Evaluation of Lactococcus lactis HNL12 combined with Schizochytrium limacinum algal meal in diets for humpback grouper (Cromileptes altivelis)

Transgenic Schizochytrium as a Promising Oral Vaccine Carrier: Potential Application in the Aquaculture Industry

Schizochytrium limacinum SR21, a kind of eukaryotic heterotrophic organism rich in unsaturated fatty acids, is an emerging microbial alternative to fish oil. The dietary inclusion of 15% SR21 was optimal for the growth performance of zebrafish. Previous studies demonstrated that fructose-1,6-bisphosphate aldolase (FBA) of Edwardsiella tarda is a valuable broad-spectrum antigen against various pathogens in aquaculture (e.g., Aeromonas hydrophila, Vibro anguillarum, Vibro harveyi, Vibro alginolyticus). We pioneered the development of stable S. limacinum SR21 transformants expressing the antigen protein FBA, exploring their potential as a novel oral vaccine for the aquaculture industry. The model animal zebrafish (Danio rerio) and ornamental fish koi carp (Cyprinus carpio koi) were harnessed to assess the immunoprotective effect, respectively. According to the quantitative expression analysis, zebrafish fed with recombinant Schizochytrium expressing FBA exhibited specific immune responses in the intestine. The expression levels of MHC-I and MHC-II, involved in cell-mediated adaptive immune responses, were significantly upregulated on the 14th and 28th days post-immunization. Additionally, the expression of highly specialized antibody genes IgZ1 and IgZ2 in mucosal immunity were significantly triggered on the 14th day post-immunization. Feeding koi carp with recombinant S. limacinum SR21-FBA increased the production of myeloperoxidase and FBA-specific antibodies in the sera. Furthermore, the sera of koi fed with recombinant S. limacinum SR21-FBA exhibited significant bactericidal activities against pathogen E. tarda. Thus, S. limacinum SR21 is a natural and highly promising oral vaccine carrier that not only provides essential nutrients as a functional feed ingredient but also offers specific immune protection to aquatic animals. This dual application is vital for promoting the sustainable development of the aquaculture industry.

Influence of a Mixture of Protein Hydrolysate from Black Soldier Fly Larvae and Schizochytrium on Palatability, Plasma Biochemistry, and Antioxidative and Anti-Inflammatory Capacity in Cat Diets

The objective of this research was to evaluate palatability, plasma biochemistry, antioxidative and anti-inflammatory capacity, and immune levels in cats by feeding supplementing inclusion of different levels of a mixture of protein hydrolysate from black soldier fly larvae and schizochytrium (BSFPs) in diets. In the feed experiment, a total of 24 adult cats (12 females and 12 males; BW: 3.02 ± 0.06 kg) were randomly divided into four groups: (1) diet with chicken and fish meal as primary protein resource (CON); (2) diet with 5% BSFPs replacing chicken meal, fish meal, chicken oil, and fish oil (5% BSFPs); (3) 10% BSFPs; and (4) 15% BSFPs. The body weight and feed intake were recorded, and a blood sample was collected for analysis. In the palatability experiment, three diets containing 5%, 10%, and 15% BSFPs were evaluated by comparing with CON. These results suggested that different levels of BSFPs could improve palatability in cat diets by enhancing the first sniff, the first bite, and feed intake (p < 0.05). However, no significant influence existed in body weight and average daily feed intake (p > 0.05). In comparison to the CON group, 5% and 15% BSFPs significantly increased the total protein content, and all treatment groups decreased the triglyceride content and enhanced the calcium concentration in plasma; in addition, the activity of aspartate aminotransferase and alanine aminotransferase and the content of creatinine and urea nitrogen were significantly reduced by the supplementation inclusion of BSFPs in the diets (p < 0.05). The enzyme activity of glutathione peroxidase was dramatically enhanced by the supplementation of 10% and 15% BSFPs in diets compared with the CON diet, and the activity of superoxide dismutase was increased and the malondialdehyde concentration was remarkably reduced in all three treatments (p < 0.05). Compared with the CON group, different levels of BSFPs in the diets significantly increased the immunoglobulin A content in plasma; similarly, the immunoglobulin G concentration was significantly enhanced by the supplementation of 10% and 15% BSFPs in the diets (p < 0.05). Furthermore, the interleukin-1β content was significantly reduced in the inclusion of 10% and 15% BSFPs in the diets, and 15% BSFPs remarkably decreased the content of interleukin-8 in plasma compared with the CON diet (p < 0.05). To sum up, the supplementation of different levels of BSFPs exhibited a positive effect on palatability and enhanced the antioxidant, anti-inflammatory, and immune capacity. Particularly, the addition levels of 10% and 15% BSFPs were more effective in antioxidation, anti-inflammation, and immunity.

