OBJECTIVE: Pseudomonas plecoglossicida belongs to the Pseudomonas putida group and is a common aquatic pathogen that induces visceral lesions in fish. However, it has never been previously isolated from human specimen and associated with human infections. In the study, we first investigated the pathogenicity of Pseudomonas plecoglossicida strain \"SXY\" isolated from a child with infectious pneumonia.
METHODS: Using 16S rRNA sequencing, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis, and unique biochemical phenotypes, we isolated and identified Pseudomonas plecoglossicida in clinical practice, a highly suspicious pneumonia-related pathogen based on bacteriological examinations and clinical manifestations. Its pathogenicity was assessed and compared with that of Pseudomonas putida clinical strain \"ECL\" (a recognized pathogen in the Pseudomonas putida group) by a series of in vitro pathogenicity tests (including the growth capacity assay at 37 °C, the lung leukocyte-killing and inflammatory factor release assay, and the whole blood-killing, serum-killing and complement sensitivity assay).
RESULTS: All tests demonstrated its ability to cause colonization, infection, and inflammation in the lungs. However, the pathogenicity and risk of bloodstream infection of Pseudomonas plecoglossicida strain \"SXY\" were limited and weaker than those of Pseudomonas putida strain \"ECL\". Notably, Pseudomonas plecoglossicida could be incorrectly identified as Pseudomonas putida, based on the biochemical identification of VITEK-2, potentially leading to a high rate of missing infections.
CONCLUSIONS: Pseudomonas plecoglossicida is a potential and neglected pneumonia pathogen.

Cadmium (Cd) in rice is a significant concern for its quality and safety. Currently, there is a crucial need to develop cost-effective and efficient ways to remove Cd or re-utilize Cd-contaminated rice. The food additive sodium erythorbate is produced via 2-ketogluconic acid (2KGA) fermentation by Pseudomonas plecoglossicida and lactonization using starch-rich raw materials, such as rice. We aimed to determine whether cadmium-contaminated rice can be used to produce sodium erythorbate. To achieve this aim, the migration of cadmium during the production of sodium erythorbate from Cd-contaminated rice was studied. Five rice varieties with different Cd contents from 0.10 to 0.68 mg/kg were used as raw materials. The results indicated the presence of Cd in rice and CaCO3 did not have a notable impact on the fermentation performance of 2KGA. The acidification of 2KGA fermentation broth, the addition of K4Fe(CN)6·3H2O and ZnSO4, and 2KGA purification using cation exchange effectively removed >98% of the Cd in the fermentation broth, but the 2KGA yield remained high at approximately 94%. The sodium erythorbate synthesized from Cd-contaminated rice was of high quality and free from Cd, meeting the requirements of the Chinese National Standard, GB 1886.28-2016. The study provided a safe and effective strategy for comprehensively utilizing Cd-contaminated rice to produce high value-added food additive.

Pseudomonas plecoglossicida is one of most important pathogenic bacterial species in large yellow croaker and several other commercially valuable fish species. In our previous study, a GacS deficient mutant (ΔgacS) was constructed and its virulence showed substantially attenuated. In present study, the safety, immunogenicity and protective effect of the ΔgacS were evaluated in large yellow croaker as a live-attenuated vaccine candidate. It was shown that the ΔgacS strain exhibited good safety to large yellow croaker and there was no mortality or clinical symptoms observed in all fish that infected by ΔgacS strain with the doses range from 2 × 105～107 CFU per fish via intraperitoneal injection (IP) or immersion (IM), and almost all bacteria were cleaned up in the spleen of the fish at 14-day post infection. Specific antibodies could be detected at 7-day and 14-day post infection by direct agglutination method, and the valences of antibodies and bactericidal activities of the serum were significant increased with vaccination doses and vaccination time. Moreover, the expressions of some molecules and cytokines involved in specific immune responses were detected in the ΔgacS strain immunization group and control group. After challenged by the wild-type (WT) strain XSDHY-P, the relative percentage survival (RPS) showed highly correlated with the immunized dosage regardless of vaccination methods. It showed that the RPS of the IP groups were 39.47 %, 57.89 %, 71.05 % with the immune dosage in a descending order, respectively, and the RPS of the IM groups were 26.31 %, 36.84 %, 76.31 % with the immune dosage in a descending order, respectively. In summary, the ΔgacS strain exhibited safety and good protective effect to large yellow croaker and was a potential live vaccine candidate.

