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Abstract This study investigates the impact of environmental factors on the quality changes of mackerel (Scomber japonicus), a globally significant fish species valued for its high nutritional content, especially its unsaturated fatty acids and proteins. In South Korea, marine products like mackerel undergo auction, sorting, packaging, and transportation. Assessing the fish freshness and quality during these processes, before it reaches consumers, is crucial. This research aimed to track the changes in mackerel quality indicators after the auction and correlate them with the environmental factors affecting transportation. Using a transportation model established for both summer and winter, mackerel samples were categorized by their weight (200 and 300 g). Results show poorer quality indicators in summer compared to winter, particularly in the 200 g group. Microbiological indicators such as the total viable count (0.923) and total coliforms (0.958) were most strongly correlated with the season, whereas the lipid oxidation indicators acid value (0.627) and peroxide value (0.536) were moderately correlated with the season. Interestingly, the wider standard deviation distribution observed in summer suggests that individual mackerel characteristics may influence the degree of quality changes. These findings offer insights into mackerel quality fluctuations during auction and transportation, aiding in future efforts to maintain seafood quality amidst climate change.

The strategy of cultivating healthy fish by manipulating their gut microbiota composition using probiotics is crucial for establishing sustainable fish farms. Information on the gut microbiota composition of healthy fish is important for the efficient development of probiotics and the aquaculture strategies that would apply them. This study assessed the gut microbiota composition of farmed olive flounder according to the growth stage to provide useful information for the development of probiotics. The fish were classified according to their weight, and the intestines of five juveniles weighing less than 100 g and five subadults weighing between 400 and 800 g were used for analysis. The results of alpha diversity analysis confirmed higher richness and diversity in the subadult group than in the juvenile group. Beta diversity analysis revealed clear boundaries and distances between the groups; however, individuals within each group were similar. The two groups showed marked differences in their gut microbiota composition. Phylum-level analysis revealed that the most abundant phylum was Proteobacteria in the juvenile group and Firmicutes in the subadult group. Notably, genus-level analysis revealed that Vibrio accounted for more than 50% of the total composition in the juvenile group. Linear discriminant analysis effect size revealed that the genera Vibrio, Photobacterium, and Leuconostoc were representative of the juvenile group, whereas 19 genera, including Lactococcus and Vagococcus, were representative of the subadult group. Thus, information on the representative microorganisms abundantly present in the intestines of healthy olive flounder can be considered for the selection and development of a probiotic genus for olive flounder farming.

Beta-glucan (β-glucan), a naturally occurring complex polysaccharide, has drawn attention for its diverse health benefits, including immune system modulation. β-glucan was extracted from two fungi, Monascus purpureus (Mp) and Monascus kaoliang (Mk), cultured in Saccharina japonica via submerged fermentation. The yield, solubility, total sugar, reducing sugar, protein content, Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Thermogravimetric analysis (TGA), Scanning Electron Microscopy (SEM), in vitro free radical scavenging activity, and cytotoxicity were analyzed. A significant yield of β-glucans, with the contents of 51.30 ± 1.54% in Mp and 44.24 ± 1.18% in Mk was observed on a dry weight basis. Water solubility slightly varied, measuring 36.25 ± 1.14% in Mp and 31.25 ± 0.94% in Mk. Total sugar and reducing sugar content in Mp and Mk derived β-glucans were 114.75 ± 2.54 mg/g and 100.25 ± 1.86 mg/g, 7.38 ± 0.78 mg/g, and 8.39 ± 0.46 mg/g, respectively. FTIR spectra resembled the standard, and TGA confirmed heat stability. XRD patterns indicated that the extracted β-glucans, including the standard one, showed the most prominent diffraction peaks in the lower 2θ range, suggesting similar crystalline phases; however, they differed in crystallinity and degree of amorphous content. SEM images displayed characteristic rough and fibrous shapes and surfaces for extracted β-glucans but it was uniform and of a regular shape in the standard sample. The isolated β-glucans exhibited in vitro free radical scavenging and no cytotoxicity was observed in the MTS assay. Therefore, utilizing S. japonica as a substrate in the fermentation process by Monascus spp. presents a unique opportunity in the production and utilization of β-glucans.

