Microbial community characterization of shrimp survivors to AHPND challenge test treated with an effective shrimp probiotic (Vibrio diabolicus)

Updated roles of the gut microbiota in exploring shrimp etiology, polymicrobial pathogens, and disease incidence

Litopenaeus vannamei is the most extensively cultured shrimp species globally, recognized for its scale, production, and economic value. However, its aquaculture is plagued by frequent disease outbreaks, resulting in rapid and massive mortality. etiological research often lags behind the emergence of new diseases, leaving the causal agents of some shrimp diseases unidentified and leading to nomenclature based on symptomatic presentations, especially in cases involving co- and polymicrobial pathogens. Comprehensive data on shrimp disease statuses remain limited. In this review, we summarize current knowledge on shrimp diseases and their effects on the gut microbiome. Furthermore, we also propose a workflow integrating primary colonizers, "driver" taxa in gut networks from healthy to diseased states, disease-discriminatory taxa, and virulence genes to identify potential polymicrobial pathogens. We examine both abiotic and biotic factors (e.g., external and internal sources and specific-disease effects) that influence shrimp gut microbiota, with an emphasis on the "holobiome" concept and common features of gut microbiota response to diverse diseases. After excluding the effects of confounding factors, we provide a diagnosis model for quantitatively predicting shrimp disease incidence using disease common-discriminatory taxa, irrespective of the causal agents. Due to the conservation of functional genes used in designing specific primers, we propose a practical strategy applying qPCR-assayed abundances of disease common-discriminatory functional genes. This review updates the roles of the gut microbiota in exploring shrimp etiology, polymicrobial pathogens, and disease incidence, offering a refined perspective for advancing shrimp aquaculture health management.

Bacterial communities and signatures in the stomach and intestine of juvenile P enaeus (litopenaeus) vannamei shrimp affected by acute hepatopancreatic necrosis disease

Acute hepatopancreatic necrosis (AHPND) is a severe bacterial disease affecting farmed shrimp. Although various pathogenic bacteria associated with AHPND-affected shrimp have been described, little is known about the bacterial signatures in the stomachs and intestines when the disease occurs naturally. In this study, we characterized the microbiome of P. vannamei by high-throughput sequencing (HTS). Shrimp samples were collected from a commercial farm and divided into two groups: healthy and affected by AHPND, confirmed by PCR. Stomach and intestine samples were subjected to microbiome analysis targeting the V3-V4 region of the 16S rRNA gene. PERMANOVA analysis revealed a significant disparity in the bacterial diversity between the stomach and intestine microbiomes of these two health conditions. Our results suggest that the significant abundance of Vibrio brasiliensis and V. sinaloensis in the intestines of affected shrimp plays a role in AHPND infection. This imbalance could be mitigated by the presence of Pseudoalteromonas, Gilvimarinus, and other members of the phylum Pseudomonadota such as Cellvibrionaceae, Psychromonadaceae, and Halieaceae, which showed significant abundance in healthy intestines. This study highlights the significance of the microbial community in the differentiation of specific microbial signatures in different organs of P. vannamei. These findings offer a deeper understanding of the intricate dynamics within the shrimp microbiome under these conditions, enriching our view of AHPND progression and paving the way toward future identification of probiotics tailored for more efficient management of this disease.

The intestine microbiota of shrimp and its impact on cultivation

Intestinal microbiome contains several times of functional genes compared to the host and mediates the generation of multiple metabolic products, and therefore it is called "second genome" for host. Crustaceans rank second among the largest subphylum of aquaculture animals that are considered potentially satisfy global substantial food and nutrition security, among which the Pacific white shrimp (Litopenaeus vannamei) ranks the first in the production. Currently, increasing evidences show that outbreaks of some most devastating diseases in shrimp, including white feces syndrome (WFS) and acute hepatopancreatic necrosis disease (AHPND), are related to intestinal microbiota dysbiosis. Importantly, the intestine microbial composition can be altered by environmental stress, diet, and age. In this review, we overview the progress of intestinal microbiota dysbiosis and WFS or ANPHD in shrimp, and how the microbial composition is altered by external factors. Hence, developing suitable microbial micro-ecological prevention and control strategy to maintain intestinal balance may be a feasible solution to reduce the risk of disease outbreaks. Moreover, we highlight that defining the "healthy intestine microbiota" and evaluating the causality of intestinal microbiota dysbiosis and diseases following the logic of "Microecological Koch's postulates" should be the key goal in future shrimp intestinal field, which help to guide disease diagnosis and prevent disease outbreaks in shrimp farming. KEY POINTS: • Intestinal microbiota dysbiosis is relevant to multiple shrimp diseases. • Microecological Koch's postulates help to evaluate the causality of shrimp diseases.