Chromosome-level genome assembly of humpback grouper using PacBio HiFi reads and Hi-C technologies

The humpback grouper (Cromileptes altivelis), a medium-sized coral reef teleost, is a naturally rare species distributed in the tropical waters of the Indian and Pacific Oceans. It has high market value, but artificial reproduction and breeding remain limited and need to be improved. Here, we assembled the genome with 1.08 Gb, with a contig N50 of 43.78 Mb. A total of 96.59% of the assembly anchored to 24 pseudochromosomes using Hi-C technology. It contained 24,442 protein-coding sequences, of which 99.3% were functionally annotated. The completeness of the assembly was estimated to be 97.3% using BUSCO. The phylogenomic analysis suggested that humpback grouper should be classified into the genus Epinephelus rather than Cromileptes. The comparative genomic analysis revealed that the gene families related to circadian entrainment were significantly expanded. The high-quality reference genome provides useful genomic tools for exploiting the genomic resource of humpback grouper and supports the functional genomic study of this species in the future.

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.

Probiotics and Immunostimulant modulate intestinal flora diversity in Reeves pond tortoise (Mauremys reevesii) and effects of Clostridium butyricum on its spleen transcriptome

In this study, we investigated the effects of Clostridium butyricum (group A), Bacillus subtilis (group B), and the immune enhancer algal β-1,3 glucan (group C) on the intestinal flora of Mauremys reevesii and the effects of C. butyricum on the transcriptome of M. reevesii splenic immune tissues. M. reevesii were assigened to four groups, each containing three replicates from 18 samples. Juvenile turtles with an initial weight of 106.35 ± 0.03 g were fed a basic diet containing no probiotics (control group D), or a basic diet containing the A, B, or C supplement. After the turtles had been fed for 60, 90, and 120 d of the experimental period, high-throughput sequencing of the 16S rRNA gene revealed no significant difference in alpha diversity among the four groups at 60 days of feeding (P > 0.05), and at 90 days, the alpha diversity in group A was significantly different (P < 0.05), with an increase of 26.62% in the Shannon index and a decrease of 83.33% in the Simpson index; at 120 d, the alpha diversity (Shannon index)showed a decreasing trend in order for groups A, B, and C, At the phylum level, the abundance of Bacteroidetes, Proteobacteria, and Fusobacteria in group A increased significantly with increasing feeding time (P < 0.05)，At the genus level, the abundance of Ruminococcaceae and Anaerotruncus in group A increased significantly compared with that in the other three groups (P < 0.05). Transcriptome analysis showed that 384 genes were differentially expressed in the spleen of M. reevesii, 195 genes were upregulated and 189 genes were downregulated, and C. butyricum TF201120 regulated the hematopoietic cell lineage signaling pathway in the spleen of M. reevesii (P < 0.05). The regulation of several identified immune-related genes was confirmed by qPCR, These results showed that C. butyricum, B. subtilis and the immune enhancer algal β-1,3 glucan can improve the intestinal flora of M. reevesii, with C. butyricum TF20 being the most effective and significantly enhancing the immunity of M. reevesii.

Effect of Tributyrin on Growth Performance and Pathway by which Tributyrin Regulates Oligopeptide Transporter 1 in Juvenile Grass Carp (Ctenopharyngodon idellus)

Simple Summary

Oligopeptide transporter 1 (PepT1) plays a role in the transportation and absorption of oligopeptides, which is an important part of protein nutrition and affects the growth of animals. Tributyrin (TB), the precursor of butyrate, exhibits similar functions to those of the butyrate in intestinal nutrients absorption. The analysis of TB on the growth of grass carp and its regulation pathway on PepT1 may help us to better understand the functions of TB and oligopeptide transportation via PepT1, which can be modulated by diet. In this study, we demonstrated that an appropriate level of tributyrin supplementation in the diet promoted the growth of juvenile grass carp and elevated the expressions of caudal type homeobox 2 (CDX2), specificity protein 1 (SP1), and PepT1 in the grass carp intestine and primary intestine cell. In addition, CDX2 and SP1 regulating the expression of PepT1 was investigated. Finally, CDX2/SP1-mediating tributyrin regulation on PepT1 was elucidated. This study verified the effect of tributyrin on the growth of juvenile grass carp and clarified the tributyrin regulation pathway on CDX2/SP1-PepT1.

