Pathogens In Aquaculture Research Articles

New perspectives on metagenomic analysis for pathogen monitoring in sustainable freshwater aquaculture production: a systematic review

The freshwater and saltwater aquatic food sector has experienced the most significant growth in recent years and is increasingly recognized as a sustainable alternative for fostering prosperous societies self-sufficiently and ecologically. One primary economic and health risk factor in aquaculture production is health control, with potentially more severe impacts observed in tropical and developing countries. While metagenomics holds great promise for application in agro-industrial fields like aquaculture, its adoption remains limited. Consequently, this study aimed to assess the prospects for developing and applying metagenomics in identifying pathogens in freshwater aquaculture. The WIPO database was used to search for patents developed using metagenomics to monitoring pathogens in freshwater aquaculture. Metagenomics methods have been extensively employed in different fields, such as, medicine, veterinary, biotechnology, agriculture, particularly in studies focusing on microbial communities in different ecosystems. In aquaculture, the utilization of metagenomics has predominantly revolved around investigating antibiotic resistance genes, primarily in saltwater farms. Despite this, freshwater aquaculture, particularly in fish and crustacean farming, aligns closely with sustainable development goals, notably (SDGs) 2, 3, 6, and 13. Countries such as the United States of America, South Korea, and Canada stand at the forefront of utilizing metagenomics for disease monitoring in freshwater aquaculture, evidenced by their active patent developments. The metagenomic analysis, coupled with bioinformatics tools and databases, represents a rapid, secure, and non-invasive approach to environmental monitoring for preventive purposes.Systematic review registrationhttps://osf.io/srpyz/, identifier 10.17605/OSF.IO/SRPYZ.

Antibiofilm activity of Morganella morganii JB8F and Pseudomonas fluorescens JB3B compound to control single and multi-species of aquaculture pathogens

BackgroundIndonesia is a country that uses half or more aquatic foods as protein intake. The increased production in aquaculture industries might cause several problems, such as bacterial disease resulting in mass mortality and economic losses. Antibiotics are no longer effective because aquaculture pathogens can form biofilm. Biofilm is a microbial community that aggregates and firmly attaches to living or non-living surfaces. Biofilm formation can be caused by environmental stress, the presence of antibiotics, and limited nutrients. Therefore, it is important to explore antibiofilm to inhibit biofilm formation and/or eradicate mature biofilm. Phyllosphere bacteria can produce bioactive compounds for antimicrobial, antibiofilm, and anti-quorum sensing. Three aquaculture pathogens were used in this study, such as Aeromonas hydrophila, Streptococcus agalactiae, and Vibrio harveyi.ResultsPseudomonas fluorescens JB3B and Morganella morganii JB8F extracts could disrupt single and multi-species biofilms. Both extracts could inhibit single biofilm formation from one to seven days of incubation time. We confirmed the destruction activity on multi-species biofilm using light microscope and scanning electron microscope. Using GC-MS analysis, indole was the most active fraction of the P. fluorescens JB3B extracts and octacosane from the M. morganii JB8F extract. We also conducted a toxicity test using brine shrimp lethality assay on P. fluorescens JB3B and M. morganii JB8F extracts. P. fluorescens JB3B, M. morganii JB8F, and a mixture of both extracts were confirmed non-toxic according to the LC50 value of the brine shrimp lethality test.ConclusionsP. fluorescens JB3B and M. morganii JB8F phyllosphere extracts had antibiofilm activity to inhibit single biofilm and disrupt single and multi-species biofilm of aquaculture pathogens. Both extracts could inhibit single species biofilm until seven days of incubation. Bioactive compounds that might contribute to antibiofilm properties were found in both extracts, such as indole and phenol. P. fluorescens JB3B, M. morganii JB8F extracts, and mixture of both extracts were non-toxic against Artemia salina.