Insights Into a Chitin Synthase of Kuruma Shrimp Penaeus japonicus and Its Role in Peritrophic Membrane and Cuticle Formation

Synthesis of chitin is a subject of great interest in the fields of physiology and immunology of crustaceans. Chitinous tissues include not only the carapace, but also an acellular membrane in the intestine called the peritrophic membrane (PM). Here, we describe the first report of chitin synthase (CHS) of a penaeid shrimp, kuruma shrimp Penaeus japonicus. Histological observations showed that fecal matter in the midgut of kuruma shrimp was wrapped with a PM, which physically separated it from the midgut epithelium. Subsequently, the chitin synthase transcript was amplified from the midgut of the shrimp. The chitin synthase gene of kuruma shrimp (MjCHS) encodes 1,523 amino acid residues. Structural prediction analysis showed that the N-terminal region of MjCHS protein included nine transmembrane helices, the middle region included the catalytic region with several conserved motifs which are found in CHSs from other arthropods, and the C-terminal region included seven transmembrane helices. Although insects have distinct exoskeletal and intestinal chitin synthases, the phylogenetic analysis suggested that crustaceans have a single CHS. MjCHS mRNA was constantly detected in the digestive tract, including the midgut and hepatopancreas of both juvenile and adult kuruma shrimp, suggesting a stable synthesis of chitin in those organs. In contrast, MjCHS mRNA was also detected in the hindgut and uropod of juvenile shrimp. After molting, the mRNA levels of MjCHS in the stomach and uropod were higher than other molting cycles. These results suggest that MjCHS contributes to chitin synthesis in both the digestive tract and the epidermis, providing fundamental insights into chitin synthesis of crustaceans.

Gut bacterial consortium enriched in a biofloc system protects shrimp against Vibrio parahaemolyticus infection

BACKGROUND

Shrimp cultured in a biofloc system (BFS) have a lower disease incidence than those farmed in a water exchange system (WES). Although a number of studies have reported that the gut bacterial community induced by BFS is highly associated with shrimp disease resistance, the causal relationship remains unknown. Here, the promotive roles of gut bacterial community induced by BFS in pathogenic Vibrio infection resistance and its potential micro-ecological and physiological mechanisms were investigated by gut bacterial consortium transplantation and synthetic community (SynCom) construction.

RESULTS

The BFS induced a more stable and resistant gut bacterial community, and significantly enriched some beneficial bacterial taxa, such as Paracoccus, Ruegeria, Microbacterium, Demequina, and Tenacibaculum. Transplantation of a gut bacterial consortium from BFS shrimp (EnrichBFS) greatly enhanced the stability of the bacterial community and resistance against pathogenic V. parahaemolyticus infection in WES shrimp, while transplantation of a gut bacterial consortium from WES shrimp significantly disrupted the bacterial community and increased pathogen susceptibility in both WES and BFS shrimp. The addition of EnrichBFS in shrimp postlarvae also improved the pathogen resistance through increasing the relative abundances of beneficial bacterial taxa and stability of bacterial community. The corresponding strains of five beneficial bacterial taxa enriched in BFS shrimp were isolated to construct a SynComBFS. The addition of SynComBFS could not only suppress disease development, but also improve shrimp growth, boost the digestive and immune activities, and restore health in diseased shrimp. Furthermore, the strains of SynComBFS well colonized shrimp gut to maintain a high stability of bacterial community.

CONCLUSIONS

Our study reveals an important role for native microbiota in protecting shrimp from bacterial pathogens and provides a micro-ecological regulation strategy towards the development of probiotics to ameliorate aquatic animal diseases. Video Abstract.

Gut microbiota of Pacific white shrimp (Litopenaeus vannamei) exhibits distinct responses to pathogenic and non-pathogenic Vibrio parahaemolyticus