The present study constitutes the first attempt to identify low-temperature intestinal probiotics for olive flounder (Paralichthys olivaceus) and analyze their effects on this species at 20 °C, which is its optimum culture temperature. Initially, 291 intestinal bacteria were isolated, and Rummeliibacillus stabekisii PM227 (PM227), Microbacterium oxydans NB29 (NB29), and Microbacterium foliorum BZ24 (BZ24), which successfully passed the characterization tests, were considered for dietary supplementation. The formulated diets, denoted as Pro1, Pro2, and Pro3, contained 1 × 108 CFU/g of PM227, NB29, and BZ24, respectively, whereas the control diet contained no probiotics. Triplicates of 20 fish (10.34 ± 0.26 g) were randomly allocated to the four diet groups and fed one of the diets for 8 weeks. At the end of the trial, Pro2 and Pro3 significantly increased growth and feed utilization parameters compared to the control and Pro1 groups. Only Pro2 and Pro1 improved (p < 0.05) myeloperoxidase activity and the transcription of interleukin (IL)-10 in the fish liver, respectively. Amylase, lipase, and protease activities were increased in the flounder intestine in all three potential probiotics groups, except for amylase in Pro2. Intestinal microbial richness (Chao1 index) and diversity (Shannon index) were higher in Pro2 than in the other diet groups, with some similarities observed between Pro1 and Pro3. A significantly lower relative abundance of Firmicutes and Staphylococcales was found in the intestine of all probiotics-supplemented flounder. Moreover, the relative abundance of Lactobacillus and Staphylococcus exhibited the following order among the examined groups: Pro1 > Pro3 > Pro2 > control and control > Pro2 > Pro1 > Pro3, respectively. Therefore, the identified low-temperature potential probiotics increased growth, immunity, digestive enzyme activities, and intestinal microbial populations in olive flounder, demonstrating their value as feed supplements in the flounder industry.

Abstract This study investigated the effects of supplementation of low-temperature probiotics isolated from the intestines of olive flounder on the growth performance, digestibility, and regulation of intestinal microbiota and the expression of genes related to growth, immunity, and apoptosis in olive flounder. Bacteria showing high growth at approximately 15–20 °C, which is the temperature of olive flounder culture, were isolated and confirmed to be Pseudomonas species through 16S rRNA gene sequence analysis. Whole-genome sequencing revealed that the strain has a 6,195,122 bp single circular chromosome and a guanine–cytosine content of 59.9%. In the feeding trial, supplementation with 1 × 108 CFU/g of the isolate strain positively modulated growth performances, digestive enzyme activity, and gut microbiota composition of olive flounder. RT-qPCR for the comparison of growth, immunity, and apoptosis-related gene expression levels showed no significant differences between the groups. Therefore, the isolated host-associated low-temperature probiotics improved the growth performance of olive flounder by causing positive changes in digestive activity and intestinal microbial composition without affecting host gene expression.

Host-associated probiotics (HAPs) are bacteria originally isolated from rearing water or the host's gastrointestinal tract in order to enhance the host's growth and health. This study investigated the HAP potential of Bacillus sp. PM8313, isolated from wild red sea bream (Pagrus major), through characterization and feeding trials. Results based on in vitro tests showed that PM8313 is safe, confirming its hemolytic, cytotoxic, and antibiotic resistance. In addition, PM8313 showed advantages as a probiotic with high viability in the gastrointestinal model and a high cell adhesion rate. Whole-genome sequencing demonstrated that PM8313 has a 4,615,871 bp single circular chromosome and a guanine–cytosine content of 45.25%. It also showed the absence of genes encoding virulence factors, such as cytotoxin, enterotoxin, hemolysin, sphingomyelinase, and phospholipase. In the feeding trial, a supplemental diet of 1 × 108 CFU/g PM8313 positively altered the weight gain, digestive enzyme activity, and intestinal microbiota composition of red sea bream. Analysis of nonspecific immune parameters and immune-related gene expression, and a challenge test showed that PM8313 supplementation increases immunity and pathogenic bacteria resistance. Our findings suggest that PM8313 should be considered for application as a novel HAP to red sea bream aquaculture.

