Paraprobiotic preparation from Bacillus amyloliquefaciens FPTB16 modulates immune response and immune relevant gene expression in Catla catla (Hamilton, 1822)

Preventive and reparative potentials of heat-inactivated and viable commensal Bacillus pumilus SE5 in ameliorating the adverse impacts of high soybean meal in grouper (Epinephelus coioides)

Probiotic Bacillus pumilus SE5, heat-inactivated (HSE5) or active (ASE5), were supplemented to high soybean meal (HSM) (36 %) diet at whole term (0-56 days) and middle term (29-56 days) to investigate the preventing and repairing effects of B. pumilus SE5 in ameliorating the adverse effects of HSM in Epinephelus coioides. The results suggested that the HSM significantly decreased the weight gain rate (WGR), specific growth rate (SGR), and increased the feed conversion rate (FCR) at day 56 (P < 0.05), while HSE5 and ASE5 promoted the growth performance. The HSE5 and ASE5 showed preventive and reparative functions on the antioxidant capacity and serum immunity, with significantly increased the total antioxidant capacity (T-AOC), superoxide dismutase (SOD), glutathione (GSH), glutathione peroxidase (GSH-PX) activities, and reduced malondialdehyde (MDA) level, and increased acid phosphatase (ACP), alkaline phosphatase (AKP), immunoglobulin M (IgM) and complement 3 (C3). The HSM impaired the intestinal health (destroyed the intestinal structure, significantly increased the contents of serum D-lactic acid and diamine oxidase, and reduced the expressions of claudin-3 and occludin), while HSE5 and ASE5 improved them at whole term and middle term. The HSM impaired the intestinal microbiota and reduced its diversity, and the HSE5 or ASE5 improved the intestinal microbiota (especially at whole term). HSE5 and ASE5 improved the intestinal mRNA expressions of anti-inflammatory genes (il-10 and tgf-β1) and reduced the expressions of pro-inflammatory genes (il-1β, il-8, il-12), and promoted the expressions of humoral immune factor-related genes (cd4, igm, mhcII-α) and antimicrobial peptide genes (β-defensin, epinecidin-1 and hepcidin-1), and decreased the expressions of NF-κB/MAPK signaling pathway-related genes (ikk-α, nf-κb, erk-1), and improved the expressions of MAPK signaling pathway-related gene p38-α (P < 0.05). In conclusion, the heat-inactivated and active B. pumilus SE5 effectively prevented and repaired the suppressive effects of soybean meal in E. coioides, which underscored the potential of B. pumilus SE5 as a nutritional intervention agent in HSM diet in aquaculture.

Harnessing paraprobiotics and postbiotics for enhanced immune function in Asian seabass (Lates calcarifer): Insights into pattern recognition receptor signaling

The Asian seabass, Lates calcarifer, is a key species in Asian aquaculture due to its nutritional value and adaptability. However, disease outbreaks, particularly viral and bacterial infections, pose significant challenges to its production. Immunostimulants offer promising solutions but raise safety concerns. Paraprobiotics and postbiotics (CPP) emerge as safer alternatives, exerting health benefits without live microorganisms. This study investigated the potential of probiotic paraprobiotic and postbiotic supplements derived from Bacillus subtilis to enhance the immune response and antioxidant capacity of Asian seabass and improve their resistance to Streptococcus iniae infection. Analysis of antioxidant activity and lipid peroxidation revealed significant improvements in fish supplemented with CPP, indicating their effectiveness in mitigating oxidative stress. Immunological assays demonstrated enhanced growth performance and serum immunity, including increased alternative complement activity, immunoglobulin levels, and phagocytic activity, in supplemented fish. Furthermore, upregulated expression of proinflammatory cytokines (TNF-α, IL-6, IL-1β) and pattern recognition receptors (NLRC3, TLR22, MDA5) in immune tissues. Fish supplemented with CPP exhibited higher resistance and survival rates against S. iniae infection challenge compared to control groups. The study elucidates the mechanisms underlying the immunomodulatory effects of CPP, shedding light on their potential applications in aquaculture.

