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The intestine barrier serves as the front-line defense in shrimp. Clostridium butyricum (CB) can produce butyric acid that provides energy for the intestine epithelial cells of the host. However, the effects of dietary CB on the intestine microbiome and the digestion and immunity of the host is not clear. In this study, we therefore investigated the composition and metabolic activity of the intestine microbiome, and digestive and immune-related gene expression in Litopenaeus vannamei fed with diets containing different levels of CB: basal diet (control), 2.5 × 109 CFU kg−1 diet (CB1), 5.0 × 109 CFU kg−1 diet (CB2), and 1.0 × 1010 CFU kg−1 diet (CB3) for 56 days. Dietary CB altered the composition of the intestine microbiome. Specifically, the dominant bacterial phylum Proteobacteria was enriched in the CB3 group and weakened in the CB1 and CB2 groups. The Bacteroidetes was enriched in the CB1 and CB2 groups and weakened in the CB3 group. The Firmicutes was enriched in all three CB groups. At the genus level, the potential pathogen (Desulfovibrio and Desulfobulbus) were weakened, and beneficial bacteria (Bacillus, Clostridium, Lachmoclostridium, Lachnospiraceae, and Lactobacillus) were enriched in response to dietary CB; these might contribute to the expression of the host digestive genes (α-amylase, lipase, trypsin, fatty acid-binding protein, and fatty acid synthase) and immune-related genes (prophenoloxidase, lipopolysaccharide and β-1,3-glucan binding protein, lysozyme, crustin, and superoxide dismutase). Additionally, CB enhanced the bacterial metabolism, especially that of carbohydrates, polymers, amino acids, carboxylic acids, and amines. These results revealed that dietary CB had a beneficial effect on the intestine health of L. vannamei by modulating the composition of the intestine microbiome, enhancing the microbial metabolism activity, and promoting the digestion and immunity of the host. The optimal dietary supplementation dosage was found to be 5.0 × 109 CFU kg−1 in the diet.

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Technologically controlling nanostructures is essential to tailoring the functionalities and properties of nanomaterials. Various methods free from lithography-based techniques have been employed to fabricate 2D nanostructures; however it is still hard to achieve a well interconnected 2D regular nanostructure. Here, we demonstrate a facile chemical solution method to self-assemble a regular and interconnected VO2 nanonet on the wafer scale. The nanonet shows a well-defined 2D truss network constructed by VO2 nanorods with twinning relationships. The growth direction and crystallographic orientation of nanorods are synchronously controlled, leading to horizontally epitaxial growth of nanorods along three symmetric directions of the (001) single-crystal sapphire substrate. The unique nanonets enable the acquisition of excellent resistance switching properties and dramatic fatigue endurance. A large resistance change of near 5 orders with a 1.7 °C width of the hysteresis loop is characterized comparably to the properties of single crystals without detectable degradation after 500 cycles over the metal-to-insulator transition. It indicates that the nanonet can serve as an exceptional candidate for practical application in switching functional devices. Our findings offer a novel pathway for self-assembly of 2D ordered nanostructures, which would provide new opportunities for the bottom-up integration of nanodevices.

Structural stability and functional performances of vanadium dioxide (VO) are strongly influenced by oxygen vacancies. However, the mechanism of metal-insulator transition (MIT) influenced by defects is still under debate. Here, we study the evolution of structure and electrical property of oxygen-deficient VO by a low temperature annealing process (LTP) based on a truss-structured VO nanonet. The oxygenation process of the oxygen-deficient VO is greatly prolonged, which enables us to probe the gradual change of properties of the oxygen-deficient VO. A continuous lattice reduction is observed during LTP. No recrystallization and structural collapse of the VO nanonet can be found after LTP. The valence-band X-ray photoelectron spectroscopy (XPS) measurements indicate that the oxygen deficiency strongly affects the energy level of the valence band edge. Correspondingly, the resistance changes of the VO films from 1 to 4.5 orders of magnitude are achieved by LTP. The effect of oxygen vacancy on the electric field driven MIT is investigated. The threshold value of voltage triggering the MIT decreases with increasing the oxygen vacancy concentration. This work demonstrates a novel and effective way to control the content of oxygen vacancies in VO and the obvious impact of oxygen vacancy on MIT, facilitating further research on the role of oxygen vacancy in structure and MIT of VO, which is important for the deep understanding of MIT and exploiting innovative functional application of VO.

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