Probiotic Bacillus safensis NPUST1 Administration Improves Growth Performance, Gut Microbiota, and Innate Immunity against Streptococcus iniae in Nile tilapia (Oreochromis niloticus)

Effects of Dietary Bacillus amyloliquefaciens SCAU-070 (Based on a Woody Plant-Based Diet) on Antioxidation, Immune and Intestinal Microbiota of Tilapia (Oreochromis niloticus)

This study aimed to explore the effects of Bacillus amyloliquefaciens (BA) as one woody forage addition (as a probiotic, 1 × 107 CFU/g) on tilapia (Oreochromis niloticus). Woody forage is one kind of fishery feed that could significantly enhance the growth, feed utilization, and digestibility of tilapia. At first, tilapia was divided into eight groups and fed with control, control + BA, Moringa oleifera, M. oleifera + BA, Neolamarckia cadamba, N. cadamba + BA, Broussonetia papyrifera, and B. papyrifera + BA diets, respectively. After dieting for 8 weeks, the intestinal morphology of tilapia in the eight groups was observed, and the effects of the B. amyloliquefaciens addition and wordy forage on the intestine functions were analyzed by two-way ANOVA. As no significant negative effects were found on the woody forage on tilapia, the villus height, density and width, and epithelial goblet cells in the posterior intestines of tilapia with BA supplementation were greater than those in the groups without BA supplementation, suggesting B. amyloliquefaciens SCAU-070 could promote the growth and development of tilapia intestinal tracts. Furthermore, it was found that B. amyloliquefaciens SCAU-070 enhanced the antioxidation capacity of tilapia posterior intestine tissue by promoting the activity of superoxide dismutase and content of malondialdehyde. In addition, the result of high-throughput sequencing (16S rDNA) showed that the beneficial bacteria Cetobacterium and Romboutsia in the probiotic groups increased significantly, while the potential pathogenic bacteria Acinetobacter decreased significantly.

Present Status, Limitations, and Prospects of Using Streptomyces Bacteria as a Potential Probiotic Agent in Aquaculture

Streptomyces is a Gram-positive bacterium, belonging to the family Streptomycetaceae and order Streptomycetales. Several strains from different species of Streptomyces can be used to promote the health and growth of artificially cultured fish and shellfish by producing secondary metabolites including antibiotics, anticancer agents, antiparasitic agents, antifungal agents, and enzymes (protease and amylase). Some Streptomyces strains also exhibit antagonistic and antimicrobial activity against aquaculture-based pathogens by producing inhibitory compounds such as bacteriocins, siderophores, hydrogen peroxide, and organic acids to compete for nutrients and attachment sites in the host. The administration of Streptomyces in aquaculture could also induce an immune response, disease resistance, quorum sensing/antibiofilm activity, antiviral activity, competitive exclusion, modification in gastrointestinal microflora, growth enhancement, and water quality amelioration via nitrogen fixation and degradation of organic residues from the culture system. This review provides the current status and prospects of Streptomyces as potential probiotics in aquaculture, their selection criteria, administrative methods, and mechanisms of action. The limitations of Streptomyces as probiotics in aquaculture are highlighted and the solutions to these limitations are also discussed.

Probiotics enhance resistance to Streptococcus iniae in Nile tilapia (Oreochromis niloticus) reared in biofloc systems