Effect of dietary heat-killed Lactiplantibacillus plantarum VSG3 on growth, immunity, antioxidant status, and immune-related gene expression in pathogen-aggravated Cyprinus carpio

Heat-killed probiotics offer an alternative approach to enhance growth and disease resistance in farmed fish. In this study, we isolated Lactiplantibacillus plantarum VSG3 from the gut of Labeo rohita to investigate the effects of heat-killed L. plantarum (HK-LP) on the health and growth performance of Cyprinus carpio fingerlings. Different concentrations of HK-LP (0, 50, 100, 200, 300, and 400 mg/kg) were administered to the fish, followed by a challenge with Aeromonas hydrophila after 8 weeks of feeding. Notably, the LP200 group exhibited significantly improved percentage weight gain and specific growth rate, accompanied by the lowest feed conversion ratio. Post-challenge survival rates were considerably enhanced in the LP200 group, reaching 60.65%. Moreover, serum analysis indicated significantly higher levels of total protein and albumin in the LP200 group than in the control group. Although HK-LP had no substantial impact on certain serum parameters (glucose, total cholesterol, cortisol, and alanine aminotransferase), aspartate aminotransferase levels were considerably low in the LP200 group. Intestinal protease and trypsin activities significantly increased in the LP200 group, while no significant changes were observed in lipase and amylase activities post-pathogen challenge. Serum immunological indices, including lysozyme, alternative complement pathway, and phagocytic activity, improved considerably in the LP200 group. Additionally, serum antioxidant enzyme activities (superoxide dismutase [SOD], glutathione peroxidase [GPx], catalase [CAT], and myeloperoxidase) were significantly elevated in the LP200 group, while malondialdehyde level was reduced. Gene expression analysis in liver tissue indicated strong upregulation of antioxidant-related genes (SOD, CAT, nuclear factor erythroid 2 [NFE2]-related factor 2 [Nrf2], Kelch-like ECH-associated protein 1[Keap1]) in the LP100 and LP200 groups. Pro-inflammatory cytokines (IL-1β and TNF-α) were considerably downregulated in the kidneys of the LP200 post-challenged fish, although the anti-inflammatory cytokine IL-10 showed an increased expression. Quadratic regression analysis identified the optimal dietary HK-LP level for maximizing growth and immune performance (200.381-270.003 mg/kg). In summary, our findings underscore the potential of HK-LP as a valuable dietary supplement for enhancing carp aquaculture, particularly at the appropriate concentration.

Application of Bacillus Coagulans as Paraprobiotic Against Acute Hepatopancreatic Necrosis Disease in Shrimp

Paraprobiotics, known as non-viable or ghost probiotics, have attracted attention for their benefits over live microbial cells. This study was designed to investigate the paraprobiotic effects of heat-killed Bacillus coagulans on the white leg shrimp Litopenaeus vannamei. The paraprobiotic formulation was prepared in three different concentrations including B. coagulans 1 (107 cells g-1 diet), B. coagulans 2 (108 cells g-1 diet), and B. coagulans 3 (109 cells g-1 diet) through heat inactivation method. Preliminary toxicity assessments revealed that post-larvae shrimps (mean weight ± SE: 0.025 ± 0.007 g) treated with B. coagulans 1, 2 and 3 paraprobiotic formulations exhibited no mortality, confirming the non-toxic nature of the formulated diet. In a 90-day feeding trial involving juvenile shrimps (mean weight ± SE: 0.64 ± 0.05 g), growth parameters and feed conversion ratios improved in all experimental groups. Subsequently, these shrimps were challenged with Vibrio parahaemolyticus, revealing that paraprobiotic-fed shrimps exhibited significant survival rate improvements. Oxidative stress-related enzyme activities, such as superoxide dismutase and catalase, increased in paraprobiotic-fed shrimps post-Vibrio challenge, while the challenged control group showed decreased activity (p < 0.001). Nitric oxide levels are also increased in paraprobiotic-treated shrimp, with B. coagulans 3 showing a significant rise in nitric oxide activity (p < 0.001). This study further demonstrated the positive impact of paraprobiotic treatment on digestive enzymes, immune-related parameters (e.g., total hemocyte count, prophenoloxidase, and respiratory burst activity), and overall disease resistance. These findings suggest that B. coagulans paraprobiotics have the potential to enhance antioxidant, antibacterial, and immune-related responses in L. vannamei, making them a valuable addition to shrimp aquaculture.

