Growth and enterotoxin production of Staphylococcus aureus in shrimp

Identifying the function of the PI3K-AKT pathway during the pathogenic infection of Macrobrachium rosenbergii

The phosphoinositide-3-kinase/protein kinase b (PI3K-Akt) pathway is a signalling pathway based on protein phosphorylation and can be activated by a wide range of factors. To investigate the function of the PI3K-AKT signalling pathway in antibacterial immunity, we analysed the gene expression level of three key factors (PI3K, AKT and FoxO) and innate immune factors in immune tissues at different time points after Vibrio parahaemolyticus and Staphylococcus aureus infection. Tissues analysis showed that PI3K, AKT, and FoxO were expressed at high levels in the intestinal, hemocytes and hepatopancreas. Moreover, the expression levels of PI3K, AKT and FoxO can be regulated postinfection by different pathogens. In hemocytes and the intestine, V. parahaemolyticus infection was found to regulate the levels of PI3K, AKT, and FoxO more rapidly; however, an S. aureus infection regulated the levels of these factors more rapidly in the hepatopancreas and gills. Analysis showed that V. parahaemolyticus and S. aureus infection caused changes in the gene expression level of crustin, caspase 3 and NF-κB. Therefore, PI3K-AKT regulates the downstream immune pathway differentially in different immune tissues and participates in the regulation of cell apoptosis and the inflammatory response by activating caspase and NF-κB, respectively, following infection with V. parahaemolyticus and S. aureus.

Thymosin beta-4 participate in antibacterial immunity and wound healing in black tiger shrimp, Penaeus monodon

Thymosin beta-4 (Tβ4) is a ubiquitous protein with multiple and diverse intracellular and extracellular functions in vertebrates, which play fundamental roles in innate immune against pathogens and wound healing. In this study, the full-length cDNA of Tβ4 was cloned from Penaeus monodon (designated as PmTβ4), using the technology of rapid amplification of cDNA ends (RACE). The cDNA of PmTβ4 was 1361 bp with an open reading frame (ORF) of 501 bp, which encoding a polypeptide of 166 amino acid. The Quantitative Real-time PCR (qRT-PCR) analysis results showed that PmTβ4 was ubiquitously expressed in all the tested shrimp tissues, with the highest expression level was detected in the hemolymph, while the lowest expression level in the muscle. The expression level of PmTβ4 was significantly up-regulated in hepatopancreas after challenged by Vibrio parahaemolyticus, Vibrio harveyi and Staphylococcus aureus. In vitro antimicrobial test showed that the recombinant protein of PmTβ4 (rPmTβ4) had broad-spectrum of antimicrobial activity, which could inhibit both the growth of gram-negative bacteria and gram-positive bacteria, including Vibrio vulnificus, V. parahaemolyticus, Streptococcus agalactiae, S. aureus and Aeromonas hydrophila. Moreover, rPmTβ4 had a certain binding ability to different bacteria, and this binding ability exhibits a strong dose-dependent effect. In vivo, PmTβ4 could facilitate external bacterial clearance in shrimp, and have beneficial to shrimp survival post V. parahaemolyticus infection. Furthermore, wound-healing assay was carried out to study the role of PmTβ4 in the process of wound healing. The results showed that the PmTβ4 expression was significantly up-regulated by injury treatment, and exerted positive effects to promote wound healing. In addition, PmTβ4 can significantly increase the expression level of superoxide dismutase (SOD) and Catalase (CAT) after injury treatment in shrimp, which would involve in scavenging reactive oxygen species (ROS) caused by the wound. In conclusion, these results indicated that PmTβ4 may play important roles in antibacterial immunity and wound healing in Penaeus monodon.