Naphthalene is a persistent environmental pollutant for its potential teratogenic, carcinogenic and mutagenic effects. In this study, 10 strains of bacteria capable of degrading naphthalene were isolated from crude-oil contaminated soil. Among them, Pseudomonas plecoglossicida 2P exhibited prominent growth with 1000 mg/L naphthalene as the sole carbon source and degraded 94.15% of naphthalene in 36 h. Whole genome sequencing analysis showed that P. plecoglossicida 2P had a total of 22 genes related to naphthalene degradation, of which 8 genes were related to the salicylic acid pathway only, 5 genes were related to the phthalic acid pathway only, 8 genes were common in both the salicylic acid and phthalic acid pathways, and 1 gene was related to the gentisic acid pathway. P. plecoglossicida 2P was applied in a two-phase partition bioreactor (TPPB) to degrade naphthalene in wastewater. The optimal operating conditions of the reactor were obtained through response surface optimization: initial naphthalene concentration (C0) =1600 mg/L, bacterial liquid concentration (OD600) = 1.3, and polymer-to-wastewater mass ratio (PWR) = 2%. Under these conditions, the naphthalene degradation rate was 98.36% at 24 h. The degradation kinetics were fitted using the Haldane equation with a high coefficient of determination (R2=0.94). The present study laid foundations for naphthalene degradation mechanism of genus Pseudomonas and its potential application in TPPB.

The COMMD (Copper Metabolism gene MURR1 Domain) gene family consists of 10 members, which are involved in various biological processes such as copper and sodium transport, NF-κB activity and cell cycle progression. However, the study of COMMD gene family in large yellow croaker (Larimichthys crocea) is largely unknown. In this study, 10 COMMD gene family members (named LcCOMMDs) were successfully identified from large yellow croaker. The results showed that there were differences in the number of LcCOMMDs exons at the level of gene structure, which reflected that they had adjusted and changed accordingly in the process of evolution to adapt to the environment and achieved functional diversification. Through phylogenetic analysis, we found that the LcCOMMDs was highly conserved, indicating their important functions in organisms. It was worth noting that the expression levels of LcCOMMD1, LcCOMMD2, LcCOMMD3, LcCOMMD5 and LcCOMMD10 in the spleen changed significantly after bacterial stress, which suggested that these genes might be involved in the regulation of innate immune response. In addition, the expression levels of LcCOMMD1, LcCOMMD2, LcCOMMD3, LcCOMMD5, LcCOMMD7, LcCOMMD8, LcCOMMD9 and LcCOMMD10 changed significantly after hypoxia exposure, which further proved the role of LcCOMMDs in immune function. In summary, this study not only revealed the important role of COMMD genes in the innate immune response of large yellow croaker, but also provided valuable information for further understanding the regulatory mechanism of COMMD gene family under different conditions.

Pseudomonas plecoglossicida, a gram-negative bacterium, is the main pathogen of visceral white-point disease in marine fish, responsible for substantial economic losses in the aquaculture industry. The FliL protein, involved in torque production of the bacterial flagella motor, is essential for the pathogenicity of a variety of bacteria. In the current study, the fliL gene deletion strain (ΔfliL), fliL gene complement strain (C-ΔfliL), and wild-type strain (NZBD9) were compared to explore the influence of the fliL gene on P. plecoglossicida pathogenicity and its role in host immune response. Results showed that fliL gene deletion increased the survival rate (50%) and reduced white spot disease progression in the hybrid groupers. Moreover, compared to the NZBD9 strain, the ΔfliL strain was consistently associated with lower bacterial loads in the grouper spleen, head kidney, liver, and intestine, coupled with reduced tissue damage. Transcriptomic analysis identified 2 238 differentially expressed genes (DEGs) in the spleens of fish infected with the ΔfliL strain compared to the NZBD9 strain. Based on Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis, the DEGs were significantly enriched in seven immune system-associated pathways and three signaling molecule and interaction pathways. Upon infection with the ΔfliL strain, the toll-like receptor (TLR) signaling pathway was activated in the hybrid groupers, leading to the activation of transcription factors (NF-κB and AP1) and cytokines. The expression levels of proinflammatory cytokine-related genes IL-1β, IL-12B, and IL-6 and chemokine-related genes CXCL9, CXCL10, and CCL4 were significantly up-regulated. In conclusion, the fliL gene markedly influenced the pathogenicity of P. plecoglossicida infection in the hybrid groupers. Notably, deletion of fliL gene in P. plecoglossicida induced a robust immune response in the groupers, promoting defense against and elimination of pathogens via an inflammatory response involving multiple cytokines.