Effects of Bacillus subtilis as a single strain probiotic on growth, disease resistance and immune response of striped catfish (Pangasius hypophthalmus)

The present study investigated the potential role of Bacillus subtilis as probiotic in striped catfish (Pangasius hypophthalmus). Fish (initial weight = 150.00±2.63g n = 180) were stocked in circular tanks. Four isonitrogenous (30%) and isolipidic (3.29%) diets were formulated having supplementation of B. subtilis at four different levels (P0; 0, P1: 1×106, P2: 1×108 and P3: 1×1010 CFU/g). Each treatment had three replicates, while each replicate had fifteen fish. The trial started on second week of July and continued for eight weeks. Growth, feed conversion ratio, crude protein content, the concentration of amylase and protease, the profile of both dispensable and non-dispensable amino acids in all four dietary groups increased with a gradual increase of B. subtilis in the diet. At the end of growth experiment, fish in all four groups were exposed to Staphylococcus aureus (5×105 CFU/ml). After S. aureus challenge, fish fed with B. subtilis responded better to damage caused by reactive oxygen species and lipid peroxidation and better survival rate. The catalase and superoxide dismutase level also increased in response to bacterial challenge in B. subtilis fed groups. On the other hand, the concentration of malondialdehyde gradually decreased in these groups (+ve P0 >P1>P2>P3). It is concluded that supplementation of B. subtilis as a probiotic improved the growth, protein content, antioxidant response and immunocompetency against S. aureus in striped catfish. The optimum dosage of B. subtilis, at a concentration of 1×1010 CFU/g, resulted in the most favorable outcomes in striped catfish. This single bacterial strain can be used as an effective probiotic in large scale production of aquafeed for striped catfish. Future studies can investigate this probiotic's impact in the intensive culture of the same species.

Effect of eco-friendly probiotics-supplemented rapeseed meal-based diet on the performance of Catla catla fingerlings

Ever-increasing human population compels the researchers to search for alternative food sources such as fish meat. For increase of fish growth and proper feed utilization, probiotics were added in rapeseed meal-based diet in current trial for proper digestion and absorption of nutrients in fish and ultimately higher growth with lower aquatic pollution. Fish gut microbiota is important for the feed utilization and absorption in body for higher growth. A 70-day study was conducted to investigate the effects of probiotics-supplemented rapeseed meal-based diet on growth performance, digestibility of nutrients, and absorption of minerals in Catla catla fingerlings with lowering water pollution level. Six test diets were prepared by using different levels of multi-strain probiotics i.e. 0, 1, 2, 3, 4 and 5 g/kg (0.0-0.5%) in rapeseed meal-based diet. At the rate of 4% of live wet weight, Catla fingerlings were fed two times a day and faeces samples from each tank were collected. According to the results, it was observed that probiotics supplementation (@2 g/kg) in rapeseed meal-based diet resulted with improvement in nutrient digestibility (CP, 72%; fat, 75% and GE, 70%), mineral absorption (Ca, 72%; Na, 76%; K, 70% and P, 70%), specific growth rate (SGR, 1.55), improved feed conversion ratio (FCR, 1.22) and weight gain percentage (WG%, 303%) of fingerlings. It was also noticed that probiotics supplementation decreased the discharge of minerals and nutrient through faeces, as compared to control diet; hence, it plays a significant role in reducing water pollution. On the basis of these results, it was concluded that probiotics inclusion at level of 2 g/kg was useful to formulate the cost effective and eco-friendly fish feed with the maximum improvement in growth and fish health by using rapeseed meal-based diet, as compared to control and other test diets.

