New insights into the influence of myo-inositol on carbohydrate metabolism during osmoregulation in Nile tilapia (Oreochromis niloticus)

Transcriptome Analysis Reveals the Key Genes and Pathways for Growth, Ion Transport, and Oxidative Stress in Post-Larval Black Tiger Shrimp (Penaeus monodon) Under Acute Low Salt Stress

As an abiotic stress factor, salinity significantly affects the physiological activities of crustaceans. In this study, transcriptome sequencing was used to evaluate the mechanism of ion transport and the physiological response of black tiger shrimp (Penaeus monodon) under low salt stress. Four hundred post larval (PL) stage P. monodon were distributed in eight experimental tanks and exposed to 3 or 5 ppt salt concentrations for 96 h. Low salinity significantly reduced the survival rate of shrimp but simultaneously activated the activity of ion transporter enzymes Na+/K+-ATPase (NKA) and Ca2+/Mg2+-ATPase), the expression of NKA, galectin 10, and cytochrompe c peroxidase genes, and the activity and expression of antioxidant-related genes (superoxide dismutase, catalase, heat shock protein 60). Low salt stress activated the urea cycle but significantly inhibited glutathione metabolization-related indicators (glutamate dehydrogenase, glutaminase, glutamic acid). RNA-seq analysis identified 221 differentially expressed genes (78 up-regulated and 143 down-regulated). Quantitative real-time PCR and RNA-seq results of 11 of them were consistent, illustrating the validity of the transcriptomic predictions. Gene set enrichment analysis results showed that calcium ion transmembrane transport, calmodulin binding, the stress-activated protein kinase signaling cascade, and regulation of the cytosolic calcium ion concentration process were significantly enriched. These results showed that low salt stress activated the calcium-dominated ion transport pathway and promoted molting growth of P. monodon. They also indicate that there is potential for larval rearing shrimp under low salt conditions.

Effects of Diets With Different Carbohydrate to Lipid Ratios on the Growth Performance, Ion Transport, and Carbohydrate, Lipid and Ammonia Metabolism of Nile Tilapia (Oreochromis niloticus) Under Long-Term Saline-Alkali Stress

A 50-day test was adopted to compare the growth performance, liver histology, glucose metabolism, lipid (L) metabolism, ion transport, and ammonia metabolism of tilapia fed different carbohydrate-lipid (C:L) ratio diets under saline-alkaline water (salinity = 16 mmol/L and alkalinity = 35 mmol/L). The C and L levels of five isoenergetic (16.5 kJ/g) and isonitrogenous (32% protein) diets were C45%:L3% (L3), C38%:L6% (L6), C31%:L9% (L9), C24%:L12% (L12), and C17%:L15% (L15). This study found that the dietary C:L ratio did not affect the survival rate (SR), feed conversion ratio (FCR), or condition factor of tilapia in saline-alkali water, but fish in the L12 group had the highest weight gain (WG) rate and the lowest hepatosomatic index (HSI) compared with the other groups. Fish fed the higher C diet (L3 and L6) had a higher ion transport capacity and ammonia excretion capacity in gills. However, the highest mRNA expression of genes involved in glutamine metabolism and urea metabolism in the liver was found in the high-L diet groups (L12 and L15). In particular, a lower serum ammonia concentration was observed in the high-L diet groups (L12 and L15). In addition, biochemical indicators indicated that the L12 group had the highest liver pyruvic acid, lactic dehydrogenase (LDH), and lipase (LPS) and serum total cholesterol (T-CHO) contents. In summary, this study indicated that dietary Ls could promote glutamine metabolism and urea metabolism more than dietary Cs and then reduce the serum ammonia concentration of tilapia in saline-alkali water. A dietary C:L ratio of 2:1 was beneficial to the growth and ammonia excretion of tilapia in saline-alkali water in this study.

The Effect of High Levels Carbohydrate on Intestinal Microbiota, Metabolites, and Health of Common Carp (Cyprinus carpio L.)