Modulation of the unfolded protein response by white spot syndrome virus via wsv406 targeting BiP to facilitate viral replication

Outbreaks of diseases are often linked to environmental stress, which can lead to endoplasmic reticulum (ER) stress and subsequently trigger the unfolded protein response (UPR). The replication of the white spot syndrome virus (WSSV), the most serious pathogen in shrimp aquaculture, has been shown to rely on the UPR signaling pathway, although the detailed mechanisms remain poorly understood. In this study, we discovered that WSSV enhances its replication by hijacking the UPR pathway via the viral protein wsv406. Our analysis revealed a significant upregulation of wsv406 in the hemocytes and gills of infected shrimp. Mass spectrometry analysis identified that wsv406 interacts specifically with the immunoglobulin heavy-chain-binding protein (BiP) in shrimp Litopenaeus vannamei. Further examination revealed that wsv406 binds to multiple domains of LvBiP, inhibiting its ATPase activity without disrupting its binding to UPR stress receptors. Silencing either wsv406 or LvBiP resulted in a reduction in WSSV replication and improved shrimp survival rates. Further, wsv406 activation of the PRKR-like ER kinase (PERK)-eukaryotic translation initiation factor 2α (eIF2α) and activating transcription factor 6 (ATF6) pathways was demonstrated by a decrease in the phosphorylation of eIF2α and the nuclear translocation of ATF6 when wsv406 was silenced during WSSV infection. This activation facilitated the transcription of WSSV genes, promoting viral replication. In summary, these findings reveal that wsv406 manipulates the host UPR by targeting LvBiP, thereby enhancing WSSV replication through the PERK-eIF2α and ATF6 pathways. These insights into the interaction between WSSV and host cellular machinery offer potential targets for developing therapeutic interventions to control WSSV outbreaks in shrimp aquaculture.

Impact of plasma treatment of Au electrodes on response of EIS biosensors used in aquaculture pathogen detection

This study examines the effect of plasma treatment on gold electrodes used in construction of biosensors. Plasma treatment aims to improve the adhesion of bioreceptor layers, enhancing sensor performance. Gold substrates were exposed to plasma for different durations, and their reactivity was analyzed using electrochemical impedance spectroscopy (EIS), atomic force microscopy (AFM), and scanning electron microscopy (SEM). Results show that plasma treatment significantly enhances the hydrophilicity of gold surfaces, leading to better formation of bioreceptor layer. Optimal treatment duration was found to be around 60 s, beyond which improvements in impedance values diminished. Plasma-treated electrodes displayed superior bioreceptor adhesion without altering surface topography. In conclusion, plasma treatment improves biosensor performance by enhancing bioreceptor layer adhesion. Integrating this process into biosensor production can lead to more efficient and reliable pathogen detection in aquaculture, promoting healthier aquatic environments and sustainable food production.

Droplet digital PCR for fish pathogen detection and quantification: A systematic review and meta-analysis.

This study provides a comprehensive summary of the findings regarding the application and diagnostic efficacy of droplet digital PCR (ddPCR) in detecting viral and bacterial pathogens in aquaculture. Utilizing a systematic search of four databases up to 6 November 2023, we identified studies where ddPCR was deployed for pathogen detection in aquaculture settings, adhering to Preferred Reporting Items for Systematic Reviews and Meta-analysis of Diagnostic Test Accuracy guidelines. From the collected data, 16 studies retrieved, seven were included in a meta-analysis, encompassing 1121 biological samples from various fish species. The detection limits reported ranged markedly from 0.07 to 34 copies/μL. A direct comparison of the diagnostic performance between ddPCR with quantitative PCR (qPCR) proved challenging due to limited data, thus only a pooled sensitivity analysis was feasible. The results showed a pooled sensitivity of 0.750 (95% confidence interval [CI]: 0.487-0.944) for ddPCR, compared to 0.461 (95% CI: 0.294-0.632) for qPCR, with no statistically significant difference in sensitivity between the two methods (p = .5884). Notably, significant heterogeneity was observed among the studies (I2 = 93%-97%, p < .01), with the year of publication significantly influencing this heterogeneity (p < .001), but not the country of origin (p = .49). No publication bias was detected, and the studies generally exhibited a low risk of bias according to QUADAS-C criteria. While ddPCR and qPCR showed comparable sensitivities in pathogen detection, ddPCR's capability to precisely quantify pathogens without the need for standard curves highlights its potential utility. This characteristic could significantly enhance the accuracy and reliability of pathogen detection in aquaculture.