Transcriptome analysis reveals the regulatory effects of Bacillus amyloliquefaciens and Bacillus pumilus on immune and digestive related genes in the spleen of weanling black goats

The aim of the present study was to evaluate the effects of Bacillus amyloliquefaciens fsznc-06 and Bacillus pumilus fsznc-09 on the expressions of spleen genes in weanling Jintang black goats. Bacillus amyloliquefaciens fsznc-06 (BA-treated group) and Bacillus pumilus fsznc-09 (BP-treated group) were directly fed to goats, and the spleens were harvested for transcriptome analysis. The KEGG pathway analysis showed that the differentially expressed genes (DEGs) in BA-treated vs CON group were mainly involved in digestive system and immune system, while those in BP-treated vs CON group were mainly involved in immune system, and those in BA-treated vs BP-treated group were mainly involved in digestive system. In conclusion, Bacillus amyloliquefaciens fsznc-06 might promote the expressions of genes related to immune system and digestive system, reduce the expressions of disease genes related to digestive system and might promote mutual accommodation of some immune genes in weanling black goat. Bacillus pumilus fsznc-09 might promote the expressions of genes related to immune system and mutual accommodation of some immune genes in weanling black goat. Bacillus amyloliquefaciens fsznc-06 has advantages over Bacillus pumilus fsznc-09 in promoting the expressions of genes related to digestive system and mutual accommodation of some immune genes.

The positive effects of postbiotic (SWF concentration®) supplemented diet on skin mucus, liver, gut health, the structure and function of gut microbiota of common carp (Cyprinus carpio) fed with high-fat diet

Postbiotics are an emerging research interest in recent years, which shows that metabolites, lysate extracts, cell wall components and even culture supernatants of probiotics can also exhibit significant prebiotic effects. In this study postbiotic stress worry free concentration® (SWFC) were prepared from the composition of culture supernatant of Cetobacterium somerae and Lactococcus lactis. The positive effects of SWFC supplemented diets on the growth performance, skin mucus, liver and gut health, and intestinal microbiota profile of Cyprinus carpio fed with high fat diets were investigated. 180 C. carpio with an average body weight of (3.01 ± 0.01) g were selected and randomly divided into three groups. They were fed with one of the three experimental diets supplemented with SWFC of 0 (control), 0.2 and 0.3 g/kg for 98 days, afterwards indexes were detected. The results revealed that, addition of SWFC had no significant effect on growth performance of C. carpio, while it can improve the health of the fish remarkably. In addition, SWFC improved mucosal C3, T-AOC, SOD activities, and decreased lipid peroxidation product MDA level, which were notably better than those in the control group (P < 0.05). In terms of the liver health systems, C. carpio fed on the diet supplemented with 0.2 g/kg of SWFC, showed significant improvement of the liver injured by HFD and reduce the contents of serum ALT and AST, and liver TAG (P < 0.05; P < 0.01). The expression of inflammation-related and lipid synthesis genes revealed that SWFC0.2 group could noteworthy enhance antioxidant capacity, reduced the expression of pro-inflammatory factors (TNF-α, IL-1β) and lipid synthesis genes (ACC, FAS, PPAR-β, PPAR-γ), and up-regulated the expression of anti-inflammatory factors (TGF-β). Additionally, intestinal morphology arose inflammatory cell infiltration, while intestinal integrity was better in SWFC groups compared with the control. Furthermore, the contents of serum LPS and LBP were remarkably lower in the SWFC0.2 group compared with the control (P < 0.01). The mRNA expression of genes related to gut health indicated that SWFC supplementation noteworthy up-regulated the expression of antioxidant (Nrf2, CAT, GPX), immune (Hepcidin, IL-10) and tight junction protein-related (ZO-1, Occludin). Simultaneously, the results of GF-zebrafish showed that the relative expression of anti-inflammatory genes (IL-1β, TGF-β) and antioxidant related genes (Nrf2, HO-1) were significantly up-regulated in SWFC groups. Data on intestinal microbiota profile verified that, at the phylum level, the abundance of Fusobacteria was remarkably elevated in the SWFC groups (P < 0.05), whereas the abundance of Firmicutes was declined noteworthy in SWFC0.2 and SWFC0.3 compared to the control group (P < 0.05; P < 0.01) respectively. At the genus level, the abundance of Cetobacterium in the SWFC groups were notably higher than those in the control group (P < 0.05), while the Vibrio content in the SWFC groups was significantly decreased (P < 0.05). PCoA result indicated that the intestinal microflora of SWFC0.2 group was abundant and diverse. Our results elucidate that dietary supplementation of SWFC protects C. carpio from HFD induced inflammatory response and oxidative stress, ameliorate skin mucus, liver and gut health, and improve the gut microbiota balance. Therefore, SWFC could be considered as an improving-fish-health additive, when supplemented to aquatic animal feed. With regards to how SWFC regulates the immunity and inflammatory responses and which signal transductions are involved remains unclear and more scientific evidences are needed to address these issues.