Long-term consumption of high-carbohydrate feed may adversely affect intestinal health of fish; however, the underlying roles remain ambiguous. This study examined the effects of varying carbohydrate levels on the intestinal flora of common carp and assessed how microbial metabolites influence intestinal health. Two hundred seventy common carps were chosen and distributed randomly into three groups that fed diets containing starch at levels of 15% (low-carbohydrate diet [LCD]), 28% (medium-carbohydrate diet [MCD]), and 45% (high-carbohydrate diet [HCD]) for 60 days. A significant increase in final body weight, weight gain rate, and specific growth rate within the MCD group, while feed conversion ratio exhibited a decrease in comparison to the other groups (p < 0.05). Feeding with a HCD led to decreased activity of catalase and increased malondialdehyde content, which was consistent with reverse transcription-quantitative real-time polymerase chain reaction (RT-qPCR) analysis results (p < 0.05). Specifically, the RT-qPCR results revealed that HCD treatment significantly upregulated il1β, il6, and il8 transcript levels. Whereas, the il10 messenger RNA (mRNA) was markedly reduced in comparison to the LCD group. Furthermore, the HCD group exhibited an increased abundance of Proteobacteria, accompanied by a reduction in Fusobacteria abundance, and also revealed an upsurge in opportunistic pathogenic bacteria, such as Aeromonas and Shewanella. The correlation analysis demonstrated negative correlations of anti-inflammatory active substances such as fucoxanthin, (S)-reticuline, hecogenin, and uridine with Aeromonas, but positive correlations with Luteolibacter. In summary, dietary carbohydrates might mediate intestinal flora to regulate their metabolites and affect intestinal inflammatory response.

Proline metabolism is essential for alkaline adaptation of Nile tilapia (Oreochromis niloticus)

BACKGROUND

Saline-alkaline water aquaculture has become a key way to mitigate the reduction of freshwater aquaculture space and meet the increasing global demand for aquatic products. To enhance the comprehensive utilization capability of saline-alkaline water, it is necessary to understand the regulatory mechanisms of aquatic animals coping with saline-alkaline water. In this study, our objective was to elucidate the function of proline metabolism in the alkaline adaptation of Nile tilapia (Oreochromis niloticus).

RESULTS

Expose Nile tilapia to alkaline water of different alkalinity for 2 weeks to observe changes in its growth performance and proline metabolism. Meanwhile, to further clarify the role of proline metabolism, RNA interference experiments were conducted to disrupt the normal operation of proline metabolic axis by knocking down pycr (pyrroline-5-carboxylate reductases), the final rate-limiting enzyme in proline synthesis. The results showed that both the synthesis and degradation of proline were enhanced under carbonate alkalinity stress, and the environmental alkalinity impaired the growth performance of tilapia, and the higher the alkalinity, the greater the impairment. Moreover, environmental alkalinity caused oxidative stress in tilapia, enhanced ion transport, ammonia metabolism, and altered the intensity and form of energy metabolism in tilapia. When the expression level of the pycr gene decreased, the proline metabolism could not operate normally, and the ion transport, antioxidant defense system, and energy metabolism were severely damaged, ultimately leading to liver damage and a decreased survival rate of tilapia under alkalinity stress.

CONCLUSIONS

The results indicated that proline metabolism plays an important role in the alkaline adaptation of Nile tilapia and is a key regulatory process in various biochemical and physiological processes.

Effects of CRISPR/Cas9 targeting of the myo-inositol biosynthesis pathway on hyper-osmotic tolerance of tilapia cells

Myo-inositol is an important compatible osmolyte in vertebrates. This osmolyte is produced by the myo-inositol biosynthesis (MIB) pathway composed of myo-inositol phosphate synthase and inositol monophosphatase. These enzymes are among the highest upregulated proteins in tissues and cell cultures from teleost fish exposed to hyperosmotic conditions indicating high importance of this pathway for tolerating this type of stress. CRISPR/Cas9 gene editing of tilapia cells produced knockout lines of MIB enzymes and control genes. Metabolic activity decreased significantly for MIB KO lines in hyperosmotic media. Trends of faster growth of the MIB knockout lines in isosmotic media and faster decline of MIB knockout lines in hyperosmotic media were also observed. These results indicate a decline in metabolic fitness but only moderate effects on cell survival when tilapia cells with disrupted MIB genes are exposed to hyperosmolality. Therefore MIB genes are required for full osmotolerance of tilapia cells.

Study on the osmotic response and function of myo-inositol oxygenase in euryhaline fish nile tilapia (Oreochromis niloticus)