Two novel strains of Rummeliibacillus sp. and Microbacterium sp. were identified from the intestine of olive flounder (Paralichthys olivaceus) and characterized in vitro as potential probiotics. Feeds without probiotic and with a 50:50 mixture of these two strains (1 × 108 CFU/g feed) were denoted as the control and Pro diets, respectively. Three randomly selected tanks (20 flounders/tank, ~11.4 g each) were used for each diet replication. After 8 weeks of feeding, the growth and feed utilization of the flounder in the Pro group improved (p < 0.05) compared to the control. Among four immune parameters, only myeloperoxidase activity was elevated in the Pro group. Serum biochemistry, intestinal microbial richness (Chao1), and diversity (Shannon index) remained unchanged (p ≥ 0.05), but phylogenetic diversity was enriched in the Pro fish intestine. Significantly lower Firmicutes and higher Proteobacteria were found in the Pro diet; the genus abundance in the control and Pro was as follows: Staphylococcus > Lactobacillus > Corynebacterium and Lactobacillus > Staphylococcus > Corynebacterium, respectively. Microbial linear discriminant scores and a cladogram analysis showed significant modulation. Therefore, the combination of two host-associated probiotics improved the growth and intestinal microbial population of flounder and could be supplemented in the Korean flounder industry.

A 6-month feeding trial was conducted to compare the effects of extruded pellet (EP) and moist pellet (MP) feed on the growth performance, non-specific immunity, and intestinal microbiota of olive flounder. A total of 60,000 fish with an average weight of 70.8 ± 6.4 g were divided into two groups and fed with one of two experimental diets. At the end of a 6-month feeding trial, the weight gain and specific growth rate of the fish fed with the MP diets were significantly higher than those of fish fed with EP (P < 0.05). However, the EP group exhibited a lower feed conversion rate than the MP group, meaning that the EP diet was more cost-effective. Whole-body proximate compositions and non-specific immune responses (superoxide dismutase, myeloperoxidase, and lysozyme activity) were not significantly different between the two groups. There were no significant differences in the α-diversity of the intestinal bacterial community of the two groups. However, the composition of microorganisms at the phylum to genus level was different between the groups. The EP group was rich in Actinobacteria, Corynebacterium, Bacillus, and Lactobacillus, whereas the MP group was dominated by Proteobacteria, Vibrio, and Edwardsiella. Collectively, the MP diet increased growth performance and pathogen concentration in the gut; whereas EP improved feed conversion and beneficial Bacillus and Lactobacillus proportion in the intestinal microbial community.

The fish gut microbiota plays an important role in overall health. However, few reports have described the changes in the composition of gut microbiota following infection with pathogenic bacteria in olive flounder (Paralichthys olivaceus). Here, we reported the changes in the gut microbiota composition of flounder after treatment with each of the three pathogenic bacteria (Edwardsiella tarda, Streptococcus iniae, and Vibrio harveyi). Edwardsiella tarda infection decreased the relative abundance of Verrucomicrobia and increased Proteobacteria abundance at the phylum level of the gut microbiota over time. Similarly, Streptococcus iniae infection reduced the relative abundance of Verrucomicrobia. Vibrio harveyi infection caused a decrease in the relative abundance of Firmicutes and Verrucomicrobia and increased Proteobacteria. At the genus level, infection with all three pathogens increased the relative abundance of Ralstonia and Sphingomonas species. Conversely, this infection decreased the relative abundances of Rubritalea, Saccharimonas, and Bacillus species. Therefore, reducing the abundance of Ralstonia and Sphingomonas and increasing the abundance of Rubritalea, Saccharimonas, and Bacillus in the gut microbiota composition of flounder might help maintain a healthy gut microbiota balance. This research might be useful for future studies on improving the health of flounder through gut microbiota regulation.