Abstract

The nutritional functions of tributyrin (TB) have been extensively studied, but questions remain regarding its influence on the growth of juvenile grass carp (Ctenopharyngodon idellus) and the regulation pathway to PepT1 in the intestine of grass carp. To answer the remaining questions, feeding trials, cell trials, and peritoneal injection trials were conducted in this study. The results showed that an appropriate level of TB (0.5 g/kg and 1.0 g/kg) supplementation in feed significantly promoted the growth performance of juvenile grass carp. The expressions of intestine genes (CDX2, SP1 and PepT1) related to oligopeptide transportation increased in the 0.5 g/kg TB group of feeding trials and both the 5 mM and 10 mM TB groups of the intestine cell trials, respectively. Subsequently, the injection trials of inhibitors CDX2 and SP1 demonstrated that the inhibition of CDX2 or SP1 decreased the mRNA expression of PepT1. Finally, the results of independent or combined treatments of TB and the inhibitors suggested that CDX2/SP1 mediated TB regulation on PepT1. These findings may help us to better understand the functions of TB on growth and PepT1 oligopeptide transportation, which could be modulated by dietary TB through the CDX2/SP1-PepT1 pathway in juvenile grass carp.

Comparison of Biochemical Composition and Non-Volatile Taste Active Compounds of Back and Abdominal Muscles in Three Marine Perciform Fishes, Chromileptes altivelis, Epinephelus akaara and Acanthopagrus schlegelii

Humpback grouper Chromileptes altivelis (HG), red-spotted grouper Epinephelus akaara (RG) and black seabream Acanthopagrus schlegelii (BS) are three popular perciform fishes with an increasingly important farming industry. The prices of BS are much lower than other grouper species; however, the differences in the nutritive values of these three perciform fishes with commercial specifications have not been reported. In this study, the biochemical composition and non-volatile taste active compounds of adult HG, RG and BS were investigated. Moisture contents in BS were significantly higher than in HG and RG (p < 0.05), and relatively lower crude protein contents in BS were observed. Lipid contents of back muscle were lower than that of abdomen muscle in the three fish species. C22:6n-3 (DHA) was the major poly-unsaturated fatty acid (PUFA) in HG and BS, while the main PUFA in RG was C18:2n-6. The total healthy omega-3 fatty acid (Σn-3) profiles in HG were the highest (24.08−24.59%), followed by RG (18.24−19.06%) and BS (13.63−15.91%) (p < 0.05). Glycine was the most abundant free amino acid (FAA) in HG and RG, while lysine was the major FAA in BS. Equivalent umami concentration (EUC) values in BS were the highest, followed by HG and RG (p < 0.05). Lactic acid and PO43− were the major organic acids and inorganic ions, respectively. In conclusion, HG and RG provided more protein and healthy omega-3 fatty acids than BS, while BS had a stronger umami taste according to the EUC values.

Antimicrobial activity and mechanisms of a derived antimicrobial peptide TroNKL-27 from golden pompano (Trachinotus ovatus) NK-lysin

NK-lysin, a homologue of granulysin among human, is predominantly found in natural killer cells and cytotoxic T-lymphocytes, which plays a pivotal part in innate immune responses against diverse pathogenic bacteria. Nonetheless, in teleosts, the research on antimicrobial activity and mechanisms of NK-lysin are seldom reported. In this study, we determined the antimicrobial activity of the truncated peptide TroNKL-27 that derived from golden pompano (Trachinotus ovatus) NK-lysin, and investigated its antimicrobial mechanisms. The results showed that TroNKL-27 had considerable antimicrobial potency against both Gram-positive (Staphylococcus aureus, Streptococcus agalactiae) and Gram-negative bacteria (Vibrio harveyi, V. alginolyticus, Escherichia coli, Edwardsiella tarda). Cytoplasmic membrane depolarization and propidium iodide (PI) uptake assay manifested that TroNKL-27 could induce the bacterial membrane depolarization and change its membrane permeability, respectively. In the light of scanning electron microscopy (SEM) observation, TroNKL-27 was capable of altering morphological structures of bacteria and leading to leakage of cellular contents. Moreover, the results of gel retardation assay indicated TroNKL-27 had the ability to induce the degradation of bacterial genomic DNA. As regards in vivo assay, TroNKL-27 could reduce the replication of V. harveyi in tissues of golden pompano, protect the tissue from pathological changes. Moreover, TroNKL-27 in vivo could significantly increase the expression of the immune genes (such as IL1β, TNFα, IFN-γ, C3 and Mx) in presence or absence of V. harveyi infection. All of these results suggest that TroNKL-27 is a novel antimicrobial peptide possessing antibacterial and immunoregulatory function in vivo and in vitro, and the observed effects of TroNKL-27 will lay a solid foundation for the development of new antimicrobial agents used in aquaculture.