To understand the role of myo-inositol oxygenase (miox) in the osmotic regulation of Nile tilapia, its expression was analyzed in various tissues. The results showed that the expression of miox gene was highest in the kidney, followed by the liver, and was significantly upregulated in the kidney and liver under 1 h hyperosmotic stress. The relative luminescence efficiency of the miox gene transcription starting site (-4,617 to +312 bp) under hyperosmotic stress was measured. Two fragments (-1,640/-1,619 and -620/-599) could induce the luminescence activity. Moreover, the -1,640/-1,619 and -620/-599 responded to hyperosmotic stress and high-glucose stimulation by base mutation, suggesting that osmotic and carbohydrate response elements may exist in this region. Finally, the salinity tolerance of Nile tilapia was significantly reduced after the knocking down of miox gene. The accumulation of myo-inositol was affected, and the expression of enzymes in glucose metabolism was significantly reduced after the miox gene was knocked down. Furthermore, hyperosmotic stress can cause oxidative stress, and MIOX may help maintain the cell redox balance under hyperosmotic stress. In summary, MIOX is essential in osmotic regulation to enhance the salinity tolerance of Nile tilapia by affecting myo-inositol accumulation, glucose metabolism, and antioxidant performance.NEW & NOTEWORTHY Myo-inositol oxygenase (MIOX) is the rate-limiting enzyme that catalyzes the first step of MI metabolism and determines MI content in aquatic animals. To understand the role of miox in the osmotic regulation of Nile tilapia, we analyzed its expression in different tissues and its function under hyperosmotic stress. This study showed that miox is essential in osmotic regulation to enhance the salinity tolerance of Nile tilapia by affecting myo-inositol accumulation, glucose metabolism, and antioxidant performance.

Genome-wide identification, characterization, and expression analysis of MIPS family genes in legume species

BACKGROUND

Evolutionarily conserved in plants, the enzyme D-myo-inositol-3-phosphate synthase (MIPS; EC 5.5.1.4) regulates the initial, rate-limiting reaction in the phytic acid biosynthetic pathway. They are reported to be transcriptional regulators involved in various physiological functions in the plants, growth, and biotic/abiotic stress responses. Even though the genomes of most legumes are fully sequenced and available, an all-inclusive study of the MIPS family members in legumes is still ongoing.

RESULTS

We found 24 MIPS genes in ten legumes: Arachis hypogea, Cicer arietinum, Cajanus cajan, Glycine max, Lablab purpureus, Medicago truncatula, Pisum sativum, Phaseolus vulgaris, Trifolium pratense and Vigna unguiculata. The total number of MIPS genes found in each species ranged from two to three. The MIPS genes were classified into five clades based on their evolutionary relationships with Arabidopsis genes. The structural patterns of intron/exon and the protein motifs that were conserved in each gene were highly group-specific. In legumes, MIPS genes were inconsistently distributed across their genomes. A comparison of genomes and gene sequences showed that this family was subjected to purifying selection and the gene expansion in MIPS family in legumes was mainly caused by segmental duplication. Through quantitative PCR, expression patterns of MIPS in response to various abiotic stresses, in the vegetative tissues of various legumes were studied. Expression pattern shows that MIPS genes control the development and differentiation of various organs, and have significant responses to salinity and drought stress.

CONCLUSION

The MIPS genes in the genomes of legumes have been identified, characterized and their expression was analysed. The findings pave way for understanding their molecular functions and evolution, and lead to identify the putative MIPS genes associated with different cell and tissue development.

Reducing Dietary Protein Content by Increasing Carbohydrates Is More Beneficial to the Growth, Antioxidative Capacity, Ion Transport, and Ammonia Excretion of Nile Tilapia (Oreochromis niloticus) under Long-Term Alkalinity Stress

Alkalinity stress is the main stress experienced by aquatic animals in saline-alkali water, which hinders the aquaculture development and the utilization of water resources. The two-factor (2 × 3) test was adopted to study the influence of dietary protein to carbohydrate ratios on the energy metabolism of Nile tilapia (Oreochromis niloticus) under different alkalinity stress levels. Three diets with different protein-carbohydrate ratios (P27/C35, P35/C25, and P42/C15) were fed to fish cultured in freshwater (FW, 1.3 mmol/L carbonate alkalinity) or alkaline water (AW, 35.7 mmol/L carbonate alkalinity) for 50 days. Ambient alkalinity decreased tilapia growth performance. Although ambient alkalinity caused oxidative stress and enhanced ion transport and ammonia metabolism in tilapia, tilapia fed the P27/C35 diet showed better adaptability than fish fed the other two diets in alkaline water. Further metabolomic analysis showed that tilapia upregulated all the pathways enriched in this study to cope with alkalinity stress. Under alkalinity stress, tilapia fed the P27/C35 diet exhibited enhanced pyruvate metabolism and purine metabolism compared with tilapia fed the P42/C15 diet. This study indicated that ambient alkalinity could significantly decrease growth performance and cause oxidative stress and osmotic regulation. However, reducing dietary protein content by increasing carbohydrates could weaken stress and improve growth performance, ion transport, and ammonia metabolism in tilapia under long-term hyperalkaline exposure.

