Granulin peptide GRN-41 of Mozambique tilapia is a novel antimicrobial peptide against Vibrio species

Transcriptomic insights into the resistance mechanism of Penaeus vannamei against highly lethal Vibrio parahaemolyticus

Highly lethal Vibrio disease (HLVD) caused by a virulent strain of Vibrio parahaemolyticus (VpHLVD), which poses a significant threat to Penaeus vannamei post-larvae, leads to substantial mortality and economic losses. To address this challenge, researchers have recently isolated a highly disease-resistant strain of P. vannamei shrimp. However, the underlying mechanisms that could improve disease resistance require further investigation. Our study found that disease-resistant shrimp exhibited a remarkable ability to prevent VpHLVD invasion effectively. To unravel the genetic basis of this resistance, we conducted a transcriptomic analysis with susceptible and disease-resistant shrimp at various time points (0, 6, and 12 h) post-infection with VpHLVD. Differential gene expression (DEGs) analysis of uninfected shrimp revealed that disease-resistant individuals displayed higher expression of immune-related genes and pathways compared to their susceptible counterparts. Simultaneously, they exhibited lower expression of Vibrio toxin-binding genes and Vibrio colonization gene, indicating enhanced defense mechanisms in the resistant shrimp. Upon VpHLVD infection, DEGs analysis also showed that susceptible shrimp attempt to mount a similar immune response as the disease-resistant shrimp during the early stages of infection. However, as the infection progresses, the defense strategies diverge between the two groups, with the peak of gene response occurring later in the disease-resistant shrimp. Our findings indicated that disease-resistant shrimp did not experience significant stress during the early stages of infection and are capable of effectively enhancing their immune response in the middle and late stages of the infection. In summary, our study enhanced the understanding of the mechanisms employed by disease-resistant shrimp to combat Vibrio, and would help to develop effective strategies for disease prevention and control, ultimately reducing the impact of HLVD on shrimp aquaculture.

Animal granulins: In the GRN scheme of things

Granulins are conserved in nearly all metazoans, with an intriguing loss in insects. These pleiotropic peptides are involved in numerous physiological and pathological processes yet have been overwhelmingly examined in mammalian systems. While work in other animal models has been informative, a richer understanding of the proteins should be obtained by integrating knowledge from all available contexts. The main bodies of work described here include 1) the structure-function relationships of progranulin and its cleavage products, 2) the role of expanded granulin gene families and different isoforms in fish immunology, 3) the release of granulin peptides to promote host angiogenesis by parasitic worms, 4) a diversity of molluscan uses for granulins, including immune activation in intermediate hosts to trematodes, 5) knowledge gained on lysosomal functions from C. elegans and the stress-related activities of granulins. We provide an overview of functional reports across the Metazoa to inform much-needed future research.

Sensitization of KPC and NDM Klebsiella pneumoniae To Rifampicin by the Human Lactoferrin-Derived Peptide hLF1-11

