Antibacterial activity and immunomodulatory role of a proline-rich antimicrobial peptide SpPR-AMP1 against Vibrio campbellii infection in shrimp Litopenaeus vannamei

Scorpion venom peptides enhance immunity and survival in Litopenaeus vannamei through antibacterial action against Vibrio parahaemolyticus

Introduction

Scorpion venom-derived antimicrobial peptides (AMPs) have emerged as promising candidates for combating bacterial infections owing to their potent activity and unique mechanisms of action. This study focuses on three 13-amino-acid peptides-BmKn1, BmKn2, and BmKn2-7-derived from the venom of Mesobuthus martensii. The aim is to elucidate their structural features, antibacterial efficacy, and immunomodulatory effects in Litopenaeus vannamei infected with Vibrio parahaemolyticus (VP).

Methods

The peptides were synthesized and comprehensively characterized for their amphipathic α-helical structures, net charges, and hydrophobicity. Their antibacterial mechanisms were investigated using a series of assays, including membrane permeability (inner/outer membrane disruption), membrane depolarization, reactive oxygen species (ROS) quantification, and ATPase activity measurement. In vivo challenge experiments were conducted to evaluate survival rates in L. vannamei infected with VP. Additionally, immune enzyme activities (phenoloxidase [PO], complement component 3 [C3]) and inflammatory/antimicrobial gene expression levels (TNF-α, IL-1β, TGF-β, ALF, Crus) were analyzed. Furthermore, intestinal transcriptome profiling was performed to identify the activated immune pathways.

Results

All peptides exhibited membrane-targeting activity: BmKn2-7 showed superior outer membrane penetration and depolarization, while BmKn1 was more effective in inner membrane disruption and ROS induction. In vivo, all peptides significantly improved survival rates in VP-infected shrimp (P < 0.01), with BmKn2-7 ≈ BmKn1 > BmKn2 in efficacy. Immune modulation was evident through increased PO and C3 activity (P < 0.05) and reduced expression of inflammatory cytokines and antimicrobial genes (P < 0.05). Transcriptome analysis revealed BmKn2-7 activated PPAR, AMPK, and FoxO signaling pathways.

Discussion

The amphipathic α-helical structure of these peptides is fundamental to their membrane-disruptive activity. The enhanced outer membrane targeting of BmKn2-7 likely correlates with structural modifications that optimize hydrophobicity and charge distribution. The differential efficacy in immune regulation, such as BmKn2-7's broad pathway activation versus BmKn1's selective ROS induction, indicates structure-dependent functional divergence. These findings highlight the potential of tailored scorpion venom peptides as dual-action agents against bacterial infections and immune dysregulation.

Hydrogel-antimicrobial peptide association: A novel and promising strategy to combat resistant infections

Infections from multi-drug resistant bacteria (MDRB) have raised a worldwide concern, with projections indicating that fatalities from these infections could surpass those from cancer by 2050. This troubling trend is influenced by several factors, including the scarcity of new antibiotics to tackle challenging infections, the prohibitive costs of last-resort antibiotics, the inappropriate use of antimicrobial agents in agriculture and aquaculture, and the over-prescription of antibiotics in community settings. One promising alternative treatment is the application of antimicrobial peptides (AMPs) against MDRB. Hydrogels can facilitate the delivery of these antimicrobials, enhancing their biocompatibility and bioavailability. The Peptide-Hydrogel Association (PHA) capitalizes on the distinct properties of both peptides and hydrogels, resulting in multifunctional systems suitable for various antibacterial purposes. Multiple strategies can be employed to develop a PHA, including peptide-based hydrogels, hydrogels infused with peptides, and hydrogels modified with peptide functionalities. The research examined in this review showcases the strong effectiveness of these systems against MDRB and underscores their potential in creating multifunctional and multi-responsive solutions for various infection scenarios. The high efficacy of PHAs represents a promising and innovative therapeutic strategy in combating infections caused by MDRB.

Effects of dietary supplementation with Bacillus velezensis on the growth performance, body composition, antioxidant, immune-related gene expression, and histology of Pacific white shrimp, Litopenaeus vannamei

In recent decades, probiotics have become an acceptable aquaculture strategy for shrimp growth promotion and immune modulation. This study aimed to evaluate the effect of Bacillus velezensis on Litopenaeus vannamei following a 60-day trial. L. vannamei (3 ± 0.4 g) were distributed into four groups with three replicates per group and fed an isonitrogenous diet supplemented with B. velezensis at 0, 1 × 107, 1 × 108, and 1 × 109 CFU/g, which were defined as the control, G1, G2, and G3 groups, respectively. B. velezensis significantly improved the growth, survival rate, and proximate body composition of L. vannamei (P < 0.05). All groups fed the B. velezensis diet showed significant increases in digestive enzymes (lipase, amylase, and protease), superoxide dismutase (SOD; G3), catalase (CAT; G3, G2, and G1), lysozyme activity (G3 and G2), immunoglobulin M (IgM), bactericidal activity BA%, alkaline phosphatase (AKP), and acid phosphatase (ACP) compared with the control group (P < 0.05). Malondialdehyde (MDA), triglycerides, cholesterol, high-density lipoprotein (HDL), low-density lipoprotein (LDL), aspartate aminotransferase (AST), and alanine aminotransferase (ALT) levels were significantly decreased in all groups fed B. velezensis diet compared with the control group (P < 0.05). The expression levels of SOD (G3), LZM, and serine proteinase genes were significantly higher in L. vannamei fed diets containing B. velezensis than in the control group (P < 0.05). This is the first study to address the effects of B. velezensis on the expression of the LZM and serine proteinase genes in L. vannamei. L. vannamei fed diet containing B. velezensis had more B and R cells in its hepatopancreas than did the control group. In conclusion, B. velezensis is a promising probiotic that can be safely added to the diet of L. vannamei with 1 × 109 CFU/g. Its application had a positive influence on the health status, survival rate, nutritional value, and immunity of L. vannamei.