Effects of 5-Aminolevulinic Acid on Gene Expression, Immunity, and ATP Levels in Pacific White Shrimp, Litopenaeus vannamei

Effects of dietary 5-aminolevulinic acid on growth performance and nonspecific immunity of Litopenaeus vannamei, as determined by transcriptomic analysis

5-aminolevulinic acid (5-ALA) is an endogenous non-protein amino acid that is frequently used in modern agriculture. This study set out to determine how dietary 5-ALA affected the nonspecific immunity and growth performance of Litopenaeus vannamei. The shrimp were supplemented with dietary 5-ALA at 0, 15, 30, 45, and 60 mg/kg for three months. Transcriptome data of the control group and the group supplemented with 45 mg/kg dietary 5-ALA were obtained using transcriptome sequencing. 592 DEGs were identified, of which 426 were up-regulated and 166 were down-regulated. The pathways and genes associated with growth performance and nonspecific immunity were confirmed using qRT-PCR. The highest survival rate, body length growth rate, and weight gain values were observed in shrimp fed diets containing 45 mg/kg 5-ALA. L. vannamei in this group had a significantly higher total hemocyte count, phagocytosis rate and respiratory burst value than those in the control group. High doses of dietary 5-ALA (45 mg/kg, 60 mg/kg) significantly increased the activities of catalase, superoxide dismutase, oxidized glutathione, glutathione-peroxidase, phenoloxidase, lysozyme, acid phosphatase, and alkaline phosphatase. At the transcriptional level, dietary 5-ALA significantly up-regulated the expression levels of antioxidant immune-related genes. The optimal concentration of 5-ALA supplementation was 39.43 mg/kg, as indicated by a broken line regression. Our study suggested that dietary 5-ALA positively impacts the growth and nonspecific immunity of L. vannamei, providing a novel theoretical basis for further research into 5-ALA as a dietary supplement.

Analysis of microbiota in the stomach and midgut of two penaeid shrimps during probiotic feeding

In mammals, the intestine harbors numerous bacteria that play an important role in health. Intestinal microbiota have also been thought to be an important factor in the health of shrimp. However, the barrier systems of the digestive tracts of shrimp seem to be different from those of mammals. In this study, we analyzed the bacterial composition in the stomach and midgut of two species of shrimp during administration of a probiotic, Bacillus amyloliquefaciens strain TOA5001 by analysis of 16S rRNA genes with Illumina sequencing technology. Whiteleg shrimp Litopenaeus vannamei were observed under laboratory conditions and kuruma shrimp Marsupenaeus japonicus were observed in an aquaculture farm. The diversities of bacteria in the stomachs of both shrimps were significantly higher than those in the midgut. Also, the microbiota changed during probiotic feeding. Feeding whiteleg shrimp the probiotic after being challenged with an acute hepatopancreatic necrosis disease (AHPND)-causing strain of Vibrio parahaemolyticus increased their survival compared to the control group, which suggested that the probiotic prevented AHPND. These results appear to show that a probiotic can affect the microbiota throughout digestive tract of penaeid shrimps and that probiotic can have a role in preventing disease.

Nuclear receptor E75 is a transcription suppressor of the Litopenaeus vannamei small subunit hemocyanin gene

Hemocyanin is a respiratory protein that possesses multiple physiological and immunological functions in shrimp. However, the transcriptional regulation of the hemocyanin gene is still poorly understood. Here, the nuclear receptor E75 of Litopenaeus vannamei (LvE75) was identified as one of the transcriptional regulators that modulates the transcription of the small molecular weight hemocyanin gene of L. vannamei (LvHMCs) by inhibiting its core promoter activity in a Dual-luciferase assay. In silico analysis revealed that the core promoter (designated HsP3), which is located at +1517/+1849 bp of LvHMCs contained a putative E75 binding motif ("ACGGAAT", spanning +1812/+1818 bp). Further, LvE75 was shown to inhibit the core promoter activity by direct binding. Importantly, in vivo silencing of LvE75 resulted in a significant upregulation in the mRNA and protein expression of LvHMCs gene. Taken together, our present results provide direct evidence that LvE75 is a transcriptional suppressor of the LvHMCs gene expression.

Molecular cloning, characterization and gene expression analysis of aminolevulinic acid synthase in Litopenaeus vannamei

5-Aminolevulinic acid synthase (ALAS) is the rate-limiting enzyme in the biosynthesis of heme, a prosthetic group that is found in hemoproteins, including those involved in molting. To better understand the roles of ALAS in L. vannamei (LvALAS), we analyzed its sequence and tissue distribution, the effects of age and bacterial infection on its gene expression, and the effects of LvALAS gene silencing. We also examined the expressions of three hemoproteins, the cytochrome oxidase subunit I (COX I) and subunit IV (COX IV) and catalase. Three LvALAS splicing variants were found in the hepatopancreas, with the main splicing variant having an open reading frame that encodes 532 aa. LvALAS transcripts were found in each of the eleven tissues tested in this study, with the highest gene expression in the intestine. The transcript abundances of LvALAS, COX I and COX IV in the hepatopancreas and stomach tended to decrease with age. LvALAS and catalase gene expressions significantly increased in the stomach after V. parahaemolyticus infection. LvALAS gene expression in the hepatopancreas, stomach and intestine (12- and 24-hours post-injection) was relatively lower in dsALAS-injected shrimp than in PBS-injected shrimp. All the PBS-injected shrimp molted after 8-10 days while no molting activity was observed in the dsALAS-injected shrimp group within the 14 days post-injection period. Our results provide evidence that (1) only the housekeeping form of ALAS exists in L. vannamei; LvALAS gene expression (2) decreases with age and (3) increases after bacterial infection; and (4) an ALAS-dependent pathway is necessary for proper molting in L. vannamei.