In vitro study of the modulatory effects of heat-killed bacterial biomass on aquaculture bacterioplankton communities

Recent studies have shown that the addition of non-viable microbial biomass or their components (postbiotics) to fish feed can modulate the gut microbiome and positively influence fish health in aquaculture systems. However, no information was hitherto available on the use of non-viable microbial biomass to manipulate aquaculture bacterioplankton communities. To fill this gap, here we used an in vitro model to assess the effects of heat-killed biomasses of an antagonistic strain Pseudoalteromonas rubra SubTr2 and a non-antagonist strain Escherichia coli DH5α on bacterioplankton communities of a recirculating aquaculture system (RAS). Our results showed that these biomasses can have generalist and species-specific effects on aquaculture bacterioplankton structure and function. In addition, they enriched the abundance of bacterial predators, reduced bacterial load and potentially influenced nutrient cycling and pathogen development in aquaculture water. Despite its preliminary nature, for the first time, this study showed that heat-killed microbial biomass has potential application as an in situ modulator of bacterioplankton in aquaculture systems.

The effects of dietary immunostimulants on the innate immune response of Indian major carp: A review

Immunostimulants, as feed additives, play an important role in maintaining fish health and enhancing their overall growth by providing resistance against diseases in cultured fish. At the initial stages of life of fish, innate immunity is the essential mechanism in their survival. Later, innate immunity has an instructive role in adapting acquired immune response and homeostasis through different receptor proteins. Several studies have been conducted to analyze the effect of dietary immunostimulants like algae, plant extracts, vitamins, herbs, probiotics, and prebiotics-containing diets in Indian major carps. Many bacterial, fungal and viral pathogens are responsible for high death rates in both wild and cultured fish. It's a major limiting factor for world aquaculture industries. Recognition of invading pathogens by different pathogen recognition receptor plays an important role for the activation of different pathways to initiate protective immune responses. Hence, there is a growing need to control the devastating effects of diseases without recourse to toxic chemicals or antibiotics. Keeping with alternative approaches without using toxic chemicals to control fish diseases in mind, many immunostimulants are used, which enhance immune responses along with their gene expression level through different signaling pathway. The objective of this review is to summarize and evaluate the current knowledge of various immunostimulants and their immune responses in three Indian major carps namely Catla catla, Labeo rohita and Cirrhinus mrigala, which are preferred by the people.