Epinecidin-1 and lactic acid synergistically inhibit Aeromonas hydrophila through membrane disruption

Epinecidin-1 (Epi-1) is an antimicrobial peptide originated from fish with various pharmacological activities but carries the risk of acquiring resistance with long-term use. In the present study, we use L-lactic acid to enhance the antibacterial activity of synthesized Epi-1 against the aquaculture and food pathogen Aeromonas hydrophila. The results showed that 5.5 mmol/L lactic acid increased the inhibitory and bactericidal activity of 25 μmol/L Epi-1 against two strains of A. hydrophila. The laser confocal images proved that lactic acid pre-treatment improved the attachment efficiency of Epi-1 in A.hydrophila cells. In addition, lactic acid enhanced the damaging effect of Epi-1 on the cell membrane of A. hydrophila, evidenced by releasing more nucleic acids, proteins, and transmembrane pH ingredients decrease and electromotive force dissipation. SEM images showed that compared with the single Epi-1 treatment, the co-treatment of Epi-1 and lactic acid caused more outer membrane vesicles (OMVs) and more severe cell deformation. These findings proved that lactic acid could enhance the efficiency of Epi-1 against A. hydrophila and shed light on new aspects to avoid resistance of pathogens against Epi-1.

Shewanella putrefaciens as an emerging pathogen of hepatopancreas necrosis disease in Chinese mitten crab Eriocheir sinensis.

Shewanella putrefaciens has been recognized as an emerging important pathogen in aquaculture. However, scarce information is available on the characterization and microbial control of S. putrefaciens as a causal agent of hepatopancreas necrosis disease in Chinese mitten crab Eriocheir sinensis. In this study, a multi-resistant S. putrefaciens isolate (DZ-A) was identified as a causal pathogen of hepatopancreas necrosis disease in Chinese mitten crabs. It showed a lethal dose (LD50) of 2.20 × 105 CFU ml-1 in Chinese mitten crabs, and multiple resistance to aminoglycoside, chloramphenicol, macrolide, penicillin, peptide, and tetracycline antimicrobials. In addition, Bdellovibrio powder exhibited a significant antibacterial effect against the pathogenic S. putrefaciens, and conferred significant protection to challenged Chinese mitten crabs with relative percentage survivals of 80.00% to 93.33% via significant improvement in their immune response and antioxidant capability. The findings of this study provide valuable insights into the phenotypic characterization and biological control of pathogenic S. putrefaciens in Chinese mitten crabs.

Assessment of dietary yeast-based additives for cultured catfish and tilapia health.

Channel catfish (Ictalurus punctatus) and Nile tilapia (Oreochromis niloticus) are two aquaculture species of great importance. Intensive production is often hindered by poor growth performance and disease mortality. The aim of this study was to evaluate the potential of a commercial fermented yeast product, DVAQUA, on channel catfish and Nile tilapia growth performance metrics and disease resistance. Channel catfish and Nile tilapia were fed practical diets supplemented with 0%, 0.1% or 0.4% of DVAQUA over approximately 2-month feeding periods in recirculation aquaculture systems. To assess the potential of the postbiotic against common aquaculture pathogens, juvenile catfish were subsequently challenged by immersion with Edwardsiella ictaluri S97-773 or virulent Aeromonas hydrophila ML09-119. Nile tilapia juveniles were challenged by injection with Streptococcus iniae ARS-98-60. Serum lysozyme activity, blood chemistry and growth metrics were measured at the end of the feeding period, but no differences were observed across the different metrics, except for survival. For the pathogen challenges, there were no differences in endpoint mortality for channel catfish with either pathogen (p > .05). In contrast, Nile tilapia survivability to S. iniae infection increased proportionally to the inclusion of DVAQUA (p = .005). Changes to sera lysozyme activity were also noted in the tilapia trial, with a reduction of activity in the fish fed the 0.4% DVAQUA diet compared to the control diet (p = .031). Expression profiles of proinflammatory genes and antibodies were also found to be modulated in channel catfish fed the postbiotic, indicating some degree of protective response. These results suggest that this postbiotic may be beneficial in protecting Nile tilapia against S. iniae infection by influencing immune parameters and additional research is needed to evaluate the potential of this DVAQUA for improving catfish health and disease control.