An established kidney cell line from humpback grouper (Cromileptes altivelis) and its susceptibility to bacteria and heavy metals

Humpback grouper (Cromileptes altivelis), one kind of commercial fish with considerable economic value, has been recognized as a promising candidate for mariculture. In the wake of the development of aquaculture industry, the breeding density of C. altivelis has increased gradually, which gave rise to the occurrence of various pathogenic diseases. In our research, we established a new kidney cell line (designated as CAK) from humpback grouper and evaluated its susceptibility to bacteria and heavy metals. The results of our study showed that the optimal growth temperature was 26 °C, and optimal medium was L-15 supplemented with 20% fetal bovine serum (FBS). The sequencing of 18S rRNA gene indicated that CAK cell line was derived from C. altivelis. Chromosome analysis showed that the number of chromosome in CAK was 48. After being transfected of pEGFP-N3 plasmid, high transfection efficiency of CAK was observed, suggesting the potential to be used for the study of foreign functional genes. Moreover, the bacterial susceptibility results revealed that CAK cells were sensitive to Vibrio harveyi and Edwardsiella tarda, especially V. harveyi. Meanwhile, three heavy metals (Hg, Cu, and Cd) had toxic effects on the CAK cells with a dose-dependent manner. To sum up, the CAK cell line might be an ideal tool in vitro for analyzing the function of exogenous genes, bacterial susceptibility, and toxicity assay of heavy metals.

Establishment of a new fish cell line from the brain of humpback grouper (Cromileptes altivelis) and its application in toxicology and bacterial susceptibility

Cromileptes altivelis, humpback grouper, belongs to the family Epinephelidae and is one popular farmed fish species because of its high economic value and ornamental value. However, more and more diseases outbreaks have been reported with C. altivelis aquaculture. Today, a new brain cell line of C. altivelis (named CAB) was established and characterized. Our results showed that CAB cells were suitable for growth at 26 °C in L-15 medium supplemented with 15% fetal bovine serum (FBS). The results of 18S rRNA gene sequencing confirmed that CAB cell line was derived from C. altivelis. Moreover, chromosomal aneuploidy was observed in CAB cells, and the modal chromosome number of CAB cells was 48 by chromosome analysis. In addition, CAB cells could transfect pEGFP-N3 plasmid with high transfection efficiency, indicating that CAB cell line has the potential to investigate the function of exogenous genes in vitro. Furthermore, the bacterial susceptibility results suggested that CAB cells were susceptive to Vibrio harveyi and Edwardsiella tarda. And, heavy metals (Hg, Cd, and Cu) were toxic to the CAB cells, and the toxic effect was dose-dependent. In summary, the CAB cell line could be a powerful tool in vitro to study functional genes and has the potential application in bacterial susceptibility and toxicology.

Establishment and characterization of a new cell line from the muscle of humpback grouper (Cromileptes altivelis)

The humpback grouper (Cromileptes altivelis) is a commercially important species of the family Epinephelidae. With the development in aquaculture industry, C. altivelis breeding has gradually increased in volumetric production, leading to the occurrence of various diseases. In this study, we established a new cell line (CAM) derived from the muscle tissue of C. altivelis. Our results showed that the optimal growth temperature and working concentration of fetal bovine serum (FBS) of CAM cells were 28 °C and 15%, respectively. DNA sequencing and comparative analysis of 18S rRNA gene sequence showed that CAM cell line was originated from C. altivelis. Chromosome analysis showed that the modal chromosome number of CAM cells was 48. After transfection using pEGFP-N3 plasmid, CAM cells exhibited high transfection efficiency, indicating that CAM cells could be used in foreign gene expression studies. Further, cytotoxicity analysis revealed that CAM cells were sensitive to Vibrio harveyi and Edwardsiella tarda. Moreover, the cytotoxicity of heavy metals (Hg, Cd, and Cu) to CAM cells was dose-dependent. This CAM cell line might be used as an ideal tool in vitro for analyzing and understanding the mechanisms of pathogenesis, host-pathogen interactions, and toxicity assay of heavy metals.