A synergistic effect of non-bactericidal concentrations of the human lactoferrin (hLF)-derived peptide hLF1-11 and rifampicin against multidrug-resistant KPC (Klebsiella pneumoniae carbapenemase)-producing K. pneumoniae has been previously shown. The present study focuses on the mechanism(s) underlying this synergistic effect. The contribution of hLF1-11 and rifampicin to the synergistic effect was evaluated by killing assays with KPC K. pneumoniae cells incubated with hLF1-11 and, after washing, with rifampicin, or vice versa. Cell membrane permeability and polarization upon exposure to hLF1-11 and/or rifampicin were evaluated by ethidium bromide (EtBr) and DiBAC₄(3) (bis-1,3-dibutylbarbituric acid trimethine oxonol) permeability, respectively. The effect of carbonyl cyanide m-chlorophenyl hydrazone (CCCP), an uncoupler of oxidative phosphorylation, was also evaluated. KPC K. pneumoniae cells were effectively killed after prior exposure to rifampicin for 30 to 60 min followed by treatment with hLF1-11, while no antibacterial activity was observed when cells were incubated with hLF1-11 first and then with rifampicin. EtBr accumulation increased upon exposure to hLF1-11 or the combination of hLF1-11 and rifampicin, but not upon exposure to rifampicin alone. Moreover, hLF1-11 induced a dose-dependent membrane depolarization. As expected, the antibacterial activity of hLF1-11 alone or combined with rifampicin was significantly reduced in the presence of CCCP. Furthermore, hLF1-11 and rifampicin were synergistic also against a colistin-resistant NDM (New Delhi metallo-β-lactamase)-producing K. pneumoniae strain. The results suggest that rifampicin was accumulated by KPC cells during the 30-to-60-min incubation and that the addition of hLF1-11 sensitized bacterial cells to rifampicin by inducing a transient loss of membrane potential and increased cell membrane permeability, thus facilitating the entrance and retention of rifampicin into the cytoplasm. IMPORTANCE The present study describes a synergistic effect between rifampicin, an impermeable hydrophobic antibiotic with an intracellular target, and an hLF1-11, an antimicrobial peptide derived from human lactoferrin, against multidrug-resistant Klebsiella pneumoniae. Carbapenem-resistant K. pneumoniae has recently caused an outbreak in Tuscany, Italy, thus pressing the need for the development of new treatment options. The mechanisms underlying such a synergistic effect have been studied. The results suggest that the synergistic effect was due to the transient loss of membrane potential induced by hLF1-11 and the subsequent increase in cell membrane permeability which allowed rifampicin to enter the bacterial cell. Therefore, it is likely that a sub-inhibitory concentration of hLF1-11 can efficiently permeabilize K. pneumoniae cells to rifampicin, allowing the antibiotic to reach its intracellular target. These results encourage further exploration of possible applications of this synergistic combination in the treatment of K. pneumoniae infections.

Development of Disease-Resistance-Associated Microsatellite DNA Markers for Selective Breeding of Tilapia (Oreochromis spp.) Farmed in Taiwan

There are numerous means to improve the tilapia aquaculture industry, and one is to develop disease resistance through selective breeding using molecular markers. In this study, 11 disease-resistance-associated microsatellite markers including 3 markers linked to hamp2, 4 linked to hamp1, 1 linked to pgrn2, 2 linked to pgrn1, and 1 linked to piscidin 4 (TP4) genes were established for tilapia strains farmed in Taiwan after challenge with Streptococcus inae. The correlation analysis of genotypes and survival revealed a total of 55 genotypes related to survival by the chi-square and Z-test. Although fewer markers were found in B and N2 strains compared with A strain, they performed well in terms of disease resistance. It suggested that this may be due to the low potency of some genotypes and the combinatorial arrangement between them. Therefore, a predictive model was built by the genotypes of the parental generation and the mortality rate of different combinations was calculated. The results show the same trend of predicted mortality in the offspring of three new disease-resistant strains as in the challenge experiment. The present findings is a nonkilling method without requiring the selection by challenge with bacteria or viruses and might increase the possibility of utilization of selective breeding using SSR markers in farms.

Comparative transcriptome analysis reveals ectopic delta-5 and delta-6 desaturases enhance protective gene expression upon Vibrio vulnificus challenge in Tilapia (Oreochromis niloticus)

Background

Tilapia (Oreochromis niloticus) cultures are frequently infected by Vibrio vulnificus, causing major economic losses to production units. Previously, tilapia expressing recombinant delta-5 desaturase and delta-6 desaturase (D56) were found to be resistant to V. vulnificus infection. In this report, we profile the D56-mediated molecular changes underlying this resistance in tilapia. A comparative transcriptome analysis was performed on V. vulnificus-infected wild-type and D56-transgenic tilapia using Illumina’s sequencing-by-synthesis approach. Gene enrichment analysis on differentially expressed unigenes was performed, and the expression patterns were validated by real-time PCR.