Evaluation of the antibacterial activity of pineapple (Ananas comosus) (L.) Merr. industrial waste against common fish and shellfish pathogens

Disposal of industrial pineapple (Ananas comosus) wastes is a pressing environmental issue due to pollution risks when accumulated in large quantities. These wastes are susceptible to microbial spoilage, posing serious environmental and health concerns. Therefore, exploring their conversion into valuable products is crucial for effective waste management. In this study, we assessed the antibiotic properties of pineapple processing wastes against prevalent fish pathogens in aquaculture. The wastes underwent various drying methods: sun-drying (SD), oven-drying (OD), and mechanical dehydration (DH). Ethanol extraction was used to isolate bioactive compounds, which were then tested for antibacterial activity at a concentration of 1000 mg/ml using the Agar Well Diffusion technique and Zone of Inhibition (ZOI) assay. Minimum Inhibitory Concentration (MIC) values were determined across six concentrations: 31.25 mg/ml, 62.50 mg/ml, 125 mg/ml, 250 mg/ml, 500 mg/ml, and 1000 mg/ml. Results indicated that all extracts from different drying processes effectively inhibited all tested aquaculture pathogens. DH extracts showed the highest antibacterial activity against Vibrio harveyi and Vibrio parahaemolyticus, with ZOI of 24.67 + 1.25 mm and 21.67 + 0.47 mm, respectively, and a consistent MIC of 250 mg/ml across all pathogens. SD extracts displayed a MIC of 125 mg/ml against Streptococcus agalactiae, while OD extracts showed a MIC of 1000 mg/ml against Edwardsiella tarda, Aeromonas veronii, and S. agalactiae, and 250 mg/ml against both Vibrio species. Comparative analysis with oxytetracycline did not reveal significant differences. These findings suggest that pineapple waste extracts have potential as natural antibacterial agents against common aquaculture pathogens, offering an eco-friendly alternative to commercial antibiotics.

An Integrated Photonic Biosensing Platform for Pathogen Detection in Aquaculture.

Aquaculture is expected to play a vital role in solving the challenge of sustainably providing the growing world population with healthy and nutritious food. Pathogen outbreaks are a major risk for the sector, so early detection and a timely response are crucial. This can be enabled by monitoring the pathogen levels in aquaculture facilities. This paper describes a photonic biosensing platform based on silicon nitride waveguide technology with integrated active components, which could be used for such applications. Compared to the state of the art, the current system presents improvements in terms of miniaturization of the Photonic Integrated Circuit (PIC) and the development of wafer-level processes for hybrid integration of active components and for material-selective chemical and biological surface modification. Furthermore, scalable processes for integrating the PIC in a microfluidic cartridge were developed, as well as a prototype desktop readout instrument. Three bacterial aquaculture pathogens (Aeromonas salmonicida, Vagococcus salmoninarum, and Yersinia ruckeri) were selected for assay development. DNA biomarkers were identified, corresponding primer-probe sets designed, and qPCR assays developed. The biomarker for Aeromonas was also detected using the hybrid PIC platform. This is the first successful demonstration of biosensing on the hybrid PIC platform.

Antagonistic Effects and the Underlying Mechanisms of Bacillus velezensis and its Antibacterial Peptide LCI Against Aeromonas hydrophila Infection in Largemouth Bass.

