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Skin ulceration syndrome (SUS) as a main disease in Apostichopus japonicus aquaculture has severely restricted the developmental A. japonicus aquaculture industry. Intestinal microbiota (IM) has been studied extensively due to its immunomodulatory properties. Short-chain fatty acids (SCFAs) as an essential signal molecule for microbial regulation of host health also have attracted wide attention. Therefore, it is beneficial to explore the link between IM and SUS for prevention and control of SUS. In the study, the contribution of IM to SUS development has been examined. Additionally, our research further validated the restoration of SCFAs on intestinal barrier dysfunction caused by SUS via isolating SCFAs-producing bacteria. Notably, this restoration might be achieved by inhibition of NF-κB–MLCK–MLC signal pathway, which could be activated by V. splendidus . These findings may have important implications for exploration of the role of IM in SUS occurrence and provide insight into the SUS treatment.

Iron is essential for bacterial survival and pathogenicity. During infection, bacteria face iron limitation imposed by the host and must develop strategies to obtain iron and maintain virulence. The ferric uptake regulator (Fur) is a major iron-responsive regulator that coordinates iron metabolism and virulence-related functions in many bacteria. However, whether and how Fur regulates virulence systems in the Apostichopus japonicus pathogen Vibrio splendidus remains unclear. In this study, the VsFur-knockdown strain was used to investigate the role of VsFur in T6SS regulation and virulence-associated traits. Aggregation and adhesion assays showed that knockdown of VsFur reduced bacterial aggregation and adhesion to coelomocytes of the A. japonicus. qPCR and Western blot analyses revealed that iron limitation and VsFur knockdown both significantly inhibited the expression of T6SS-related genes and the secretion of Hcp. In terms of mechanism, VsFur directly bound to the promoter region of the T6SS gene cluster and positively regulated its transcription. ELISA and immunofluorescence analyses further showed that knockdown of VsFur significantly reduced the secretion and host–cell delivery of the T6SS effector proteins Hcp and VgrG. Moreover, hemolysis and siderophore production assays showed that VsFur knockdown enhanced hemolytic activity and siderophore production, suggesting the existence of a compensatory mechanism. Collectively, these results reveal a novel regulatory relationship between VsFur and virulence in V. splendidus, providing new insights into iron-dependent virulence regulation and a theoretical basis for the development of novel strategies for the prevention of bacterial diseases in A. japonicus aquaculture.

The conduction heating device for full-scale automobile safety parts was investigated and developed in the present study. The heating and forming tests of the blanks of ultra-high-strength steel were conducted on the device. The influence of unequal radiation heat transfer strategy on the steady temperature distributions of the blanks was studied. The forming accuracy, mechanical properties, and microstructure of the front bumper parts via conduction heating were also investigated. The results showed that the material utilization rate of the blanks increased by 31.1% in the unequal radiation heat transfer condition. The forming accuracy of the front bumper parts fluctuated within the range of + 0.595 mm and − 0.845 mm. The Vickers hardness of the uniform temperature regions was more than 480 HV. The balance of strength and ductility of the uniform temperature regions was more than 11.1 GPa%. The full martensite microstructure was obtained in the front bumper parts.

The uptake and utilization of iron by bacteria must be strictly controlled. The ferric uptake regulator (Fur) is a global transcription factor widely present in bacteria that can perceive cellular iron levels and adjust the expressions of various genes accordingly. Our earlier research demonstrated that the knockdown of the fur gene in Vibrio splendidus significantly reduced its lethality to Apostichopus japonicus. Although the functions and mechanisms of Fur in regulating bacterial virulence genes have been extensively studied, its virulence regulatory network during V. splendidus pathogenesis in A. japonicus remains unclear. In this article, transcriptome sequencing analysis of V. splendidus under different iron conditions reveals substantial differential gene expressions in the simulated pathogenic environments, identifying 1185 differentially expressed genes, including 198 downregulated and 987 upregulated genes. Comparative analysis between wild-type and Vsfur knockdown strains shows that Vsfur knockdown altered the expression of 3593 genes in V. splendidus, with the most significant differential expression observed under simulated pathogenic conditions (1030 upregulated and 72 downregulated). KEGG enrichment analysis indicates that Vsfur knockdown caused significant gene enrichment in the flagellar assembly pathway and bacterial secretion system, critically impairing flagellar synthesis and secretion system function in V. splendidus. Eight genes selected for qRT-PCR validation showed expression levels in line with the RNA-seq results. Consistent with the transcriptomic results, Vsfur knockdown resulted in reduced antioxidant capacity, bacterial competitiveness, and cytotoxicity in V. splendidus. These findings elucidate the virulence regulatory mechanism of Fur in V. splendidus and provide a reference for understanding the occurrence of A. japonicus skin ulcer syndrome.

