Taurine promotes Oreochromis niloticus survival against Edwardsiella tarda infection

α-Ketoglutarate downregulates thiosulphate metabolism to enhance antibiotic killing

Potentiation of the effects of currently available antibiotics is urgently required to tackle the rising antibiotics resistance. The pyruvate (P) cycle has been shown to play a critical role in mediating aminoglycoside antibiotic killing, but the mechanism remains unexplored. In this study, we investigated the effects of intermediate metabolites of the P cycle regarding the potentiation of gentamicin. We found that α-ketoglutarate (α-KG) has the best synergy with gentamicin compared to the other metabolites. This synergistic killing effect was more effective with aminoglycosides than other types of antibiotics, and it was effective against various types of bacterial pathogens. Using fish and mouse infection models, we confirmed that the synergistic killing effect occurred in vivo. Furthermore, functional proteomics showed that α-KG downregulated thiosulphate metabolism. Upregulation of thiosulphate metabolism by exogenous thiosulphate counteracted the killing effect of gentamicin. The role of thiosulphate metabolism in antibiotic resistance was further confirmed using thiosulphate reductase knockout mutants. These mutants were more sensitive to gentamicin killing, and less tolerant to antibiotics compared to their parental strain. Thus, our study highlights a strategy for potentiating antibiotic killing by using a metabolite that reduces antibiotic resistance.

Intestinal epithelial cells of Japanese flounder (Paralichthys olivaceus) as an in vitro model for studying intestine immune function based on transcriptome analysis

Japanese flounder (Paralichthys olivaceus) is an economically crucial marine species, but diseases like hemorrhagic septicemia caused by Edwardsiella tarda have resulted in significant economic losses. E. tarda infects various hosts, and its pathogenicity in fish is not fully understood. Lipopolysaccharides (LPS) are components of the outer membrane of Gram-negative bacteria and are representative of typical PAMP molecules that cause activation of the immune system. The PoIEC cell line is a newly established intestinal epithelial cell line from P. olivaceus. In order to investigate whether it can be used as an in vitro model for studying the pathogenesis of E. tarda and LPS stimulation, we conducted RNA-seq experiments for the PoIECs model of E. tarda infection and LPS stimulation. In this study, transcriptome sequencing was carried out in the PoIEC cell line after treatment with LPS and E. tarda. A total of 62.52G of high-quality data from transcriptome sequencing results were obtained in nine libraries, of which an average of 87.96% data could be aligned to the P. olivaceus genome. Data analysis showed that 283 and 414 differentially expressed genes (DEGs) in the LPS versus Control (LPS-vs-Con) and E. tarda versus Control groups (Et-vs-Con), respectively, of which 60 DEGs were shared in two comparation groups. The GO terms were predominantly enriched in the extracellular space, inflammatory response, and cytokine activity in the LPS-vs-Con group, whereas GO terms were predominantly enriched in nucleus and positive regulation of transcription by RNA polymerase II in the Et-vs-Con group. KEGG analysis revealed that three immune-related pathways were co-enriched in both comparison groups, including the Toll-like receptor signaling pathway, C-type lectin receptor signaling pathway, and Cytokine-cytokine receptor interaction. Five genes were randomly screened to confirm the validity and accuracy of the transcriptome data. These results suggest that PoIEC cell line can be an ideal in vitro model for studies of marine fish gut immunity and pathogenesis of Edwardsiellosis.

Elevated proton motive force is a tetracycline resistance mechanism that leads to the sensitivity to gentamicin in Edwardsiella tarda

Tetracycline is a commonly used human and veterinary antibiotic that is mostly discharged into environment and thereby tetracycline-resistant bacteria are widely isolated. To combat these resistant bacteria, further understanding for tetracycline resistance mechanisms is needed. Here, GC-MS based untargeted metabolomics with biochemistry and molecular biology techniques was used to explore tetracycline resistance mechanisms of Edwardsiella tarda. Tetracycline-resistant E. tarda (LTB4-RTET ) exhibited a globally repressed metabolism against elevated proton motive force (PMF) as the most characteristic feature. The elevated PMF contributed to the resistance, which was supported by the three results: (i) viability was decreased with increasing PMF inhibitor carbonylcyanide-3-chlorophenylhydrazone; (ii) survival is related to PMF regulated by pH; (iii) LTB4-RTET were sensitive to gentamicin, an antibiotic that is dependent upon PMF to kill bacteria. Meanwhile, gentamicin-resistant E. tarda with low PMF are sensitive to tetracycline is also demonstrated. These results together indicate that the combination of tetracycline with gentamycin will effectively kill both gentamycin and tetracycline resistant bacteria. Therefore, the present study reveals a PMF-enhanced tetracycline resistance mechanism in LTB4-RTET and provides an effective approach to combat resistant bacteria.