Aeromonas hydrophila is one of the most prevalent pathogenic bacteria in largemouth bass. The use of antibiotics to inhibit A. hydrophila poses a significant threat to fish and environmental safety. Bacillus velezensis, a safe bacterium with probiotic and antibacterial characteristics, is an ideal candidate for antagonizing A. hydrophila. This study explored the antagonistic effects of B. velezensis FLU-1 on A. hydrophila in vivo and in vitro. In addition, we explored the antimicrobial peptides (AMPs) produced by strain FLU-1 and clarified the underlying antibacterial mechanisms. The results showed that strain FLU-1 could inhibit a variety of fish pathogens, including A. hydrophila. The challenge test showed that dietary supplementation with B. velezensis FLU-1 significantly improved the survival rate of largemouth bass and reduced the bacterial load in liver. Subsequently, the AMP LCI was isolated from B. velezensis FLU-1 and was found to be effective against A. hydrophila in vitro and in vivo. Transcriptomic analysis revealed that LCI downregulated the genes associated with flagellar assembly and peptidoglycan synthesis in A. hydrophila. Phenotypic test results showed that LCI disrupted the membrane integrity, markedly reduced the biofilm biomass and diminished the swimming motility of A. hydrophila. Furthermore, the results showed that LCI bound to the genomic DNA of A. hydrophila and destroyed the DNA structures. Overall, these findings elucidated the mechanism of action of LCI against A. hydrophila at the phenotypic and physiological levels. This study suggests that B. velezensis FLU-1 and its AMP LCI could serve as antibiotic alternatives for controlling pathogens in aquaculture.

Seaweed assisted preparation of Fe2O3 nanoparticles and their antiviral studies against White Spot Syndrome Virus (WSSV): In vitro and in silico approach.

In the present study, preparation of Fe2O3 nanoparticles using seaweed Sargassum swartzii extract and characterized using XRD, FTIR, and FE-SEM with EDAX analysis. The crystalline nature of γ-Fe2O3 nanoparticles (hematite powders) were confirmed using XRD. In FT-IR spectra of the Fe2O3 nanoparticles, the major bands at 594 cm−1 and 461 cm−1 observed correspond to the metal‑oxygen (FeO) vibrational modes. The surface morphology of Fe2O3 nanoparticles has been studied by FE-SEM. In vitro toxicity and anti-WSSV activity of Fe2O3 nanoparticles were carried out using the shrimp-insect hybrid cell line (PmLyo-Sf9). The bioactivity of Fe2O3 nanoparticles against the WSSV infected with the PmLyo-SF9 cell line was analyzed through dose-dependent attachment inhibition and virucidal activity at an optimum concentration of 320 μg/mL and confirmed by the expression of viral envelope protein VP28. Further, the computational approach of VP28 envelope protein and Fe2O3 binding affinity was confirmed using molecular docking studies. Hence, the Fe2O3 nanoparticles can be formulated as an anti-viral agent against the aquaculture pathogens in efficient disease control.

Ocimum sanctum as a Source of Quorum Sensing Inhibitors to Combat Antibiotic Resistance of Human and Aquaculture Pathogens.

Biofilms play a decisive role in the infectious process and the development of antibiotic resistance. The establishment of bacterial biofilms is regulated by a signal-mediated cell-cell communication process called "quorum sensing" (QS). The identification of quorum sensing inhibitors (QSI) to mitigate the QS process may facilitate the development of novel treatment strategies for biofilm-based infections. In this study, the traditional medicinal plant Ocimum sanctum was screened for QS inhibitory potential. Sub-MICs of the extract significantly affected the secretion of EPS in Gram-negative human pathogens such as Escherichia coli, Pseudomonas aeruginosa PAO1, Proteus mirabilis, and Serratia marcescens, as well as aquaculture pathogens Vibrio harveyi, V. parahaemolyticus, and V. vulnificus, which render the bacteria more sensitive, leading to a loss of bacterial biomass from the substratum. The observed inhibitory activity of the O. sanctum extract might be attributed to the presence of eugenol, as evidenced through ultraviolet (UV)-visible, gas chromatography-mass spectroscopy (GC-MS), Fourier transformer infrared (FTIR) spectroscopy analyses, and computational studies. Additionally, the QSI potential of eugenol was corroborated through in vitro studies using the marker strain Chromobacterium violaceum.