Biofloc technology is a rearing technique that maintains desired water quality by manipulating carbon and nitrogen and their inherent mixture of organic matter and microbes. Beneficial microorganisms in biofloc systems produce bioactive metabolites that may deter the growth of pathogenic microbes. As little is known about the interaction of biofloc systems and the addition of probiotics, this study focused on this integration to manipulate the microbial community and its interactions within biofloc systems. The present study evaluated two probiotics (B. velezensis AP193 and BiOWiSH FeedBuilder Syn 3) for use in Nile tilapia (Oreochromis niloticus) culture in a biofloc system. Nine independent 3785 L circular tanks were stocked with 120 juveniles (71.4 ± 4.4 g). Tilapia were fed for 16 weeks and randomly assigned three diets: a commercial control diet or a commercial diet top-coated with either AP193 or BiOWiSH FeedBuilder Syn3. At 14 weeks, the fish were challenged with a low dose of Streptococcus iniae (ARS-98-60, 7.2 × 107  CFU mL-1 , via intraperitoneal injection) in a common garden experimental design. At 16 weeks, the fish were challenged with a high dose of S. iniae (6.6 × 108  CFU mL-1 ) in the same manner. At the end of each challenge trial, cumulative per cent mortality, lysozyme activity and expression of 4 genes (il-1β, il6, il8 and tnfα) from the spleen were measured. In both challenges, the mortalities of the probiotic-fed groups were significantly lower (p < .05) than in the control diet. Although there were some strong trends, probiotic applications did not result in significant immune gene expression changes related to diet during the pre-trial period and following exposure to S. iniae. Nonetheless, overall il6 expression was lower in fish challenged with a high dose of ARS-98-60, while tnfα expression was lower in fish subjected to a lower pathogen dose. Study findings demonstrate the applicability of probiotics as a dietary supplement for tilapia reared in biofloc systems.

Evaluation of dietary single probiotic isolates and probiotic multistrain consortia in growth performance, gut histology, gut microbiota, immune regulation, and infection resistance of Nile tilapia, Oreochromis niloticus, shows superior monostrain performance

The probiotic potential of a designed bacterial consortia isolated from a competitive exclusion culture originally obtained from the intestinal contents of tilapia juveniles were evaluated on Nile tilapia alevins. The growth performance, intestinal histology, microbiota effects, resistance to Streptococcus agalactiae challenge, and immune response were assessed. In addition, the following treatments were included in a commercial feed: A12+M4+M10 (Lactococcus lactis A12, Priestia megaterium M4, and Priestia sp. M10), M4+M10 (P. megaterium M4, and Priestia sp. M10) and the single bacteria as controls; A12 (L. lactis A12), M4 (P. megaterium M4), M10 (Priestia sp. M10), also a commercial feed without any probiotic addition was included as a control. The results showed that all probiotic treatments improved the growth performance, intestinal histology, and resistance during experimental infection with S. agalactiae in comparison to the control fish. Also, the administration of probiotics resulted in the modulation of genes associated with the innate and adaptive immune systems that were non-dependent on microbial colonization. Surprisingly, L. lactis A12 alone induced benefits in fish compared to the microbial consortia, showing the highest increase in growth rate, survival during experimental infection with S. agalactiae, increased intestinal fold length, and the number of differentially expressed genes. Lastly, we conclude that a competitive exclusion culture is a reliable source of probiotics, and monostrain L. lactis A12 has comparable or even greater probiotic potential than the bacterial consortia.

Draft genome sequences of Bacillus pumilus 36R ATNSAL and B. safensis 13L LOBSAL, two potential candidate probiotic strains for shrimp aquaculture

OBJECTIVES

This work aimed to isolate bacterial strains with antagonist activity against Vibrio parahaemolyticus, the causative agent of acute hepatopancreatic necrosis disease (VP_AHPND) that was isolated from outbreaks in Mexico. Here, we report the draft genome sequences of two antagonistic strains, isolated from saline sediment in Sonora, Mexico.

METHODS

Cross-streak and well diffusion tests were employed to find the bacterial strains with higher inhibitory activity against VP_AHPND. The whole genomes of B. pumilus 36R ATNSAL and B. safensis 13L LOBSAL were sequenced using Ion Torrent^TM (PGM) and Illumina Miseq^TM platforms, respectively. Annotation was performed using the RAST server, and the genes involved in the biosynthesis of bacterial secondary metabolites were predicted using antiSMASH.

