty acid composition and virulence in enteric pathogens, further expanding our knowledge of its crucial role in host-pathogen interactions.

Identification of a novel transcriptional regulator, CorR, for copper stress response in Edwardsiella piscicida.

Copper plays a vital role in the host-pathogen interface, potentially making components of the bacterial copper response suitable targets for the development of innovative antimicrobial strategies. The anti-copper arsenal of intracellular pathogens has expanded as an adaptation to survive copper toxicity in order to escape intracellular killing by the host immune system. Herein, we employed transposon insertion sequencing to investigate the genetic mechanisms underlying the survival of Edwardsiella piscicida under copper stress. A novel transcriptional regulator, ETAE_2324 (named CorR), was identified to participate in the response to copper ions by controlling the expression of copA, the core component of cytoplasmic copper homeostasis. Furthermore, CorR regulated the expression of virulent determinant eseB, influencing the in vivo colonization of E. piscicida. Collectively, our results contribute to the comprehension of the underlying mechanism of the adaption of intracellular pathogens to copper stress during bacterial infections.IMPORTANCECopper ions play a pivotal role in the interaction between bacteria and the host during infection. The host's innate immune system employs copper ions for their bactericidal properties, thereby making bacterial copper tolerance a crucial determinant of virulence. Edwardsiella piscicida, a significant marine pathogen, has caused substantial losses in the global aquaculture industry. To comprehensively investigate how E. piscicida responds to copper stress, we utilized transposon insertion sequencing to explore genes associated with copper tolerance in culture media containing different concentrations of copper ions. A novel transcriptional regulator, CorR, was identified to respond to copper ions and regulates the expression of crucial components of copper homeostasis CopA, along with the essential virulence factor EseB. These findings offer valuable insights into the underlying mechanisms that govern bacterial copper tolerance and present novel perspectives for the development of vaccines and therapeutic strategies targeting E. piscicida.

Characterization and pathogenicity analysis of a newly isolated strain of infectious hematopoietic necrosis virus.

Rainbow trout is one of the fastest-growing aquaculture species and infectious hematopoietic necrosis virus (IHNV) is endemic throughout almost all rainbow trout farms in China nowadays. In this study, IHNV GS21 was identified as the causative pathogen, which resulted in massive mortality of rainbow trout occurring in northwest China. GS21 isolate was propagated in Chinook salmon embryonic cell line (CHSE-214) and induced apparent cytopathic effects (CPE) at 3 days post-infection (dpi). Phylogenetic analysis revealed that GS21 isolate was clustered with other reported Chinese isolates within the J genogroup. Moreover, the complete cDNA sequence of GS21 isolate was obtained and it possesses more than 98 % of ANI values and 89 % of DDH values with other Chinese IHNV isolates. The detailed sequence analysis of G gene revealed the distinct amino acid substitutions of G230, G252, G270, and I277 in GS21 isolate. Furthermore, the artificially infected rainbow trout exhibited similar clinical disease symptoms as natural infection did. The cumulative mortality infected by GS21 isolate of 104 PFU/mL reached 93 % at approximately 13.5 °C. Additionally, viral loads in tissues increased first and declined then as well as the expression of immune-associated genes. Collectively, our results characterized a novel IHNV GS21 isolate that can lead to massive mortality in juvenile rainbow trout and provided a basis to define the pathogenic characteristics and evolutionary relationship of IHNV and host immune response against IHNV infection.

Preparation of Buffered Nano-Submicron Hierarchical Structure Hollow SiOx @C Anodes for Lithium-Ion Battery Materials with Carboxymethyl Chitosan.

Silicon-based materials are among the most promising anode materials for next-generation lithium-ion batteries. However, the volume expansion and poor conductivity of silicon-based materials during the charge and discharge process seriously hinder their practical application in the field of anodes. Here, we choose carboxymethyl chitosan (CMCS) as the carbon source coating and binding on the surface of nano silicon and hollow silicon dioxide (H-SiO2 ) to form a hierarchical buffered structure of nano-hollow SiOx @C. The hollow H-SiO2 can alleviate the volume expansion of nano silicon during the lithiation process under continuous cycling. Meanwhile, the carbon layer carbonized by CMCS containing N-doping further regulates the silicon's expansion and improves the conductivity of the active materials. The as- prepared SiOx @C material exhibits an initial discharge capacity of 985.4 mAh g-1 with the decay rate of 0.27 % per cycle in 150 cycles under the current density of 0.2 A g-1 . It is proved that the hierarchical buffer structure nano-hollow SiOx @C anode material has practical application potential.

Characterization of ccl20a.3 and ccl20l as gene markers for Th17 cell in turbot.