Antibacterial, anticancer and antioxidant effects of sulfated galactan from Halymenia dilatata: In vitro and in vivo analysis

Seaweed has raised great interest as an excellent source of bioactive components, including vitamins, minerals, polysaccharides, polyphenols, and unique secondary metabolites which reveal broad-spectrum biological activities. In particular, the complex polysaccharides from brown, red and green seaweed possess numerous therapeutic properties. The galactan is routinely used in biomedical research. This study investigates the bioactive properties of sulfated galactan (Hd-SG) derived from the red macroalgae Halymenia dilatata, including its anticancer, antibacterial, anti-biofilm and antioxidant activity. The isolated Hd-SG exhibited potent cytotoxicity against MDA-MB-231 cells with a half-maximum inhibitory concentration (IC50) of 75 μg/ml. It was found that Hd-SG had antibacterial activity against Vibrio alginolyticus, a coastal aquaculture pathogen, with a minimum inhibitory concentration of 300 μg/ml. Toxicology analysis revealed that the isolated Hd-SG was not toxic to zebrafish embryos, even at higher concentrations (100 μg/ml). Moreover, zebrafish embryos treated with Hd-SG at a concentration of 100 μg/ml exhibited a 118.8% reduction in oxidative damage caused by H2O2-induced reactive oxygen species (ROS) production compared to the H2O2 alone treated embryos (562%). In summary, this study demonstrated that the sulfated galactan of H. dilatata has a wide range of therapeutic properties, making it a viable option for biomedical and aquaculture preventive medicine.

Vibrio pathogens and their toxins in aquaculture: A comprehensive review

AbstractAquaculture is an indispensable food source for the growing world population. In the last decades, its intensification has increased the incidence of viral and bacterial infections, emphasizing the need for novel disease management strategies. Vibrionaceae bacteria are widespread in aquatic environments, affecting various host species, including economically important fish, shrimp and bivalves. Also, human consumption of undercooked aquatic food contaminated with Vibrionaceae and/or their toxins poses a threat to human health, leading to conditions such as gastroenteritis, wound infection and sepsis. In addition, small fish and shrimp, in open aquaculture systems, can be eaten by birds that can then carry and spread this pathogen to livestock and humans. Many Vibrionaceae produce toxins, some detrimental or even lethal to the hosts, others affecting surrounding bacteria. This review provides a comprehensive overview of Vibrio toxins affecting aquatic (in)vertebrate, summarizing findings on molecular structures, mechanisms of action and regulation and secretion processes involved. Important toxin classes for microbe–host interactions, such as haemolytic, proteolytic and MARTX toxins, are discussed, along with other toxins like PirAB produced by the AHPND‐causing Vibrio parahaemolyticus. The review also emphasizes the importance of microbe–microbe interactions, particularly the production of bacteriocins by Vibrio species (Vibriocins) and antibacterial effectors produced by the Type 6 Secretion System (T6SS). While whole genome sequencing has identified putative virulence factors that are toxins, many toxins remain partially characterized or uncharacterized. Elucidating their regulation, secretion and molecular characteristics can provide valuable information and lead to novel solutions for managing Vibrio pathogens in aquaculture.

Synergies of co-infecting pathogens, sea lice (Lepeophetheirus salmonis) and Moritella viscosa, are impacted by exposure order, and host response to initial infection

Sea lice infestations and winter ulcer disease caused by Moritella viscosa are two major challenges for the Atlantic salmon (Salmo salar) aquaculture industry. Despite their common tropisms for the skin/muscle, we know very little about the interaction between these two significant pathogens. The objective of this study was to elucidate the transcriptomic response of Atlantic salmon to sea louse (Lepeophtheirus salmonis) and M. viscosa under single infection and different scenarios of co-infection (i.e., first, L. salmonis and then, M. viscosa and vice versa). After exposure, sampling was performed from the infestation site as well as the adjacent area on fish skin, followed by transcriptome analysis. RNA-seq analysis revealed that infection with either L.salmonis or M. viscosa induced a significant immune response from the skin and resulted in extensive transcriptomic changes. More differentially expressed genes (DEGs) were detected at M. viscosa lesion sites compared to L. salmonis attachment sites. In addition, the effect of the infection order was evaluated. Interestingly, we found that primary infection with lice was associated with a significantly higher number of DEGs during the co-infection process on fish skin compared to the fish first infected with M. viscosa (721 and 5336 DEGs from lice attachment and M. viscosa lesion sites, respectively, vs 291 and 3601 DEGs from lice attachment and M. viscosa lesion sites, respectively). We also found that lice infection caused localized effects on the skin of Atlantic salmon, while single infection with M. viscosa caused a moderate systemic impact and inhibited the tissue repair function of the skin, leading to severe ulceration. In addition, the C-type lectin receptor signaling pathway was drastically activated at the lice attachment sites during both lice alone- and co-infections, regardless of the order of infections, and similar results were observed in M. viscosa infection at both lesion and adjacent sites, indicating that this pathway played an essential role for immunity in Atlantic salmon. A more intense inflammatory and immune response was also observed at M. viscosa lesion sites. These results will promote our understanding of the immune interactions between L. salmonis and M. viscosa during the co-infection process and provide insights for the development of preventive and treatment strategies for these pathogens in salmonid aquaculture.