RESULTS

Two bacterial isolates, B. safensis 13L LOBSAL and B. pumilus 36R ATNSAL, were chosen based on their strong antagonistic profiles. The genome of 36R ATNSAL was 3.94 Mbp in length and contained 3824 genes and a total of 4116 coding sequences (CDSs); the genome of 13L LOBSAL was 3.68 Mbp and contained 3619 genes and 3688 CDSs. Twenty-eight and 32 biosynthetic gene clusters responsible for putative antimicrobial metabolite production were identified in 36R ATNSAL and 13L LOBSAL, respectively.

CONCLUSIONS

The two strains 13L LOBSAL and 36R ATNSAL showed excellent probiotic profiles in vitro. The genome sequences will help with the mining and reconstruction of metabolic pathways in Bacillus strains. Genome sequence-guided strain improvement could augment the probiotic potential of Bacillus strains for applications in shrimp aquaculture.

The Effect of Gut Microbiota and Probiotics on Metabolism in Fish and Shrimp

The present paper presents an overview of the effects of gut microbiota and probiotics on lipid-, carbohydrate-, protein- and amino acid metabolism in fish and shrimp. In probiotic fish studies, the zebrafish (Danio rerio) model is the most frequently used, and probiotic administration reveals the effect on glucose homeostasis, anti-lipidemic effects and increasing short-chain fatty acids, and increased expressions of genes related to carbohydrate metabolism and innate immunity, along with down-regulation of oxidative stress-related genes. Further, improved length of the intestinal villi and expression of nutrient transporters in fish owing to probiotics exposure have been documented. The present review will present an appraisal of the effect of intestinal microbiota and probiotic administration on the metabolism of nutrients and metabolites related to stress and immunity in diverse fish- and shrimp species. Furthermore, to give the reader satisfactory information on the topics discussed, some information from endothermic animals is also presented.

Probiotics Bacillus cereus and B. subtilis reshape the intestinal microbiota of Pengze crucian carp (Carassius auratus var. Pengze) fed with high plant protein diets

The intestinal dysfunction induced by high plant protein diets is frequently observed in farmed fish, and probiotics of Bacillus genus were documented to benefit the intestinal health through the modulation of intestinal microbiota without clearness in its underlying mechanism yet. Fusobacteria, Proteobacteria, and Firmicutes were observed to be the dominate phyla, but their proportion differentiated in the intestinal bacterial community of Pengze crucian carp (Carassius auratus var. Pengze) fed different diets in this study. Dietary supplementation of B. cereus and B. subtilis could reshape the intestinal bacterial community altered by high plant protein diets through a notable reduction in opportunistic pathogen Aeromonas together with an increase in Romboutsia and/or Clostridium_sensu_stricto from Firmicutes. Due to the alteration in the composition of bacterial community, Pengze crucian carp exhibited characteristic ecological networks dominated by cooperative interactions. Nevertheless, the increase in Aeromonas intensified the competition within bacterial communities and reduced the number of specialists within ecological network, contributing to the microbial dysbiosis induced by high plant protein diets. Two probiotics diets promoted the cooperation within the intestinal bacterial community and increased the number of specialists preferred to module hubs, and then further improved the homeostasis of the intestinal microbiota. Microbial dysbiosis lead to microbial dysfunction, and microbial lipopolysaccharide biosynthesis was observed to be elevated in high plant protein diets due to the increase in Aeromonas, gram-negative microbe. Probiotics B. cereus and B. subtilis restored the microbial function by elevating their amino acid and carbohydrate metabolism together with the promotion in the synthesis of primary and secondary bile acids. These results suggested that dietary supplementation of probiotics B. cereus and B. subtilis could restore the homeostasis and functions of intestinal microbiota in Pengze crucian carp fed high plant protein diets.