Comparative Study of Bacillus amyloliquefaciens X030 on the Intestinal Flora and Antibacterial Activity Against Aeromonas of Grass Carp

Beneficial microorganisms to control bacterial diseases has been widely used in aquaculture, Bacillus amyloliquefaciens (BaX030) as a probiotic feed additive was a commonly biological control method. Added sucrose promoted the growth of BaX030, and the yield of its antibacterial substance macrolactin A was enhanced by 1.46-fold. A total of 2055 proteins were screened through proteomics, with 143 upregulated and 307 downregulated. Differential protein expression analysis and qRT-PCR verification showed that the pentose phosphate pathway and the fatty acid synthesis pathway were upregulated, thereby providing sufficient energy and precursors for the synthesis of macrolactin A. The influence of some potential regulatory factors (SecG, LiaI, MecG and ComG) on macrolactin A was discovered. After grass carp were fed with BaX030, the abundance of probiotics (Fusobacterium, Proteobacteria, Gemmobacter) were higher than the control group, and the abundance of potential pathogenic bacteria (Planctomycetes, Aeromonas) were significantly lower than the control group. The cell and challenge experiments showed that BaX030 can significantly increase the expression of C3 and IL8 in the liver and kidney, which decreases the risk of immune organ disease. Moreover, BaX030 effectively reduced the mortality of grass carp. The results revealed that BaX030 can significantly improve the structure of the intestinal flora, enhance immunity and it is beneficial to the control of grass carp Aeromonas.

Dietary Synbiotics Can Help Relieve the Impacts of Deltamethrin Toxicity of Nile Tilapia Reared at Low Temperatures

The optimal water temperature for the normal growth of Nile tilapia is between 26 and 28 °C, and the toxicity of pesticides is strongly related to water temperature. An alternate approach to augmenting the resistance of fish to ambient water toxicity and low water temperature via synbiotic feeding was proposed. In this study, fish were allocated into four groups with 10 fish in each replicate, where they were fed a basal diet or synbiotics (550 mg/kg) and kept at a suboptimal water temperature (21 ± 2 °C). The prepared diets were fed to Nile tilapia for 30 days with or without deltamethrin (DMT) ambient exposure (15 μg/L). The groups were named control (basal diet without DMT toxicity), DMT (basal diet with DMT toxicity), synbiotic (synbiotics without DMT toxicity), and DMT + synbiotic (synbiotics with DMT toxicity). The results displayed upregulated transcription of catalase, glutathione peroxidase, and interferon (IFN-γ) genes caused by DMT exposure and synbiotic feeding when compared with the controls. Moreover, HSP70 and CASP3 genes displayed increased transcription caused by DMT exposure without synbiotic feeding. However, fish fed with synbiotics showed downregulated HSP70 and CASP3 gene expressions. The transcription of IL-1β and IL-8 genes were also decreased by DMT exposure, while fish fed synbiotics showed upregulated levels. DMT exposure resulted in irregular histopathological features in gills, intestine, spleen, and liver tissues, while fish fed synbiotics showed regular, normal, and protected histopathological images. Our results indicated that dietary synbiotics ameliorated histopathological damages in DMT-exposed tilapia through alleviation of oxidative stress and inflammation as well as enhancing the immunity.

Postbiotics and paraprobiotics: A review of current evidence and emerging trends

In recent years, new probiotic-related concepts such as postbiotics and paraprobiotics have been coined to indicate that non-viable microorganisms or bacterial-free extracts may provide benefits to the host by offering additional bioactivities to probiotics, including but not limited to anti-inflammatory, immunomodulatory, anti-proliferative and antioxidant activities. Despite in vitro and in vivo studies that support the promising use of postbiotics and paraprobiotics as health promoters, the mechanism of action and the signaling pathway involved have not yet been fully elucidated. Therefore, the aim of this chapter is to provide an overview of novel probiotic-related concepts and the scientific evidence that supports their bioactivities as well as the possible mechanisms underlying their health-promoting effects. Additionally, current trends in food, feed, and pharmaceutical applications are discussed.