An ex vivo Approach in European Seabass Leucocytes Supports the in vitro Regulation by Postbiotics of Aip56 Gene Expression of Photobacterium damselae subsp. piscicida.

Shewanella putrefaciens Pdp11 (SpPdp11) is a probiotic strain assayed in aquaculture; however, its postbiotic potential is unknown. Postbiotics are bacterial metabolites, including extracellular products (ECPs) that improve host physiology and immunity. Their production and composition can be affected by different factors such as the growing conditions of the probiotics. Photobacterium damselae subsp. piscicida strain Lg 41/01 (Phdp) is one of the most important pathogens in marine aquaculture. The major virulent factor of this bacterium is the exotoxin aip56, responsible for inducing apoptosis of fish leucocytes. Viable SpPdp11 cells have been reported to increase resistance to challenges with Phdp. This work aimed to evaluate the effect of two ECPs, T2348-ECP and FM1548-ECP, obtained from SpPdp11 grown under different culture conditions that previously demonstrated to exert different degradative and non-cytotoxic activities, as well as the effect on pathogens biofilm formation. These SpPdp11-ECPs were then analyzed by their effect on the viability, phagocytosis, respiratory burst and apoptogenic activity against European sea bass leucocytes infected or not with Phdp supernatant. Both ECPs, T2348-ECP and FM1548-ECP, were not cytotoxic against leucocytes and significantly reduced their apoptosis. Phagocytosis and respiratory burst of leucocytes were significantly reduced by incubation with Phdp supernatant, and not influenced by incubation with T2348-ECP or FM1548-ECP. However, both activities were significantly increased after leucocyte incubation with combined T2348-ECP and FM1548-ECP with Phdp supernatant, compared to those incubated only with Phdp supernatant. Finally, both T2348-ECP and FM1548-ECP significantly reduced the relative in vitro expression of the Phdp aip56 encoding gene.

Antibacterial insights into alternariol and its derivative alternariol monomethyl ether produced by a marine fungus.

Alternaria alternata FB1 is a marine fungus identified as a candidate for plastic degradation in our previous study. This fungus has been recently shown to produce secondary metabolites with significant antimicrobial activity against various pathogens, including methicillin-resistant Staphylococcus aureus (MRSA) and the notorious aquaculture pathogen Vibrio anguillarum. The antibacterial compounds were purified and identified as alternariol (AOH) and its derivative, alternariol monomethyl ether (AME). We found that AOH and AME primarily inhibited pathogenic bacteria (MRSA or V. anguillarum) by disordering cell division and some other key physiological and biochemical processes. We further demonstrated that AOH could effectively inhibit the unwinding activity of MRSA topoisomerases, which are closely related to cell division and are the potential action target of AOH. The antibacterial activities of AOH and AME were verified by using zebrafish as the in vivo model. Notably, AOH and AME did not significantly affect the viability of normal human liver cells at concentrations that effectively inhibited MRSA or V. anguillarum. Finally, we developed the genetic operation system of A. alternata FB1 and blocked the biosynthesis of AME by knocking out omtI (encoding an O-methyl transferase), which facilitated A. alternata FB1 to only produce AOH. The development of this system in the marine fungus will accelerate the discovery of novel natural products and further bioactivity study.IMPORTANCEMore and more scientific reports indicate that alternariol (AOH) and its derivative alternariol monomethyl ether (AME) exhibit antibacterial activities. However, limited exploration of their detailed antibacterial mechanisms has been performed. In the present study, the antibacterial mechanisms of AOH and AME produced by the marine fungus Alternaria alternata FB1 were disclosed in vitro and in vivo. Given their low toxicity on the normal human liver cell line under the concentrations exhibiting significant antibacterial activity against different pathogens, AOH and AME are proposed to be good candidates for developing promising antibiotics against methicillin-resistant Staphylococcus aureus and Vibrio anguillarum. We also succeeded in blocking the biosynthesis of AME, which facilitated us to easily obtain pure AOH. Moreover, based on our previous results, A. alternata FB1 was shown to enable polyethylene degradation.