Vibrio splendidus is an opportunistic pathogen that causes skin ulcer syndrome and results in huge losses to the Apostichopus japonicus breeding industry. Ferric uptake regulator (Fur) is a global transcription factor that affects varieties of virulence-related functions in pathogenic bacteria. However, the role of the V. splendidus fur ( Vsfur ) gene in the pathogenesis of V. splendidus remains unclear. Hence, we constructed a Vsfur knock-down mutant of the V. splendidus strain (MTVs) to investigate the role of the gene in the effect of biofilm, swarming motility, and virulence on A. japonicus . The result showed that the growth curves of the wild-type V. splendidus strain (WTVs) and MTVs were almost consistent. Compared with WTVs, the significant increases in the transcription of the virulence-related gene Vshppd mRNA were 3.54- and 7.33-fold in MTVs at the OD 600 of 1.0 and 1.5, respectively. Similarly, compared with WTVs, the significant increases in the transcription of Vsm mRNA were 2.10- and 15.92-fold in MTVs at the OD 600 of 1.0 and 1.5, respectively. On the contrary, the mRNA level of the flagellum assembly gene Vsflic was downregulated 0.56-fold in MTVs at the OD 600 of 1.0 compared with the WTVs. MTVs caused delayed disease onset time and reduced A. japonicus mortality. The median lethal doses of WTVs and MTVs were 9.116 × 10 6 and 1.658 × 10 11  CFU·ml −1 , respectively. Compared with WTVs, the colonization abilities of MTVs to the muscle, intestine, tentacle, and coelomic fluid of A. japonicus were significantly reduced. Correspondingly, the swarming motility and biofilm formation in normal and iron-replete conditions were remarkably decreased compared with those of WTVs. Overall, these results demonstrate that Vsfur contributes to the pathogenesis of V. splendidus by regulating virulence-related gene expression and affecting its swarming and biofilm formation abilities.

In this study, austenitizing heat treatment before hot stamping of Al-10% Si coated boron steel is first investigated through environment scanning electron microscopy (ESEM) equipped with energy dispersive x-ray analysis (EDAX). The cracking behavior of the coating was evaluated using Gleeble 3500, a thermo-mechanical simulator under uniaxial plastic deformation at elevated temperatures. The extent and number of cracks developed in the coating were carefully assessed through an optical microscope. The coating layer under hot-dipped condition consists of an Al-Si eutectic matrix, Fe2Al7Si, Fe3Al2Si3 and Fe2Al5, from the coating surface to the steel substrate. The coating layer remains dense, continuous and smooth. During austenitization, the Al-rich Fe-Al intermetallics in the coating transform to more Fe-rich intermetallics, promoted by the Fe diffusion process. The coating finally shows the coexistence of two types of Fe-Al intermetallics, namely, FeAl2 and FeAl. Microcracks and Kirkendall voids occur in the coating layer and diffusion zone, respectively. The coating is heavily cracked and broken into segments during the hot tensile tests. Bare steel exposed between the separate segments of the coating is oxidized and covered with a thin FeOx layer. The appearance of the oxide decreases the adhesion of the Al-Si coating. It is found that the ductile FeAl is preferred as a coating microstructure instead of the brittle FeAl2. Therefore, the ductility of the Al-Si coating on hot stamping boron steel could be enhanced by controlling the ductile Fe-rich intermetallic phase transformations within it during austenitization. Experiments indicate that a higher austenitizing temperature or longer dwell time facilitate the Fe-rich intermetallics transformation, increasing the volume fraction of FeAl. This phase transformation also contributes to reducing the crack density and depth.