Pseudomonas plecoglossicida is a vital pathogen that poses a substantial risk to aquaculture. Small RNAs (sRNAs) are non-coding regulatory molecules capable of sensing environmental changes and modulating virulence-associated signaling pathways, such as the assembly of flagella. However, the relevant researches on P. plecoglossicida are an urgent need. Here, we report a novel sRNA, sRNA562, which has potential to regulate the post-transcriptional of fliP, a key component of the lateral flagellar type III secretion system. In this study, the effects of sRNA562 on the virulence of P. plecoglossicida and its role in regulating the pathogenic process were investigated through the use of a constructed sRNA562 deletion strain. The deletion of sRNA562 resulted in an up-regulation of fliP in P. plecoglossicida, and leading to increased swarming motility and enhanced the ability of biofilm formation, adhesion and chemotaxis. Subsequent artificial infection experiment demonstrated that the deletion of sRNA562 increased the virulence of P. plecoglossicida towards hybrid grouper, as evidenced by a reduction in survival rate, elevation of tissue bacterial load, and the exacerbation of histopathological damage. Further studies have found that the deletion of sRNA562 lead to an up-regulation of fliP expression during hybrid grouper infection, thereby enhancing bacterial swarming ability and ultimately heightening pathogenicity, leading to a dysregulated host response to infection, tissue damage and eventually death. Our work revealed a sRNA that exerts negative regulation on the expression of lateral flagella in P. plecoglossicida, thereby impacting its virulence. These findings provide a new perspective on the virulence regulation mechanism of P. plecoglossicida, contributing to a more comprehensive understanding in the field of pathogenicity research.

The suppressor of cytokine signaling (SOCS) gene family is a group of genes involved in the negative regulation of cytokine signal transduction. The members of this family play a crucial role in regulating immune and inflammatory processes. However, comprehensive investigations of these genes have not yet been conducted in the economically significant fish large yellow croaker (Larimichthys crocea). In this study, a total of 13 SOCS genes (LcSOCS1a, LcSOCS1b, LcSOCS2, LcSOCS3a, LcSOCS3b, LcSOCS4, LcSOCS5a, LcSOCS5b, LcSOCS6, LcSOCS7a, LcSOCS7b, LcCISHa and LcCISHb) were identified and analyzed in L. crocea. The phylogenetic tree revealed a high conservation of SOCS genes in evolution, and the gene structure and motif analysis indicated a high similarity in the structure of LcSOCSs in the same subfamily. In addition, the expression patterns of LcSOCSs showed that LcSOCS1b was significantly down-regulated in all time under acute hypoxia stress, but it was markedly up-regulated throughout the entire process after P. plecoglossicida infection, revealing its different immune effects to two stresses. Besides, LcSOCS2a, LcSOCS6 and LcSOCS7a only participated in acute hypoxic stress, while LcSOCS5a was more sensitive to P. plecoglossicida infection. In summary, these results indicated that SOCS genes were involved in stress responses to both biological and non-biological stimuli, setting the foundation for deeper study on the functions of SOCS genes.

The visceral white nodules disease in the internal organs of Larimichthys crocea has caused significant harm in the aquaculture of this species, with Pseudomonas plecoglossicida considered one of the core pathogens causing this disease. In this study, we designed three pairs of specific nested PCR primers targeting the sctU gene of P. plecoglossicida, a crucial component of the Type III secretion system (T3SS), which is instrumental in bacterial pathogenesis and virulence. Through the optimization of PCR reaction conditions, specificity testing, and sensitivity determination, a method was established for the accurate detection of P. plecoglossicida. This method yielded single amplification products, exhibited a false positive rate of zero for reference bacteria, and achieved a detection sensitivity of a minimum of 2.62 copies/reaction for the target sequence. Using the detection method, we conducted analyses on the diseased populations of L. crocea, involving a total of 64 screened fishes along the southeast coast of China from 2021 to 2023. The results revealed that the infection rate of P. plecoglossicida in diseased L. crocea exceeded over 90% in March and April, while in other months, the maximum recorded infection rate was merely 10%. The detection method developed in this study shows potential for early warning and routine monitoring of visceral white nodules disease in the internal organs of species such as L. crocea.

Pseudomonas plecoglossicida, the causative agent of Visceral White Spot Disease, poses substantial risks to large yellow croaker (Larimichthys crocea) aquaculture. Previous genome-wide association studies (GWAS), directed towards elucidating the resistance mechanisms of large yellow croaker against this affliction, suggested that the transmembrane protein 208 (named Lctmem208) may confer a potential advantage. TMEM proteins, particularly TMEM208 located in the endoplasmic reticulum, plays significant roles in autophagy, ER stress, and dynamics of cancer cell. However, research on TMEM\'s function in teleost fish immunity remains sparse, highlighting a need for further study. This study embarks on a comprehensive examination of LcTmem208, encompassing cloning, molecular characterization, and its dynamics in immune function in response to Pseudomonas plecoglossicida infection. Our findings reveal that LcTmem208 is highly conserved across teleost species, exhibiting pronounced expression in immune-relevant tissues, which escalates significantly upon pathogenic challenge. Transcriptome analysis subsequent to LcTmem208 overexpression in kidney cells unveiled its pivotal role in modulating immune-responsive processes, notably the p53 signaling pathway and cytokine-mediated interactions. Enhanced phagocytic activity in macrophages overexpressing LcTmem208 underscores its importance in innate immunity. Taken together, this is the first time reported the critical involvement of LcTmem208 in regulating innate immune responses of defensing P. plecoglossicida, thereby offering valuable insights into teleost fish immunity and potential strategies for the selective breeding of disease-resistant strains of large yellow croaker in aquaculture practices.