Antibacterial activity of a short de novo designed peptide against fish bacterial pathogens

In the face of increasing antimicrobial resistance in aquaculture, researchers are exploring novel substitutes to customary antibiotics. One potential solution is the use of antimicrobial peptides (AMPs). We aimed to design and evaluate a novel, short, and compositionally simple AMP with potent activity against various bacterial pathogens in aquaculture. The resulting peptide, KK12YW, has an amphipathic nature and net charge of + 7. Molecular docking experiments disclosed that KK12YW has a strong affinity for aerolysin, a virulence protein produced by the bacterial pathogen Aeromonas sobria. KK12YW was synthesized using Fmoc chemistry and tested against a range of bacterial pathogens, including A. sobria, A. salmonicida, A. hydrophila, Edwardsiella tarda, Vibrio parahaemolyticus, Pseudomonas aeruginosa, Escherichia coli, Staphylococcus epidermidis, and methicillin-resistant S. aureus. The AMP showed promising antibacterial activity, with MIC and MBC values ranging from 0.89 to 917.1 µgmL−1 and 3.67 to 1100.52 µgmL−1, respectively. In addition, KK12YW exhibited resistance to high temperatures and remained effective even in the presence of serum and salt, indicating its stability. The peptide also demonstrated minimal hemolysis toward fish RBCs, even at higher concentrations. Taken together, these findings indicate that KK12YW could be a highly promising and viable substitute for conventional antibiotics to combat microbial infections in aquaculture.

Integrating BaFe2O4 nanoparticles onto N-doped Bi2WO6 microspheres for eminent visible light-driven photocatalytic performance towards aquaculture contaminants and pathogens

Constructing highly effective visible light-responsive photocatalysts with robust redox capability is of great significance for remediation of environmental contaminants. Herein, a novel Z-scheme 0D/3D BFO/NBWO composite was successfully fabricated via a facile precipitation-hydrothermal approach. The physicochemical and optoelectronic properties of the obtained photocatalysts were affirmed via different characterization techniques. Under visible light irradiation, the 2-BFO/NBWO composite demonstrated the top-flight photocatalytic degradation of tetracycline (TC), which was 10.6, 6.0, 4.2 and 4.6-fold greater than those of BFO, BWO, NBWO and 2-BFO + NBWO, respectively. Such photocatalytic enhancement was primarily attributed to the acceleration of charge separation and migration in Z-scheme heterojunction. Additionally, the 2-BFO/NBWO composite displayed good versatility to pH variation in the solution, resistance to coexisting anions and humic acid as well as satisfactory reusability after five-cycle experiments. More importantly, real aquaculture effluent-containing TC, bisphenol A (BPA), malachite green (MG) and hexavalent chromium (Cr(VI)) were also successfully treated. The toxicity findings also proved that the treated aquaculture effluent appeared to have no significant noxious effect on Danio rerio after 2-BFO/NBWO photocatalysis. In addition to the examination of organic contaminants degradation, the prepared 2-BFO/NBWO composite was also effectively used to eradicate Escherichia coli (E. coli) and Bacillus cereus (B. cereus). The hydroxyl radicals were found to make predominant contributions to the photocatalytic reactions. This work gives a new avenue for fabricating Z-scheme composite photocatalysts with effective interfacial charge migration to degrade various organics and to eradicate pathogens from effluents.