Postbiotics and paraprobiotics: From concepts to applications

In recent years, new probiotic-related concepts such as postbiotics and paraprobiotics have been used to describe non-viable microorganisms or bacterial-free extracts that may provide benefits to the host by offering bioactivities additional to probiotics. However, several aspects related to these postbiotics and paraprobiotics bioactivities remain unexplored or are poorly understood. Therefore, the aim of this work is to provide an overview of the general aspects and emerging trends of postbiotics and paraprobiotics, such as conceptualization of terms, production, characterization, bioactivities, health-promoting effects, bioengineering approaches, and applications. In vitro and in vivo studies have demonstrated that some postbiotics and paraprobiotics exhibit bioactivities such as anti-inflammatory, immunomodulatory, anti-proliferative, antioxidant, and antimicrobial. These bioactivities could be involved in health-promoting effects observed in human and clinical trials, but despite the scientific evidence available, the mechanisms of action and the signaling pathways involved have not been fully elucidated. Nevertheless, paraprobiotics and postbiotics possess valuable potential for the development of biotechnological products with functional ingredients for the nutraceutical industry.

Isolating a new Streptomyces amritsarensis N1-32 against fish pathogens and determining its effects on disease resistance of grass carp

In this study, a Streptomyces strain was isolated from the soil samples of Yanghu Wetland Park in Changsha, Hunan Province. This strain showed excellent antimicrobial activity against 10 fish pathogens, as indicated by the results of the agar-diffusion and oxford cup assays. After 16s rDNA sequencing and physiological & biochemical analyses, it was identified as Streptomyces amritsarensis, namely for S. amritsarensis N1-32. Cytotoxicity test was performed, and the results exhibited that this strain had no toxicity to hepatic L8824 cell line from grass carp liver. The diets supplemented strain N1-32 at concentrations of 1 × 10⁷ cfu/g and 1 × 10⁹ cfu/g was used to feed fish. After 28 days, the expression levels of antioxidant-related genes Nrf2 and Keap1 in the liver and spleen were significantly up-regulated, and the expression of immune-related gene IgM was notably increased in the liver, kidney, head-kidney, and spleen. Toll-like receptor 4 (TLR4) gene expression was up-regulated in the spleen, and TLR4, myeloid differentiation factor 88 (MyD88) gene were up-regulated in the kidney. The survival rate of grass carp was significantly improved after pathogen infection. Whole-genome analysis of N1-32 showed that the strain harbored related genes, capability for producing substances that enhance the immunity of grass carp and inhibit pathogens. A total of 22 gene clusters were identified in the genome, including 5 terpene gene clusters, 4 nonribosomal peptide-synthetase (NRPS) gene clusters and 2 lantipeptide gene clusters. In summary, these results showed that strain N1-32 as a feed additive could regulate grass carp immunity and enhance the resistance of grass carp against fish pathogens.

Time-series transcriptomic analysis of the kelp grouper Epinephelus moara in response to low salinity stress

The Kelp grouper Epinephelus moara is one of the most widely consumed and economically important marine fish in China. The species can tolerate a wide range of salinity, but genomic resources are not available, and the molecular mechanisms underlying adaptation to salinity at the transcriptomic level remain largely unclear. In this study, the transcriptomic responses of the liver of E. moara under low salinity were investigated using the Illumina digital gene expression system. After de novo assembly, 499,356 transcripts were generated and contributed 445,068 unigenes. A total of 14, 19, 33 and 3101 genes were differentially expressed following exposure to low salinity stress for 2, 6, 24 and 48 h, respectively. Only two genes were differentially expressed in all groups. Four genes related to metabolism and ambient salinity adaption were randomly selected to validate the differentially expressed genes (DEGs) by real-time PCR. Gene Ontology (GO) and Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathway enrichment analysis were used to analyse the functional significance of DEGs, including those responding to salinity through diverse biological processes, cellular components, molecular functions, and pathways associated with metabolic and osmotic responses. This work provides new insight into the response to salinity challenges in E. moara, and the findings expand our knowledge of the molecular basis of metabolic regulation mechanisms in this species. Additionally, the transcriptional data provide a valuable resource for future molecular and genetic studies on E. moara.