Intensification of aquaculture has led to frequent occurrence of disease outbreaks. To deal with this issue antibiotics are a widely-preferred control strategy, but one that poses risks to the environment and humans, if used indiscriminately. In pursuit of an alternative, probiotics have emerged recently among viable alternatives for health management in aquaculture. The prophylactic use of probiotics in farmed shellfish species, i.e., shrimp, prawn, crab, crayfish, oyster and abalone, has been demonstrated to enhance production, promote the host internal microbiota, resulting in reduced incidence of bacterial, parasitic and even viral (e.g., White Spot Syndrome Virus/WSSV, Yellowhead disease/YHD) diseases. Probiotics can be administered either as feed supplements or directly into rearing water, the former being generally more effective. Although precise modes of action are unknown, probiotics can deliver some measure of sustainability to shellfish aquaculture in multiple ways, including contributions to pathogen exclusion, better growth, survival and feed utilization, and immune modulation. Antiviral mechanisms of probiotics are not well documented, but certain protobionts such as Bacillus and Lactobacillus have been effective in developing disease resistance and in reducing the prevalence of WSSV and YHD in a number of studies. This review discusses recent advances on the role of probiotics in shellfish aquaculture, emphasizing their prophylactic activity against viral diseases.

A 56-day feeding trial was conducted to determine the effect of dietary supplementation with Bacillus sp. isolated from the intestines of red sea bream on the growth performance, immunity, and gut microbiome composition of red sea bream. Three diets (a control diet and two treatments) were formulated without Bacillus sp. PM8313 or β-glucan (control, CD), 1 × 108 CFU g−1 PM8313 (BSD), and 1 × 108 CFU g−1 PM8313 + 0.1% β-glucan (BGSD). At the end of the experiment, the weight, specific growth rate, feed conversion ratio, and protein efficiency ratio of the fish in the BSD and BGSD diet groups were significantly improved than those of the control group (P < 0.05). Additionally, amylase and trypsin activities were significantly higher (P < 0.05) in both groups compared to the control. Superoxide dismutase and lysozyme activity, which are serum non-specific immune responses, only increased in the BGSD group. The two treatment groups exhibited a marked difference in the intestinal microbiota composition compared to the control group. Furthermore, the treatment groups exhibited an upregulation of IL-6 and NF-κb, coupled with high survival rates when challenged with Edwardsiella tarda. Therefore, dietary supplementation with PM8313 improved the growth performance, digestive enzyme activity, non-specific immunity, and pathogen resistance of red sea bream, in addition to affecting the composition of its intestinal microflora.

This study was performed to investigate the effect of microbial supplementation diet on the survival rate and microbiota composition of artificially produced eel larvae. Microorganisms supplemented in the diet were isolated from wild glass eel intestines and identified as Bacillus sp. through 16S rRNA sequencing analysis. In vitro tests confirmed that the strain had no hemolytic activity and virulence genes. Microbial supplemental feeding significantly increased the survival rate of artificially produced eel larvae for 30 days post-hatchling compared with that of the control group. It also caused changes in the α-diversity, β-diversity, and relative abundance of the bacterial communities. Analysis via phylogenetic investigation of communities by reconstruction of unobserved states predicted that these microbial community changes would significantly increase the carbohydrate metabolism, membrane transport, and cellular community pathway of the microbial supplementation group. Therefore, microbial supplementation feeding for eel aquaculture could increase the viability of artificially produced eel larvae and alter the microbial composition to induce metabolic changes.