The Al-Si coating of ultra-high strength steel has been applied to hot stamping more and more widely, owing to solving the problem of oxidation and decarburization. However, the evolution of Al-Si coating during the heating process was rarely studied in the previous study. The tests about the influence of heating parameters, such as heating temperature, heating rates and dwell time, on properties of the Al-Si coating were carried out on the Gleeble-3500 thermal simulator. The properties of the Al-Si coating, for instance, volume fraction of FeAl intermetallics, α-Fe layer as well as porosity and 3D surface topography, were explored in the study. Results showed that more and more Kirkendall voids and cracks appeared in the Al-Si coating when the heating temperature exceeded 600°C. The heating rates almost had no influence on properties of the Al-Si coating when the temperature was equal to or lower than 500°C. The volume fraction of FeAl intermetallics in the coating with dwell time from 3 s to 8 min at 930°C was 0, 6.19%, 17.03% and 20.65%, separately. The volume fraction of the α-Fe layer in the coating changed from zero to 31.52% with the prolonged dwell time. The porosity of the coating ranged from 0.51% to 4.98% with the extension of dwell time. The unsmooth degree of the surface of the coating rose gradually with the increasing of heating rates and the extension of dwell time. The 3D surface topography of the coating was determined by the comprehensive effect of atoms diffusion, new formed phases, surface tension and the degree of oxidation of the coating surface. Experiments indicated that rapid heating was not suitable for the coating when the temperature exceeded 500°C. Experiments also demonstrated that enough dwell time was essential to obtain the superior properties of the coating.

To improve mechanical and thermal properties of jute fibers (JFs) reinforced polypropylene (PP) composites, a surface treatment method by grafting graphene oxide nanoplatelets (GONPs) onto JFs was developed. The GONPs effectively enhanced the interfacial adhesion between JFs and PP matrix via improving mechanical interlocking. The results show that PP/JFs-KH570-GONPs composites had the significant improvement of 16.2 % and 12.4 % in tensile and flexural strength, respectively. And the thermal property of PP/JFs-Silane-GONPs composites was also improved after treatment. These high performance composites have the potential to be applied in many fields, such as the automotive industry, household products and so on.

In this study, a thermo-plastic-martensite transformation coupled model based on the von Mises yield criterion and the associated plastic flow rule is developed to further improve the accuracy of numerical simulation during hot stamping. The constitutive model is implemented into the finite element program ABAQUS using user subroutine VUMAT. The martensite transformation, transformation-induced plasticity and volume expansion during the austenite-to-martensite transformation are included in the constitutive model. For this purpose, isothermal tensile tests are performed to obtain the flow stress, and non-isothermal tensile tests were carried out to validate the constitutive model. The non-isothermal tensile numerical simulation demonstrates that the thermo-plastic-martensite transformation coupled constitutive model provides a reasonable prediction of force-displacement curves upon loading, which is expected to be applied for modeling and simulation of hot stamping.

In traditional hot stamping process, heating of the sheet by radiation heating occupies most of cycle time, which limits the application of hot stamping in automotive industry. Thus a faster heating method has great significance on the hot stamping. The conduction heating overcomes shortage of the radiation heating because of higher heating rate and greater energy efficiency. It attracts increasing attention in the application of heating blanks in hot stamping. In the present study, a movable conduction heating device on die was designed in terms of the Joule’s Law. Heating experiments of boron alloyed steel were performed using the developed device. Heating rate and uniform temperature region were investigated in the non-heat preservation condition (NHPC) and the heat preservation condition (HPC). The results revealed that in the HPC, the heating rate was improved by 13.1 °C/s. In addition, the length of the uniform temperature region was lengthened by 15 mm. It was demonstrated that the HPC was preferred. Furthermore, it was indicated that the mechanical properties of the blanks in uniform temperature region of the conduction heating were also superior to that of the radiation heating.