Aspartate metabolic flux promotes nitric oxide to eliminate both antibiotic-sensitive and -resistant Edwardsiella tarda in zebrafish

Introduction

Metabolic reprogramming potentiates host protection against antibiotic-sensitive or -resistant bacteria. However, it remains unclear whether a single reprogramming metabolite is effective enough to combat both antibiotic-sensitive and -resistant bacteria. This knowledge is key for implementing an antibiotic-free approach.

Methods

The reprogramming metabolome approach was adopted to characterize the metabolic state of zebrafish infected with tetracycline-sensitive and -resistant Edwardsiella tarda and to identify overlapping depressed metabolite in dying zebrafish as a reprogramming metabolite.

Results

Aspartate was identify overlapping depressed metabolite in dying zebrafish as a reprogramming metabolite. Exogenous aspartate protects zebrafish against infection caused by tetracycline-sensitive and -resistant E. tarda. Mechanistically, exogenous aspartate promotes nitric oxide (NO) biosynthesis. NO is a well-documented factor of promoting innate immunity against bacteria, but whether it can play a role in eliminating both tetracycline-sensitive and -resistant E. tarda is unknown. Thus, in this study, aspartate was replaced with sodium nitroprusside to provide NO, which led to similar aspartate-induced protection against tetracycline-sensitive and -resistant E. tarda.

Discussion

These findings support the conclusion that aspartate plays an important protective role through NO against both types of E. tarda. Importantly, we found that tetracycline-sensitive and -resistant E. tarda are sensitive to NO. Therefore, aspartate is an effective reprogramming metabolite that allows implementation of an antibiotic-free approach against bacterial pathogens.

Transcriptome-based nutrigenomics analysis reveals the roles of dietary taurine in the muscle growth of juvenile turbot (Scophthalmus maximus)

The present study explored transcriptomics and gene regulation variations in the muscle of turbot fed with dietary taurine. A 70-day feeding trial was conducted using turbot (initial body weight: 3.66 ± 0.02 g) fed with different levels of dietary taurine: 0 % (C), 0.4 % (T2), 1.2 % (T4) and 2.0 % (T6). Two methods were used to analyze and verify the taurine effects on muscle growth: (1) real-time quantitative PCR (qRT-PCR) for the key muscle growth-related genes and (2) transcriptomic analysis by next-generation sequencing (NGS). The results showed that 1.2 % of dietary taurine supplementation significantly increased the expression of muscle growth stimulatory genes, including TauT, myoD, Myf5, myogenin and follistatin. And also, the 1.2 % level significantly decreased the expression of the muscle growth-restricting gene (myostatin). Meanwhile, transcriptomics analysis found that 1.2 % dietary taurine supplementation significantly increased the number of up-regulated genes linked to metabolic pathways. In contrast, taurine significantly enriched the actin cytoskeleton and metabolic pathways in the T4 and T2 groups, respectively. These findings align with the gene ontology (GO) analysis, which indicated a higher number of cellular component (CC) gene expressions at a 1.2 % of dietary taurine compared to a 0.4 % of dietary taurine supplementation. In conclusion, dietary taurine had positive impacts on the growth-stimulatory genes. Moreover, 1.2 % of dietary taurine supplementation is important to the metabolic pathway enrichment.

Functional proteomics identify mannitol metabolism in serum resistance and therapeutic implications in Vibrio alginolyticus

Serum resistance is recognized as one of the most important pathogenic traits of bacterial pathogens, and no control measure is available. Based on our previous discovery that pathogenic Escherichia coli represses glycine, serine, and threonine metabolism to confer serum resistance and that the reactivation of this pathway by exogenous glycine could restore serum sensitivity, we further investigate the mechanism underlying the action of glycine in Vibrio alginolyticus. Thus, V. alginolyticus is treated with glycine, and the proteomic change is profiled with tandem mass tag-based quantitative proteomics. Compared to the control group, glycine treatment influences the expression of a total of 291 proteins. Among them, a trap-type mannitol/chloroaromatic compound transport system with periplasmic component, encoded by N646_0992, is the most significantly increased protein. In combination with the pathway enrichment analysis showing the altered fructose and mannitol metabolism, mannitol has emerged as a possible metabolite in enhancing the serum killing activity. To demonstrate this, exogenous mannitol reduces bacterial viability. This synergistic effect is further confirmed in a V. alginolyticus-Danio rerio infection model. Furthermore, the mechanism underlying mannitol-enabled serum killing is dependent on glycolysis and the pyruvate cycle that increases the deposition of complement components C3b and C5b-9 on the bacterial surface, whereas inhibiting glycolysis or the pyruvate cycle significantly weakened the synergistic effects and complement deposition. These data together suggest that mannitol is a potent metabolite in reversing the serum resistance of V. alginolyticus and has promising use in aquaculture.