T-helper 17 lymphocytes (Th17) are the most common inflammatory cells identified in mammals. However, the identification of Th17 cells and the clarification of their function in teleost fish remain largely unknown. In this study, we took advantage of the single-cell RNA sequencing-based immune cell atlas that was identified in turbot (Scophthalmus maximus), and revealed two chemokine-related genes, ccl20a.3 and ccl20l, that were specifically expressed in Th17 cells. Moreover, through immuno-fluorescence analysis, we found that CCL20a.3 or CCL20l was co-expressed with the classical makers in Th17 cells, including IL17a/f1 and IL22. Furthermore, through a Th17 lineage-specific transcription factor RORc inhibitor GSK805 treatment, we found that the expression of ccl20a.3 and ccl20l was significantly impaired, compared with other T cell markers. Besides, we also found that ccl20a.3 and ccl20l exhibited the same dynamic response with the classical markers that were identified in Th17 cells during bacterial infection. Taken together, these results provide potential gene markers for better understanding of the dynamic immune responses of Th17 cells in teleost fish.

Characterization of T-cell receptors and immunoglobulin heavy chains loci and identification of T/B cell clusters in teleost.

Bacterial disease is one of the important factors leading to economic losses in the turbot (Scophthalmus maximus) cultivation industry. T lymphocytes are major components of cellular immunity, whereas B lymphocytes produce immunoglobulins (Ig) that are key elements of humoral immune responses against infection. However, the genomic organization of genes encoding T-cell receptors (TCR) and immunoglobulin heavy chains (IgHs) in turbot remains largely unknown. In this study, abundant full-length transcripts of TCRs and IgHs were sequenced by Isoform-sequencing (Iso-seq), and we investigated and annotated the V, D, J and C gene loci of TCRα, TCRß, IgT, IgM and IgD in turbot. Furthermore, through single-cell RNA sequencing (scRNA-seq) of blood leukocytes, we confirmed that these identified TCRs and IgHs were highly expressed in T/B cell clusters, respectively. Meanwhile, we also identified the IgM+IgD+ B and IgT+ B cells with differential gene expression profiles and potential functions. Taken together, our results provide a comprehensive understanding of TCRs and IgHs loci in turbot, which will contribute to evolutionary and functional characterization of T and B lymphocytes in teleost.

Pyroptosis Mediates Neutrophil Extracellular Trap Formation during Bacterial Infection in Zebrafish.

The formation of neutrophil extracellular trap (NET) is a critical host defense when neutrophils migrate to infection sites. Pyroptosis is a newly identified programmed cell death, which is tightly regulated by inflammasome activation. However, the mechanism of pyroptotic signaling participating in NET production remains to be elucidated. In this study, the zebrafish larvae otic vesicle microinjection model was used to infect larvae with hemolysin-overexpressing Edwardsiella piscicida (EthA+), and a rapid migration of neutrophils to infection sites was observed. Intriguingly, EthA+ infection effectively induced significant neutrophil membrane rupture in vivo, which was dependent on caspase-B (caspy2) and gasdermin Eb (GSDMEb) but not caspase-A or gasdermin Ea. Specifically, the EthA+ E. piscicida infection induced pyroptosis along with NETosis in vitro, and depletion of either caspy2 or GSDMEb impaired NET formation in vivo. Consequently, inhibition of the caspy2-GSDMEb axis-gated NETosis impaired bacterial clearance in vivo. Altogether, these data provide evidence that teleost fish innate immune cells, including neutrophils, express features of pyroptosis that are critical for NETosis in teleost innate immunity.

The c-di-GMP signalling component YfiR regulates multiple bacterial phenotypes and virulence in Pseudomonas plecoglossicida.

AIMS: Pseudomonas plecoglossicida (P. plecoglossicida) is the causative agent of visceral granulomas disease in large yellow croaker (Larimichthys crocea) and it causes severe economic loss to its industry. Biofilm formation, related to intracellular cyclic bis (3'-5') diguanylic acid (c-di-GMP) levels, is essential for the lifestyle of P. plecoglossicida. This research aims to investigate the role of YfiR-a key regulator of the diguanylate cyclase YfiN to regulate c-di-GMP levels and reveal its regulatory function of bacterial virulence expression in P. plecoglossicida. METHODS AND RESULTS: A genetic analysis was carried out to identify the yfiBNR operon for c-di-GMP regulation in P. plecoglossicida. Then, we constructed a yfiR mutant and observed increased c-di-GMP levels, enhanced biofilm formation, increased exopolysaccharides, and diminished swimming and swarming motility in this strain. Moreover, through establishing a yolk sac microinjection infection model in zebrafish larvae, an attenuated phenotype of yfiR mutant that manifested as restored survival and lower bacterial colonization was found. CONCLUSIONS: YfiR is the key regulator of virulence in P. plecoglossicida, which contributes to c-di-GMP level, biofilm formation, exopolysaccharides production, swimming, swarming motility, and bacterial colonization in zebrafish model.

Identification of determinants for entering into a viable but nonculturable state in Vibrio alginolyticus by Tn-seq.