Acute hepatopancreatic necrosis disease (AHPND), a high-mortality-rate shrimp disease, is caused by specific Vibrio parahaemolyticus (Vp) strains with a plasmid encoding the PirABVp toxins. As a bacterial pathogen, the invasion of AHPND-causing Vp might impose pressure on commensal microbiota in the shrimp gut, while the relationship between the pathogenesis of AHPND and the dysbiosis of gut bacterial communities remains unclear. Here we explored the temporal changes of shrimp gut microbiota in response to AHPND-causing and non-AHPND-causing Vp strains, with the non-infected controls as a baseline of the shrimp gut microbiota. The diversity and composition of bacterial communities from 168 gut samples (covering three treatments at seven time points with eight individuals per set) were investigated using 16S rRNA gene metabarcoding with high-throughput sequencing. The results showed that (i) species diversity of gut bacterial communities declined in Vp-infected shrimp, independent of the strain pathogenicity; (ii) taxonomic compositions of gut bacterial communities were significantly different between shrimp infected by AHPND-causing and non-AHPND-causing Vp strains; (iii) short-term (within 6 hours) compositional shifts in the gut microbiota were found only in AHPND-causing Vp-infected shrimp; (iv) the gut microbiota of AHPND-causing Vp-infected shrimp was enriched with genera Photobacterium and Vibrio, with a decline in Candidatus Bacilliplasma; and (v) functional predictions suggested the loss of normal metabolism due to compositional shifts in the gut microbiota. Our work reveals distinct features of community dynamics in shrimp gut microbiota, associated with pathogenic versus non-pathogenic Vibrio infections, providing a new perspective of the pathogenesis of AHPND. IMPORTANCE Shrimp production is continually threatened by newly emerging diseases, such as AHPND, which is caused by specific Vp strains. Previous studies on the pathogenesis of AHPND have mainly focused on the histopathology and immune responses of the host. However, more attention needs to be paid to the gut microbiota, which acts as the first barrier to pathogen colonization. In this study, we revealed that shrimp gut microbiota responded differently to pathogenic and non-pathogenic Vp strains, with bacterial genera Photobacterium and Vibrio enriched in pathogenic Vp-infected shrimp, and Candidatus Bacilliplasma enriched in non-pathogenic Vp-infected shrimp. Moreover, functional predictions suggested that changes in taxonomic compositions would further affect normal metabolic functions, emphasizing the importance of sustaining an equilibrium in the gut microbiota. Several biomarkers associated with specific microbial taxa and functional pathways were identified in our data sets, which help predict the incidence of disease outcomes.

Microbial signature profiles of Penaeus vannamei larvae in low-survival hatchery tanks affected by vibriosis

Vibriosis is caused by some pathogenic Vibrio and produces significant mortality in Pacific white shrimp Penaeus (Litopenaeus) vannamei larvae in commercial hatcheries. Acute hepatopancreatic necrosis disease (AHPND) is an emerging vibriosis affecting shrimp-producing countries worldwide. Zoea 2 syndrome is another type of vibriosis that affects the early stages of P. vannamei larvae. Although the pathogenesis of AHPND and zoea 2 syndrome is well known, there is scarce information about microbial composition and biomarkers of P.vannamei larvae affected by AHPND, and there is no study of the microbiome of larvae affected by zoea 2 syndrome. In this work, we characterized the microbiome of P. vannamei larvae collected from 12 commercial hatchery tanks by high-throughput sequencing. Seven tanks were affected by AHPND, and five tanks were affected by zoea 2 syndrome. Subsequently, all samples were selected for sequencing of the V3-V4 region of the16S rRNA gene. Similarity analysis using the beta diversity index revealed significant differences in the larval bacterial communities between disease conditions, particularly when Vibrio was analyzed. Linear discriminant analysis with effect size determined specific microbial signatures for AHPND and zoea 2 syndrome. Sneathiella, Cyclobacterium, Haliea, Lewinella, among other genera, were abundant in AHPND-affected larvae. Meanwhile, Vibrio, Spongiimonas, Meridianimaribacter, Tenacibaculum, among other genera, were significantly abundant in larvae affected by zoea 2 syndrome. The bacterial network at the phylum level for larvae collected from tanks affected by AHPND showed greater complexity and connectivity than in samples collected from tanks affected by zoea 2 syndrome. The bacterial connections inter Vibrio genera were higher in larvae from tanks affected by zoea 2 syndrome, also presenting other connections between the genera Vibrio and Catenococcus. The identification of specific biomarkers found in this study could be useful for understanding the microbial dynamics during different types of vibriosis.

Evaluation of Bacillus spp. as Potent Probiotics with Reduction in AHPND-Related Mortality and Facilitating Growth Performance of Pacific White Shrimp (Litopenaeus vannamei) Farms

Acute hepatopancreatic necrosis disease (AHPND) is a serious bacterial disease affecting shrimp aquaculture worldwide. In this study, natural microbes were used in disease prevention and control. Probiotics derived from Bacillus spp. were isolated from the stomachs of AHPND-surviving Pacific white shrimp Litopenaeus vannamei (22 isolates) and mangrove forest soil near the shrimp farms (10 isolates). Bacillus spp. were genetically identified and characterized based on the availability of antimicrobial peptide (AMP)-related genes. The phenotypic characterization of all Bacillus spp. was determined based on their capability to inhibit AHPND-causing strains of Vibrio parahaemolyticus (VPAHPND). The results showed that Bacillus spp. without AMP-related genes were incapable of inhibiting VPAHPND in vitro, while other Bacillus spp. harboring at least two AMP-related genes exhibited diverse inhibition activities. Interestingly, K3 [B. subtilis (srfAA+ and bacA+)], isolated from shrimp, exerted remarkable inhibition against VPAHPND (80% survival) in Pacific white shrimp and maintained a reduction in shrimp mortality within different ranges of salinity (75-95% survival). Moreover, with different strains of VPAHPND, B. subtilis (K3) showed outstanding protection, and the survival rate of shrimp remained stable among the tested groups (80-95% survival). Thus, B. subtilis (K3) was further used to determine its efficiency in shrimp farms in different locations of Vietnam. Lower disease occurrences (2 ponds out of 30 ponds) and greater production efficiency were noticeable in the B. subtilis (K3)-treated farms. Taking the results of this study together, the heat-shock isolation and genotypic-phenotypic characterization of Bacillus spp. enable the selection of probiotics that control AHPND in Pacific white shrimp. Consequently, greater disease prevention and growth performance were affirmed to be beneficial in the use of these probiotics in shrimp cultivation, which will sustain shrimp aquaculture and be environmentally friendly.