Beneficial microorganisms can increase nutrient digestion and absorption in farmed fish. This study investigates the effects of supplemental feeding of Bacillus species isolated from the intestines of wild glass eels on the growth, survival, and gene expression of farm-raised eel larvae for 30 days after hatching. Three species of Bacillus (B. velezensis, AJBV; B. subtilis, AJBS; B. licheniformis, AJBL) without hemolytic activity were isolated, and an experiment compared the growth of eel larvae fed an artificial diet supplemented with each Bacillus species. There were no significant differences in the total length and body depth of eel larvae at 30 days after hatching in all groups. During the feeding period, 149 eels survived from the initial 1000 in the control group. On the other hand, 240, 178, and 141 eels survived in the AJBV, AJBS, and AJBL groups, respectively. However, there were no significant differences in survival rates despite the difference in the number of surviving eel larvae among the groups. In the comparison of gene expression of genes involved with growth (growth hormone, growth hormone receptor 1, insulin-like growth factor II-2) and those involved with digestive enzymes (amylase, trypsin, lipase), there were also no significant differences among the groups. Our results confirm that dietary supplementation with each of the three host-associated Bacillus does not affect the growth and survival rates of eel larvae reared on an artificial diet up to the first 30 days after hatching, nor does it significantly affect related gene expression.

In the present study, the probiotic properties of Pediococcus acidilactici FS2 isolated from Korean traditional food, gajami-sikhae (fermented flounder), and the effect of its oral administration on the reduction in blood cholesterol in mice were investigated. Analysis of probiotics properties, such as acid and bile resistance, antibiotic resistance, cell adhesion, antioxidant activity, antibacterial activity, and enzyme activity, demonstrated that FS2 is a potential probiotic candidate. FS2 showed a high growth rate when isomalto-oligosaccharides (IMO) were used as a prebiotic. Moreover, an oral administration of the combination of FS2 and IMO to the mice for 5 weeks increased the number of intestinal lactic acid bacteria and decreased the levels of serum total triglyceride, cholesterol, and low-density lipoprotein cholesterol. Therefore, the findings of the present study suggest that FS2 is functional and safe as a probiotic and can reduce blood cholesterol levels when taken along with IMO.

Monascus-fermented Saccharina japonica extract was evaluated to prevent preadipocyte to adipogenic differentiation in 3T3L-1 cells. The Oil red O staining of sample treated 3T3L-1 cells showed reduction of lipid accumulation and adipocyte differentiation in a dose dependent manner. The mRNA gene expression measured by real-time polymerase chain reaction (Q-PCR) for adipogenic gene expression showed that the C/EBP-α expression was significantly (p

A new strain of coronavirus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) responsible for the coronavirus disease 2019 (COVID-19) pandemic was first detected in the city of Wuhan in Hubei province, China in late December 2019. To date, more than 1 million deaths and nearly 57 million confirmed cases have been recorded across 220 countries due to COVID-19, which is the greatest threat to global public health in our time. Although SARS-CoV-2 is genetically similar to other coronaviruses, i.e., SARS and Middle East respiratory syndrome coronavirus (MERS-CoV), no confirmed therapeutics are yet available against COVID-19, and governments, scientists, and pharmaceutical companies worldwide are working together in search for effective drugs and vaccines. Repurposing of relevant therapies, developing vaccines, and using bioinformatics to identify potential drug targets are strongly in focus to combat COVID-19. This review deals with the pathogenesis of COVID-19 and its clinical symptoms in humans including the most recent updates on candidate drugs and vaccines. Potential drugs (remdesivir, hydroxychloroquine, azithromycin, dexamethasone) and vaccines [mRNA-1273; measles, mumps and rubella (MMR), bacille Calmette-Guérin (BCG)] in human clinical trials are discussed with their composition, dosage, mode of action, and possible release dates according to the trial register of US National Library of Medicines (clinicaltrials.gov), European Union (clinicaltrialsregister.eu), and Chinese Clinical Trial Registry (chictr.org.cn) website. Moreover, recent reports on in silico approaches like molecular docking, molecular dynamics simulations, network-based identification, and homology modeling are included, toward repurposing strategies for the use of already approved drugs against newly emerged pathogens. Limitations of effectiveness, side effects, and safety issues of each approach are also highlighted. This review should be useful for the researchers working to find out an effective strategy for defeating SARS-CoV-2.