Effects of Bacillus halophilus on growth, intestinal flora and metabolism of Larimichthys crocea

The incorporation of probiotics into the diet of large yellow croaker has been demonstrated by several studies to confer partial disease resistance. Bacillus halophilic isolated from the intestinal flora was used to study its effects on performance growth indicators, intestinal tissue structure, intestinal flora and the metabolism of Larimichthys crocea. A total of 180 fishes with an initial body weight of (164.00 ± 54.00) g were fed diets with three different concentrations of Bacillus halophilic: 0 cfu/mL (FC0, control group), 108 cfu/mL (FC8, treatment group), and 1012 cfu/mL (FC12, treatment group). The results showed that there were no significant differences in specific growth rate among all groups (P > 0.05). Compared to the FC0 group, the final body weight and Weight gain rate were significantly higher in FC8 and FC12 groups (P < 0.05). The Survival of the FC12 group significantly improved (P < 0.05). Compared to the FC0 group, crude protein content in muscle of the FC8 group significantly increased (P < 0.05), crude fat content significantly increased in the FC12 group (P < 0.05), crude protein content in whole fish experimental groups significantly increased (P < 0.05), and ash content significantly increased in the FC8 group (P < 0.05). In terms of antioxidant ability, the content of LZM in blood increased significantly in the FC8 group (P < 0.05), GSH content in liver of the FC12 group increased significantly (P < 0.05), while the content of MDA and AKP in blood and liver had no significant difference (P > 0.05). At the level of intestinal structure, there were no significant differences in villus height, crypt depth and goblet cell number between control group and treatment groups (P > 0.05). At the phylum level, Firmicutes was the dominant phylum, and the genus level, Lactobacillus and Bacteroides were the dominant bacteria in FC8 and FC12. A total of 1070 metabolites were identified, among which lipid metabolites accounted for 46.7%. Metabolites were involved in six main ways, mainly related to the metabolism of amino acids and lipids. The correlation analysis between microbes and metabolites showed that the intestinal flora of Larimichthys crocea could promote the synthesis of metabolites, among which Bacteroides and Megamonas could promote the synthesis of beneficial metabolites such as amino acids and vitamins. Through this study, we found that Bacillus halophilic can significantly improve growth, the antioxidant immunity ability and promote the expression of growth related metabolites, with the FC12 group being the better successful.

Effects of Dietary Resveratrol, Bile Acids, Allicin, Betaine, and Inositol on Recovering the Lipid Metabolism Disorder in the Liver of Rare Minnow Gobiocypris rarus Caused by Bisphenol A

The fatty liver is one of the main problems in aquaculture. In addition to the nutritional factors, endocrine disrupter chemicals (EDCs) are one of the causes of fatty liver in fish. Bisphenol A (BPA) is a plasticizer widely used in the production of various plastic products and exhibits certain endocrine estrogen effects. Our previous study found that BPA could increase the accumulation of triglyceride (TG) in fish liver by disturbing the expression of lipid metabolism-related genes. How to recover the lipid metabolism disorder caused by BPA and other environmental estrogens remains to be explored. In the present study, Gobiocypris rarus was used as a research model, and 0.01% resveratrol, 0.05% bile acid, 0.01% allicin, 0.1% betaine, and 0.01% inositol were added to the feed of the G. rarus that exposed to 15 μg/L BPA. At the same time, a BPA exposure group without feed additives (BPA group) and a blank group with neither BPA exposure nor feed additives (Con group) were setted. The liver morphology, hepatosomatic index (HSI), hepatic lipid deposition, TG level, and expression of lipid metabolism-related genes were analyzed after 5 weeks of feeding. The HSI in bile acid and allicin groups was significantly lower than that in Con group. The TG in resveratrol, bile acid, allicin, and inositol groups returned to Con level. Principal component analysis of TG synthesis, decomposition, and transport related genes showed that dietary bile acid and inositol supplementation had the best effect on the recovery of BPA-induced lipid metabolism disorder, followed by allicin and resveratrol. In terms of lipid metabolism-related enzyme activity, bile acid and inositol were the most effective in recovering BPA-induced lipid metabolism disorders. The addition of these additives had a restorative effect on the antioxidant capacity of G. rarus livers, but bile acids and inositol were relatively the most effective. The results of the present study demonstrated that under the present dosage, bile acids and inositol had the best improvement effect on the fatty liver of G. rarus caused by BPA. The present study will provide important reference for solving the problem of fatty liver caused by environmental estrogen in aquaculture.