Results

Comparative transcriptome analysis was performed on RNA-sequence profiles obtained from wild-type and D56-transgenic tilapia at 0, 6 and 24 h post-infection with V. vulnificaus. GO and KEGG gene enrichment analyses showed that D56 regulates several pathways and genes, including fatty acid (FA) metabolism associated, and inflammatory and immune response. Expression of selected FA metabolism-associated, inflammatory and immune responsive genes was validated by qPCR. The inflammatory and immune responsive genes that are modulated by FA-associated D56 likely contribute to the enhanced resistance against V. vulnificus infection in Tilapia.

Conclusions

Transcriptome profiling and filtering for two-fold change variation showed that 3795 genes were upregulated and 1839 genes were downregulated in D56-transgenic tilapia. These genes were grouped into pathways, such as FA metabolism, FA elongation, FA biosynthesis, biosynthesis of unsaturated FA, FA degradation, inflammation, immune response, and chemokines. FA-associated genes and immune-related genes were modulated by D56 at 6 h and 24 h post infection with V. vulnificus. The expression patterns of FA-related genes, inflammatory genes, antimicrobial peptide genes and immune responsive genes at 0, 3, 6, 12, 24 and 48 h post-infection suggests these genes are involved in the enhanced resistance of D56 transgenic tilapia to V. vulnificus.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07521-5.

Improved Stability and Activity of a Marine Peptide-N6NH2 against Edwardsiella tarda and Its Preliminary Application in Fish

Edwardsiella tarda can cause fatal gastro-/extraintestinal diseases in fish and humans. Overuse of antibiotics has led to antibiotic resistance and contamination in the environment, which highlights the need to find new antimicrobial agents. In this study, the marine peptide-N6 was amidated at its C-terminus to generate N6NH2. The antibacterial activity of N6 and N6NH2 against E. tarda was evaluated in vitro and in vivo; their stability, toxicity and mode of action were also determined. Minimal inhibitory concentrations (MICs) of N6 and N6NH2 against E. tarda were 1.29–3.2 μM. Both N6 and N6NH2 killed bacteria by destroying the cell membrane of E. tarda and binding to lipopolysaccharide (LPS) and genomic DNA. In contrast with N6, N6NH2 improved the stability toward trypsin, reduced hemolysis (by 0.19% at a concentration of 256 μg/mL) and enhanced the ability to penetrate the bacterial outer and inner membrane. In the model of fish peritonitis caused by E. tarda, superior to norfloxacin, N6NH2 improved the survival rate of fish, reduced the bacterial load on the organs, alleviated the organ injury and regulated the immunity of the liver and kidney. These data suggest that the marine peptide N6NH2 may be a candidate for novel antimicrobial agents against E. tarda infections.

Epinecidin-1: An orange-spotted grouper antimicrobial peptide that modulates Staphylococcus aureus lipoteichoic acid-induced inflammation in macrophage cells

Orange-spotted grouper (Epinephelus coioides) is among the most economically important of all fish species farmed in Asia. This species expresses an antimicrobial peptide called epinecidin-1 (EPI), which is considered to be a host defense factor due to its strong bacterial killing activity. Antimicrobial peptides usually possess both bacterial killing and immunomodulatory activity, however, the modulatory activity of EPI on Gram-positive bacterial lipoteichoic acids (LTA)-induced inflammation has not been previously reported. In this study, we found that EPI effectively suppressed LTA-induced production of proinflammatory factors in macrophages. Mechanistically, EPI attenuated LTA-induced inflammation by inhibiting Toll-like receptor (TLR) 2 internalization and subsequent downstream signaling (reactive oxygen species, Akt, p38 and Nuclear factor κB). However, protein abundance of TLR2 was not altered by EPI or LTA. Taken together, our findings reveal for the first time that EPI possesses inhibitory activity toward LTA-induced inflammation in macrophages.