The viable but nonculturable (VBNC) state is a dormant state of nonsporulating bacteria that enhances survival in adverse environments. Systematic genome-wide research on the genetic basis of VBNC formation is warranted. In this study, we demonstrated that the marine bacterium Vibrio alginolyticus lost culturability but remained viable and entered into the VBNC state when exposed to low nutrient concentrations for prolonged periods of time. Using transposon-insertion sequencing (Tn-seq), we identified 635 determinants governing the formation of the VBNC state, including 322 genes with defective effects on VBNC formation and 313 genes contributing to entry into the VBNC state. Tn-seq analysis revealed that genes involved in various metabolic pathways were shown to have an inhibitory effect on VBNC formation, while genes related to chemotaxis or folate biosynthesis promoted entry into the VBNC state. Moreover, the effects of these genes on the formation of VBNC were validated with the growth of deletion mutants of eight selected genes under nutrient-limited conditions. Interestingly, fleQ and pyrI were identified as essential for entry into the VBNC state, and they affected the formation of the VBNC state independent of RpoE or ToxR regulation. Collectively, these results provide new insights into the mechanism of VBNC formation. KEY POINTS: • Vibrio alginolyticus has the ability to enter into the VBNC state under low nutrient conditions at low temperature. • The 635 determinants for entry into the VBNC state were systematically identified by transposon-insertion sequencing. • PyrI and FleQ were validated to play significant roles in the formation of the VBNC state.

Binding site profiles and N-terminal minor groove interactions of the master quorum-sensing regulator LuxR enable flexible control of gene activation and repression.

LuxR is a TetR family master quorum sensing (QS) regulator activating or repressing expression of hundreds of genes that control collective behaviors in Vibrios with underlying mechanism unknown. To illuminate how this regulator controls expression of various target genes, we applied ChIP-seq and DNase I-seq technologies. Vibrio alginolyticus LuxR controls expression of ∼280 genes that contain either symmetric palindrome (repDNA) or asymmetric (actDNA) binding motifs with different binding profiles. The median number of LuxR binding sites for activated genes are nearly double for that of repressed genes. Crystal structures of LuxR in complex with the respective repDNA and actDNA motifs revealed a new mode of LuxR DNA binding that involves contacts of its N-terminal extension to the minor groove. The N-terminal contacts mediated by Arginine-9 and Arginine-11 differ when LuxR binds to repDNA vs actDNA, leading to higher binding affinity at repressed targets. Moreover, modification of LuxR binding sites, binding profiles, and N-terminal extension have important consequences on QS-regulated phenotypes. These results facilitate fundamental understanding of the high flexibility of mechanisms of LuxR control of gene activation and repression in Vibrio QS, which may facilitate to design QS inhibiting chemicals that interfere with LuxR regulation to effectively control pathogens.

Chemically Induced Activity Recovery of Isolated Lithium in Anode-free Lithium Metal Batteries.

The anode-free lithium metal battery is considered to be an excellent candidate for the new generation energy storage system because of its higher energy density and safety than the traditional lithium metal battery. However, the continuous generation of SEI or isolated Li hinders its practical application. In general, the isolated Li is considered electrochemically inactive because it loses electrical connection with the current collector. Here we show an abnormal phenomenon that the lost capacity appears to be recovered after cycles when the isolated Li reconnects with a deposited Li metal layer. The isolated Li reconnection is ascribed to the chemical induction of the block copolymer coating. The migration of Li+ is affected by the electron delocalization and the electron cloud density of the polymer, which determine the conversion direction of Li+. Based on the mechanism, we propose a strategy to slow down the capacity decay of the anode-free lithium metal battery.

Mechanism of Escherichia coli Lethality Caused by Overexpression of flhDC, the Flagellar Master Regulator Genes, as Revealed by Transcriptome Analysis.

The flhDC operon of Escherichia coli encodes a transcription factor that initiates flagella synthesis, elevates flagella construction and enhances cell motility, which all are energetically costly and highly regulated processes. In this study, we found that overexpression of flhDC genes from a strong regulatable pN15E6 plasmid could inhibit the growth of E. coli host cells and even eventually cause death. We used transcriptome analysis to investigate the mechanism of flhDC overexpression lethal to host bacteria. The results showed that a total of 568 differentially expressed genes (DEGs), including 378 up-regulated genes and 190 down-regulated genes were detected when the flhDC genes were over-expressed. Functional enrichment analysis results showed that the DEGs are related to a series of crucial biomolecular processes, including flagella synthesis, oxidative phosphorylation and pentose phosphate pathways, etc. We then examined, using RT-qPCR, the expression of key genes of the oxidative phosphorylation pathway at different time points after induction. Results showed that their expression increased in the early stage and decreased afterward, which was suggested to be the result of feedback on the overproduction of ROS, a strong side effect product of the elevated oxidative phosphorylation process. To further verify the level of ROS output, flhDC over-expressed bacteria cells were stained with DCHF-DA and a fluorescence signal was detected using flow cytometry. Results showed that the level of ROS output was higher in cells with over-expressed flhDC than in normal controls. Besides, we found upregulation of other genes (recN and zwf) that respond to ROS damage. This leads to the conclusion that the bacterial death led by the overexpression of flhDC genes is caused by damage from ROS overproduction, which leaked from the oxidative phosphorylation pathway.