Update of the list of QPS-recommended biological agents intentionally added to food or feed as notified to EFSA 11: suitability of taxonomic units notified to EFSA until September 2019

Qualified presumption of safety (QPS) was developed to provide a generic safety evaluation for biological agents to support EFSA's Scientific Panels. The taxonomic identity, body of knowledge, safety concerns and antimicrobial resistance are assessed. Safety concerns identified for a taxonomic unit (TU) are where possible to be confirmed at strain or product level, reflected by 'qualifications'. No new information was found that would change the previously recommended QPS TUs and their qualifications. The list of microorganisms notified to EFSA was updated with 54 biological agents, received between April and September 2019; 23 already had QPS status, 14 were excluded from the QPS exercise (7 filamentous fungi, 6 Escherichia coli, Sphingomonas paucimobilis which was already evaluated). Seventeen, corresponding to 16 TUs, were evaluated for possible QPS status, fourteen of these for the first time, and Protaminobacter rubrum, evaluated previously, was excluded because it is not a valid species. Eight TUs are recommended for QPS status. Lactobacillus parafarraginis and Zygosaccharomyces rouxii are recommended to be included in the QPS list. Parageobacillus thermoglucosidasius and Paenibacillus illinoisensis can be recommended for the QPS list with the qualification 'for production purposes only' and absence of toxigenic potential. Bacillus velezensis can be recommended for the QPS list with the qualification 'absence of toxigenic potential and the absence of aminoglycoside production ability'. Cupriavidus necator, Aurantiochytrium limacinum and Tetraselmis chuii can be recommended for the QPS list with the qualification 'production purposes only'. Pantoea ananatis is not recommended for the QPS list due to lack of body of knowledge in relation to its pathogenicity potential for plants. Corynebacterium stationis, Hamamotoa singularis, Rhodococcus aetherivorans and Rhodococcus ruber cannot be recommended for the QPS list due to lack of body of knowledge. Kodamaea ohmeri cannot be recommended for the QPS list due to safety concerns.

Scientific Opinion on the update of the list of QPS-recommended biological agents intentionally added to food or feed as notified to EFSA (2017-2019)

The qualified presumption of safety (QPS) was developed to provide a safety pre-assessment within EFSA for microorganisms. Strains belonging to QPS taxonomic units (TUs) still require an assessment based on a specific data package, but QPS status facilitates fast track evaluation. QPS TUs are unambiguously defined biological agents assessed for the body of knowledge, their safety and their end use. Safety concerns are, where possible, to be confirmed at strain or product level, and reflected as 'qualifications'. Qualifications need to be evaluated at strain level by the respective EFSA units. The lowest QPS TU is the species level for bacteria, yeasts and protists/algae, and the family for viruses. The QPS concept is also applicable to genetically modified microorganisms used for production purposes if the recipient strain qualifies for the QPS status, and if the genetic modification does not indicate a concern. Based on the actual body of knowledge and/or an ambiguous taxonomic position, the following TUs were excluded from the QPS assessment: filamentous fungi, oomycetes, streptomycetes, Enterococcus faecium, Escherichia coli and bacteriophages. The list of QPS-recommended biological agents was reviewed and updated in the current opinion and therefore now becomes the valid list. For this update, reports on the safety of previously assessed microorganisms, including bacteria, yeasts and viruses (the latter only when used for plant protection purposes) were reviewed, following an Extensive Literature Search strategy. All TUs previously recommended for 2016 QPS list had their status reconfirmed as well as their qualifications. The TUs related to the new notifications received since the 2016 QPS opinion was periodically evaluated for QPS status in the Statements of the BIOHAZ Panel, and the QPS list was also periodically updated. In total, 14 new TUs received a QPS status between 2017 and 2019: three yeasts, eight bacteria and three algae/protists.