Cloning and expression analysis of c-type and g-type lysozymes in yellow catfish (Pelteobagrus fulvidraco)

Uncovering the antimicrobial activity of G-type lysozyme 2 derived from Cyprinus carpio mucus against bacterial and fungal pathogens

This study aimed to explore the antimicrobic potential of mucus samples collected from Cyprinus carpio and identify the specific antimicrobial peptides responsible for its activity. The crude extract was tested against various bacterial and fungal pathogens, and its protein content and profile were analyzed. Purification steps, including gel filtration chromatography, were employed to isolate the most active fraction (peak IV), which was further identified via liquid chromatography and mass spectroscopy. The results revealed varying degrees of antimicrobial activity of the crude extract against different bacterial and fungal strains, with Leclercia adecarboxylata, Candida glabrata, and Candida parapsilosis showing the highest susceptibility. SDS-PAGE analysis demonstrated the existence of multiple low molecular weight protein bands in the crude extract, while fraction IV obtained from gel filtration chromatography exhibited the strongest antimicrobial activity. Peak IV displayed a range of minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and minimum fungicidal concentration (MFC) values against the tested pathogens, spanning from 0.038 to 4.960 mg/mL. Further investigation identified the purified peptide derived from peak IV as G-type lysozyme 2, characterized by a molecular weight of 21 kDa. These findings shed light on the existence of a highly effective antimicrobial peptide, G-type lysozyme 2, within the mucus of Cyprinus carpio. This peptide demonstrates notable activity against diverse bacterial and fungal pathogens. The insights from this study enhance our understanding of the fish's antimicrobial defense mechanisms and hold promise for developing novel antimicrobial agents.

Molecular characterization and antibacterial activities of a goose-type lysozyme gene from roughskin sculpin (Trachidermus fasciatus)

Lysozymes, acting as antimicrobial molecules, play a vital role in the host's innate immune response to pathogen infections. In the present study, a g-type lysozyme gene termed Tf-LyzG from roughskin sculpin, Trachidermus fasciatus was firstly reported. The deduced amino acid sequence of Tf-LyzG contained 188 residues and possessed conserved catalytic residues (Glu⁷¹, Asp⁸⁴, and Asp⁹⁵). Gene expression analysis revealed that Tf-LyzG was widely distributed in the tested eleven tissues with the highest expression in the gill and could be significantly induced post lipopolysaccharide (LPS) challenge. The lysozyme activity of the purified recombinant protein (rTf-LyzG) was found to be most active at pH 5.5 and 37 °C. rTf-LyzG exhibited a wide spectrum of potent bacteriolytic activity against four Gram-positive bacteria and six Gram-negative bacteria. It also displayed a high affinity to polysaccharides on bacteria surfaces including LPS, lipoteichoic acid (LTA), and peptidoglycan (PGN). rTf-LyzG was capable of binding and agglutinating all nine bacteria. Flow cytometry assay further revealed that rTf-LyzG could disrupt the membrane of Micrococcus lysodeikticus which is confirmed by scanning electron microscope (SEM) analysis that reveals blebs around the bacterial cell membrane. In summary, these data indicate that Tf-LyzG is of great importance in the fish immune response against pathogens invasion.

Effect of dietary isoleucine on skin mucus barrier and epithelial physical barrier functions of hybrid bagrid catfish Pelteobagrus vachelli × Leiocassis longirostris

The study investigated the effects of dietary isoleucine (Ile) on skin mucus barrier and epithelial physical barrier functions of hybrid bagrid catfish Pelteobagrus vachelli × Leiocassis longirostris. A total of 630 fish (33.11 ± 0.09 g) were fed semi-purified isonitrogenous diets containing 5.0 (control), 7.5, 10.0, 12.5, 15.0, 17.5, and 20.0 g Ile kg ^-1 diet for 8 weeks. The results indicated that dietary Ile increased (P < 0.05) in skin (1) mucus protein content and antimicrobial activity against three gram-negative bacteria (Aeromonas hydrophila, Escherichia coli, and Yersinia ruckeri) and two gram-positive bacteria (Streptococcus agalactiae and Staphylococcus aureus), (2) mucus lysofew information is available about the influencezyme (LZM), acid phosphatase (ACP), and alkaline phosphatase (AKP) activities, and complement 3 and 4 (C3 and C4) and immunoglobulin M (IgM) contents, (3) intelectin 1 (intl1), intelectin 2 (intl2), c-type-lysozyme (c-LZM), g-type-lysozyme (g-LZM), and β-defensin mRNA levels. Dietary Ile decreased (P < 0.05) reactive oxygen species (ROS), malondialdehyde (MDA), and protein carbonyl (PC) contents, and up-regulated (P < 0.05) CuZnSOD, GST, GPX1a, muc5ac, muc5b, zonula occludens-1 (ZO-1), zonula occludens-2 (ZO-2), occludin, and claudin 3 mRNA levels in skin. These results indicated that Ile improved skin mucus barrier function via increasing mucus protein, C3 and C4, and IgM contents and antibacterial factors activities, and promoted epithelial physical barrier function via decreasing skin antioxidant damage and improving tight junction structure in hybrid bagrid catfish.