An eight-week feeding trial was conducted to evaluate the effects of different dietary probiotic supplements in juvenile whiteleg shrimp, Litopenaeus vannamei. A basal control diet without probiotics (CON), and five other diets by supplementing Bacillus subtilis at 107 CFU/g diet (BS7), B. subtilis (BS8), Pediococcus pentosaceus (PP8), and Lactococcus lactis (LL8) at 108 CFU/g diet, and oxytetracycline (OTC) at 4 g/kg diet were used. Whiteleg shrimp with initial body weights of 1.41 ± 0.05 g (mean ± SD) were fed with these diets. Growth of shrimp fed BS8 and LL8 diets was significantly higher than those of shrimp fed the CON diet (p < 0.05). Superoxide dismutase activity in shrimp fed PP8 and LL8 diets was significantly higher than that of shrimp fed the CON diet (p < 0.05). Lysozyme activity of shrimp fed probiotics and OTC diets significantly improved compared to those on the CON diet (p < 0.05). The intestinal histology showed healthier guts for shrimp fed the probiotic diets (p < 0.05). Immune-related gene expression in shrimp fed BS8, PP8 and LL8 diets was recorded as significantly higher than that of shrimp fed CON and OTC diets (p < 0.05). Also, results of the challenge test for 7 days and the digestive enzyme activity of shrimp fed BS8, PP8, and LL8 were significantly improved compared to those on the CON diet (p < 0.05). Therefore, these results indicated that L. lactis at 108 CFU/g could be an ideal probiotic for whiteleg shrimp, and also B. subtilis WB60 and P. pentosaceus at 108 CFU/g could improve the growth, immunity, histology, gene expression, digestive enzyme activity, and disease resistance, while replacing antibiotics.

An eight-week feeding trial was conducted to evaluate the effects of a basal control diet (CON), Bacillus subtilis at 107 (BS7) and at 108 CFU/g diet (BS8), Lactococcus lactis at 107 CFU/g (LL7) and at 108 CFU/g diet (LL8), and oxytetracycline (OTC) at 4 g/kg diet on Nile tilapia. Fish with initial body weight of 2.83 ± 0.05 g (mean ± SD) were fed two times a day. Weight gain, specific growth rate, feed efficiency, protein efficiency ratio and lysozyme activity of fish fed BS8, LL8 and LL7 diets were significantly higher than those of fish fed CON diet (p < 0.05). Superoxide dismutase and myeloperoxidase activity of fish fed BS8, LL8, BS7, LL7 and OTC diets were significantly higher than those of fish fed CON diet. Intestinal villi length and muscular layer thickness of fish fed BS8, LL8 and LL7 diets were significantly higher than those of fish fed CON and OTC diets. Also, heat shock protein 70 (HSP70), interleukin (IL-1β), interferon-gamma (IFN-γ) and tumour necrosis factor (TNF-α) gene expression of fish fed BS8 and LL8 diets were significantly higher than those of fish fed CON diet. After 13 days of challenge test, cumulative survival rate of fish fed BS8 and LL8 diets were significantly higher than those of fish fed CON, BS7 and OTC diets. Based on these results, B. subtilis and L. lactis at 108 (CFU/g) could replace antibiotics, and have beneficial effects on growth, immunity, histology, gene expression, and disease resistance in Nile tilapia.