Dietary SYNSEA probiotic improves the growth of white shrimp, Litopenaeus vannamei and reduces the risk of Vibrio infection via improving immunity and intestinal microbiota of shrimp

The growth performance, immunological status, and intestinal microbiology of white shrimp, Litopenaeus vannamei, were evaluated after dietary administration of the commercial probiotic SYNSEA. Shrimp were fed a control diet (without probiotic supplement) and two levels of SYNSEA probiotic, a low concentration of SYNSEA (LSL) containing 10⁵ CFU (g diet)^-1Bacillus subtilis and 10⁵ CFU (g diet)^-1 lactic acid bacteria (LAB), and a high concentration of SYNSEA (LSH) containing 10⁶ CFU (g diet)^-1B. subtilis and 10⁶ CFU (g diet)^-1 LAB, for 12 weeks. Shrimp fed with the LSL diet significantly increased growth performance as well as final weight and feed efficiency compared to the control, but not the LSH diet. After being orally challenged with Vibrio parahaemolyticus, shrimp fed with LSL diet prior to the challenge or fed with LSL and pathogen simultaneously showed significantly lower mortality compared to the control. SYNSEA probiotic significantly improved shrimp immune response, including lysozyme activity in LSL and LSH groups, and phagocytic activity in the LSL group in comparison to the control. In addition, the gene expressions of anti-lipopolysaccharide factor 2 in LSL and LSH groups, and penaeidin 4 in LSL were also up-regulated. Although there was no significant difference among groups for hepatopancreas and intestinal morphology, the muscular layer thickness and villi height were slightly improved in the intestines of shrimp fed SYNSEA. The 16S rDNA gene amplicon sequence analysis using next-generation sequencing revealed a significant decrease in α-diversity (Margalef's species richness) after oral administration of SYNSEA due to an increase in the relative abundance of beneficial bacteria in the gut flora of shrimp, such as Lactobacillus, Shewanella, and Bradymonadales and a decrease in harmful bacteria, such as Vibrio, Candidatus_Berkiella, and Acinetobacter baumannii. Together the data suggest that the provision of SYNSEA probiotic at 10⁵ CFU (g diet)^-1B. subtilis and 10⁵ CFU (g diet)^-1 LAB can improve shrimp growth, enhance immunity, and disease resistance status of the host. In addition, these findings conclude that SYNSEA probiotic has great preventive and therapeutic potential for Vibrio infection in shrimp aquaculture.

Improvement in the probiotic efficacy of Bacillus subtilis E20-stimulates growth and health status of white shrimp, Litopenaeus vannamei via encapsulation in alginate and coated with chitosan

The aim of this study was to increase the efficacy of probiotic Bacillus subtilis E20 by encapsulating the probiotic in alginate and coating it with chitosan. The protective effect was evaluated by firstly ensuring the viability of encapsulated probiotics in simulated gastrointestinal fluid (SGF) and simulated intestinal fluid (SIF) conditions and then at different storage temperatures. In addition, the encapsulated probiotic was incorporated into the diet to improve the growth performance and health status of white shrimp, Litopenaeus vannamei. B. subtilis E20 has the ability to survive in SGF when encapsulated in 1.5-2% alginate and coated with 0.4% chitosan. Furthermore, viability increased significantly in SIF compared to the probiotic encapsulated in 1% alginate and coated with 0.4% chitosan and the non-encapsulated probiotic. Longer storage time and adverse conditions affected probiotics' survival, which was improved by the encapsulation with significantly higher viability than the non-encapsulated probiotic at different temperatures and storage duration. Encapsulation of B. subtilis E20 and dietary administration at 10⁷ CFU kg^-1 decreased shrimp mortality after a Vibrio infection, thereby improving shrimp's disease resistance, while the non-encapsulated probiotic required 10⁹ CFU kg^-1 to achieve better resistance. Although the best results of growth performance, immune response, and disease resistance against Vibrio alginolyticus were found in the shrimp fed with the diets supplemented with encapsulated probiotic at >10⁸ CFU kg^-1, shrimp's growth performance and health status improved after being fed 10⁷ CFU kg^-1 encapsulated probiotic for 56 days. Together, the results of this study prove that encapsulation could improve the viability of probiotic in different gastrointestinal conditions and adverse storage temperatures. Overall, lower concentrations of encapsulated probiotic B. subtilis E20 (10⁷ CFU kg^-1) was able to increase the growth performance and health status of shrimp.