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The aim of this study was to investigate the dynamic changes in the microbial communities of both the environment and gut of Litopenaeus vannamei, as well as to elucidate the mechanisms underlying microbial community assembly in greenhouse farming. 16S rDNA high-throughput sequencing and bioinformatics methods were used to carry out the research on the community structure of the microorganisms under greenhouse culture conditions in water, sediment, and gut microorganisms; correlations pertaining to environmental factors; the feasibility of using Source Tracker; and the mechanisms of community construction. The results show that the dominant microorganisms in water, sediment, and gut farming in a greenhouse environment varied and were subject to dynamic change. A variety of beneficial microbiota such as Bacillus were found in the gut, whereas a variety of microorganisms such as Marivita and Pseudomonas, which function as nitrogen and phosphorus removers, were present in water. Source Tracker and environmental correlation analyses showed that changes in the gut were associated with eutrophication indicators (total nitrogen, total phosphorus, ammonia nitrogen) and changes in environmental microorganisms (in water and sediment). The results of the community-building mechanism analysis show that stochastic processes determine the community-building directions of environmental and gut microorganisms. These findings will help us to understand the microbiota characteristics of shrimp ponds under greenhouse farming conditions, and the complex interactions between the shrimp gut and the environmental microbiota and environmental variables, as well as revealing the changing rules of the gut microbiota. [ABSTRACT FROM AUTHOR]

Temperature is a limiting factor in the growth of aquatic organisms and can directly affect many chemical and biological processes, including metabolic enzyme activity, aerobic respiration, and signal transduction. In this study, physiological, transcriptomic, and metabolomic analyses were performed to characterize the response of Litopenaeus vannamei to cold stress. We subjected L. vannamei to gradually decreasing temperatures (24 °C, 20 °C, 18 °C, 14 °C, and 12 °C) and studied the changes in the hepatopancreas. The results showed that extreme cold stress (12 °C) caused structural damage to the hepatopancreas of L. vannamei. However, shrimp exhibited response mechanisms to enhance cold tolerance, through regulating changes in key genes and metabolites in amino acid, lipid metabolism, and carbohydrate metabolism, including (a) increased level of methylation in cells to enhance cold tolerance; (b) increased content of critical amino acids, such as proline, alanine, glutamic acid and taurine, to ameliorate energy metabolism, protect cells from cold-induced osmotic imbalance, and promote ion transport and DNA repair; (c) accumulation of unsaturated fatty acids to improve cell membrane fluidity; and (d) regulation of the metabolic pattern shift to rely on anaerobic metabolism with a gradual decrease in aerobic metabolism and enhance glycolysis to produce enough ATP to maintain energy metabolic balance. When the temperature dropped further, cold stress impaired antioxidant and immune defense responses in shrimp. This study provides an integrated analysis of the physiology, transcriptome, and metabolome of L. vannamei in response to cold stress. [Display omitted] • Cold stress caused damage to the hepatopancreas structure of L. vannamei. • Increased amino acids to ameliorate energy metabolism and enhance osmotic balance • Transcriptome and metabolome results support methylation, energy and unsaturated fatty acid production. • Cold stress resulted in impaired antioxidant and immune defense responses in shrimp. • Shrimp can enhance tolerance to cold stress via integrated adjustments. [ABSTRACT FROM AUTHOR]

• Bacterial diversity in the intestine of L. vannamei decreased with increasing severity of EHP infection. • The relative abundance of Planctomycetes, Actinobacteria and Acidobacteria phyla decreased significantly with severity of EHP infection (P < 0.05). • The relative abundance of Pseudomonas , Bradyrhizobium, Bacteroides and Vibirio increased significantly with severity of EHP infection (P < 0.05) The intestinal microbiota of the Pacific white shrimp Litopenaeus vannamei during Enterocytozoon hepatopenaei (EHP) infection was investigated by 16S rRNA gene-based analysis. The results showed that bacterial diversity in the intestine of L. vannamei was high, but it decreased with increasing severity of EHP infection. The relative abundances of the phyla Planctomycetes, Actinobacteria and Acidobacteria decreased significantly with a decrease in body size or EHP infection severity (P < 0.05). The most abundant genera were Pseudomonas , Methylobacterium, Bradyrhizobium, Bacteroides, Vibrio, Prevotella and so on. In addition, the relative abundances of some bacteria, such as Pseudomonas, Bradyrhizobium, Bacteroides and Vibrio, increased significantly with a decrease in body size or EHP infection severity (P < 0.05). These findings suggest that changes in the intestinal microbiota occur depending on the severity of EHP infection. [ABSTRACT FROM AUTHOR]