Dietary Supplementation With a Bacillus Superoxide Dismutase Protects Against γ-Radiation-induced Oxidative Stress and Ameliorates Dextran Sulphate Sodium-induced Ulcerative Colitis in Mice

BACKGROUND AND AIMS

Commercial superoxide dismutase [SOD] is derived from melon extract and has a potential as a dietary supplement due to its beneficial antioxidative effects. We aimed to improve the productivity of SOD compared with plant SOD by using a generally regarded as safe [GRAS] microorganism, Bacillus amyloliquefaciens, and assess its antioxidative effect using γ-radiation- and dextransulphate sodium [DSS]-induced oxidative models in mice.

METHODS

We identified the sodA gene encoding manganese-containing SODs [Mn-SOD] in B. amyloliquefaciens, constructed a Mn-SOD deficient mutant, and screened a high-SOD-producing strain. We compared the antioxidative effect of orally administered enteric-coated SOD protein partially purified from B. amyloliquefaciens with wild-type and high-SOD-producing strain spores. The effect of SOD on DSS-induced colitis was also investigated. Colonic inflammation was assessed using disease activity index, macroscopic and histological damage scores, antioxidant enzyme activities, and inflammatory cytokines.

RESULTS

The SOD activity of B. amyloliquefaciens is derived from secreted Mn-SOD encoded by the sodA gene, as shown by comparing sodA knock-out mutant spores with wild-type and high-SOD-producing spores. Enteric-coated SOD of B. amyloliquefaciens appears to be effective in reducing oxidative stress in γ-radiation- and DSS-induced mouse models. Co-administration of SOD with wild-type B. amyloliquefaciens or high-SOD-producer strain spores showed a synergistic effect. SOD enzyme and B. amyloliquefaciens spores contribute to the reduction of oxidative stress and inflammatory response in DSS-induced colitis.

CONCLUSIONS

Mn-SOD of B. amyloliquefaciens could be another source of SOD supplement and may be useful to prevent and treat ulcerative colitis.

Isolation of Marine Bacillus sp. with Antagonistic and Organic-Substances-Degrading Activities and Its Potential Application as a Fish Probiotic

We report on the isolation and characterization of an acid- and bile-tolerant bacterial strain, Bacillus sp. YB1701 with antibacterial and quorum-quenching activity. Strain YB1701 was isolated from coastal sediment samples and characterized by biochemical tests and 16S rRNA sequencing. In vitro study indicated that strain YB1701 can survive at pH 2.0 for up to 3 h and tolerate bile up to 2.0% concentration even after 12 h of exposure. Strain YB1701 showed antimicrobial activity against fish pathogens Aeromonas hydrophila and Vibrio parahemolyticus using an agar well diffusion assay. The trial test showed dietary supplementation of YB1701 significantly improved the resistance of Carassius auratus gibelio against A. hydrophila challenge. The safety assessment revealed that the isolate Bacillus sp. YB1701 was not cytotoxic to Carassius auratus gibelio or mice and did not exhibit hemolytic activity on rabbit blood agar plate. Disc-diffusion assays using a panel of antibiotics listed by the European Food Safety Authority (EFSA) showed that YB1701 was susceptible to selected antibiotics. Under laboratory conditions, the degradation rate of organic waste (predominately fish excrement) for 14 days by YB1701 was 79.69%. Results from the present study suggest that strain YB1701 is a potential probiotic strain and can be used in aquaculture for degrading organic waste and improving disease resistance of fish against bacterial infection. Further study is needed to assess the utility of strain YB1701 on a commercial scale.