Acute Ammonia Causes Pathogenic Dysbiosis of Shrimp Gut Biofilms

Acute ammonia exposure has detrimental effects on shrimp, but the underlying mechanisms remain to be fully explored. In the present study, we investigated the impact of acute ammonia exposure on the gut microbiota of the white shrimp Litopenaeus vannamei and its association with shrimp mortality. Exposure to a lethal concentration of ammonia for 48 h resulted in increased mortality in L. vannamei, with severe damage to the hepatopancreas. Ammonia exposure led to a significant decrease in gut microbial diversity, along with the loss of beneficial bacterial taxa and the proliferation of pathogenic Vibrio strains. A phenotypic analysis revealed a transition from the dominance of aerobic to facultative anaerobic strains due to ammonia exposure. A functional analysis revealed that ammonia exposure led to an enrichment of genes related to biofilm formation, host colonization, and virulence pathogenicity. A species-level analysis and experiments suggest the key role of a Vibrio harveyi strain in causing shrimp disease and specificity under distinct environments. These findings provide new information on the mechanism of shrimp disease under environmental changes.

Adverse effects of chronic ammonia stress on juvenile oriental river prawn (Macrobrachium nipponense) and alteration of glucose and ammonia metabolism

Ammonia is one of the common stress factors in aquaculture. However, the effect of chronic ammonia exposure in juvenile oriental river prawn (Macrobrachium nipponense) is currently unexplored. This study explored the effects of chronic ammonia on juvenile healthy oriental river prawns. Fifty prawns (0.123 ± 0.003 g) were exposed to 0, 5, and 15 mg/L total ammonia nitrogen (TAN) in triplicates for 28 days. The effects of chronic ammonia challenge were evaluated on growth, antioxidant capacity, hepatopancreas and gill morphology, and glucose and ammonia metabolism. The results showed that, the chronic ammonia exposure reduced significantly survival rate and weight gain of prawns. The prawns exposed to 15 mg/L ammonia had induced oxidative stress. However, the prawn exposed to 15 mg/L ammonia had significantly lower aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, and acid phosphatase activities in the serum. Furthermore, exposure of prawns to 15 mg/L ammonia increased the activities of hexokinase, pyruvate kinase, pyruvate and lactic acid content, and glutamine synthase activity. However, the prawns exposed to 15 mg/L ammonia, reduced succinic dehydrogenase, 6-phosphogluconic dehydrogenase, phosphoenolpyruvate carboxykinase, glutamate synthase, and glutamate dehydrogenase activities but increased ammonia content in serum. The exposure of ammonia deformed lumen, damaged basement membrane and decreased secretory cells in the hepatopancreas, disordered gill epithelial and pillar cells, and caused gill filament base vacuolation. Our study indicates that chronic ammonia stress impairs growth performance, tissue morphology, induces oxidative stress, and alters glucose and ammonia metabolism in juvenile oriental river prawns.

Liver Injury and Metabolic Dysregulation in Largemouth Bass (Micropterus salmoides) after Ammonia Exposure

Elevated environmental ammonia leads to respiratory disorders and metabolic dysfunction in most fish species, and the majority of research has concentrated on fish behavior and gill function. Prior studies have rarely shown the molecular mechanism of the largemouth bass hepatic response to ammonia loading. In this experiment, 120 largemouth bass were exposed to total ammonia nitrogen of 0 mg/L or 13 mg/L for 3 and 7 days, respectively. Histological study indicated that ammonia exposure severely damaged fish liver structure, accompanied by increased serum alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase activity. RT-qPCR results showed that ammonia exposure down-regulated the expression of genes involved in glycogen metabolism, tricarboxylic acid cycle, lipid metabolism, and urea cycle pathways, whereas it up-regulated the expression of genes involved in gluconeogenesis and glutamine synthesis pathways. Thus, ammonia was mainly converted to glutamine in the largemouth bass liver during ammonia stress, which was rarely further used for urea synthesis. Additionally, transcriptome results showed that ammonia exposure also led to the up-regulation of the oxidative phosphorylation pathway and down-regulation of the mitogen-activated protein kinase signaling pathway in the liver of largemouth bass. It is possible that the energy supply of oxidative phosphorylation in the largemouth bass liver was increased during ammonia exposure, which was mediated by the MAPK signaling pathway.

The alterations of tracheal microbiota and inflammation caused by different levels of ammonia exposure in broiler chickens

Ammonia (NH3) is a known harmful gas and exists in haze, forming secondary organic aerosols. Exposure to ambient ammonia correlates with the respiratory tract infection, and microbiota in the upper respiratory tract is an emerging crucial player in the homeostatic regulation of respiratory tract infection, and microbiota perturbation is usually accompanied by the inflammatory reactions; however, the effects of different levels of ammonia exposure on tracheal microbiota and inflammation are unclear. A total of 288 22-day-old male Arbor Acres broilers were chosen and divided into 4 groups with 6 replicates of 12 chickens, and respectively exposed to ammonia at 0, 15, 25, and 35 ppm for 21-d trial period. Cytokines (interleukin (IL)-1β, IL-6, and IL-10) in the trachea were measured at the 21 d of exposure to NH3. Tracheal microbiota at the 21 d was analyzed by the 16S rRNA gene analysis. The results showed that an increase in ammonia levels, even in 15 ppm, significantly decreased the alpha diversity and changed the bacterial community structure. Six genera (Faecalibacterium, Ruminococcus]_torques_group, unclassified_f__Lachnospiraceae, Ruminococcaceae_UCG-014, Streptococcus, Blautia) significantly increased, whereas Lactobacillus significantly decreased under different levels of ammonia exposure. We also observed positive associations of Faecalibacterium, Blautia, g__Ruminococcaceae_UCG-014, unclassified_f__Lachnospiraceae and Ruminococcus]_torques_group abundances with tracheal IL-1β concentration. Moreover, an increase in ammonia levels, even in 15 ppm, caused respiratory tract inflammatory injury. The results indicated that 15 ppm ammonia exposure changed the composition of tracheal microbiota that caused the tracheal injury possibly through increasing the IL-1β, which might make the broiler more sensitive to the changes of environment and pathogenic micro-organisms in the poultry house, and may be also a critical value that needs high alertness. Herein, the present experiment also suggested that the standard limit of ammonia concentration in adult poultry house is 15 ppm. This research provides an insight into the relationship between the upper respiratory tract microbiota and inflammation under ammonia exposure.