Genomic and Evolutionary Features of Nine AHPND Positive Vibrio parahaemolyticus Strains Isolated from South American Shrimp Farms

Vibrio parahaemolyticus is a bacterial pathogen that becomes lethal to Penaeus shrimps when acquiring the pVA1-type plasmid carrying the PirABvp genes, causing acute hepatopancreatic necrosis disease (AHPND). This disease causes significant losses across the world, with outbreaks reported in Southeast Asia, Mexico, and South America. Virulence level and mortality differences have been reported in isolates from different locations, and whether this phenomenon is caused by plasmid-related elements or genomic-related elements from the bacteria remains unclear. Here, nine genomes of South American AHPND-causing V. parahaemolyticus (VPAHPND) isolates were assembled and analyzed using a comparative genomics approach at (i) whole-genome, (ii) secretion system, and (iii) plasmid level, and then included for a phylogenomic analysis with another 86 strains. Two main results were obtained from our analyses. First, all isolates contained pVA1-type plasmids harboring the toxin coding genes, and with high similarity with the prototypical sequence of Mexican-like origin, while phylogenomic analysis showed some level of heterogeneity with discrete clusters and wide diversity compared to other available genomes. Second, although a high genomic similarity was observed, variation in virulence genes and clusters was observed, which might be relevant in the expression of the disease. Overall, our results suggest that South American pathogenic isolates are derived from various genetic lineages which appear to have acquired the plasmid through horizontal gene transfer. Furthermore, pathogenicity seems to be a multifactorial trait where the degree of virulence could be altered by the presence or variations of several virulence factors. IMPORTANCE AHPND have caused losses of over $2.6 billion to the aquaculture industry around the world due to its high mortality rate in shrimp farming. The most common etiological agent is V. parahaemolyticus strains possessing the pVA1-type plasmid carrying the PirABvp toxin. Nevertheless, complete understanding of the role of genetic elements and their impact in the virulence of this pathogen remains unclear. In this work, we analyzed nine South American AHPND-causing V. parahaemolyticus isolates at a genomic level, and assessed their evolutionary relationship with other 86 strains. We found that all our isolates were highly similar and possessed the Mexican-type plasmid, but their genomic content did not cluster with other Mexican strains, but instead were spread across all isolates. These results suggest that South American VPAHPND have different genetic backgrounds, and probably proceed from diverse geographical locations, and acquire the pVA1-type plasmid via horizontal gene transfer at different times.

Resilience and probiotic interventions to prevent and recover from shrimp gut dysbiosis

To counter the recurrent outbreaks of bacterial (acute hepatopancreatic necrosis disease; AHPND) and viral (white spot disease; WSD) shrimp diseases, which still remain a threat to the global industry, shrimp gut microbiota research has been gaining more attention in recent years, and the use of probiotics in aquaculture has had promising results in improving shrimp gut health and immunity. In this review based on our studies on AHPND and WSD, we summarize our current understanding of the shrimp gastrointestinal tract and the role of the microbiota in disease, as well as effects of probiotics. We focus particularly on the concept of microbiota resilience, and consider strategies that can be used to restore shrimp gut health by probiotic intervention at a crucial time during gut microbiota dysbiosis. Based on the available scientific evidence, we argue that the use of probiotics potentially has an important role in controlling disease in shrimp aquaculture.

Microbial biomarker detection in shrimp larvae rearing water as putative bio-surveillance proxies in shrimp aquaculture

Background

Aquacultured animals are reared in water hosting various microorganisms with which they are in close relationships during their whole lifecycle as some of these microorganisms can be involved in their host's health or physiology. In aquaculture hatcheries, understanding the interactions existing between the natural seawater microbiota, the rearing water microbiota, the larval stage and the larval health status, may allow the establishment of microbial proxies to monitor the rearing ecosystems. Indeed, these proxies could help to define the optimal microbiota for shrimp larval development and could ultimately help microbial management.

Methods

In this context, we monitored the daily composition of the active microbiota of the rearing water in a hatchery of the Pacific blue shrimp Penaeus stylirostris. Two distinct rearing conditions were analyzed; one with antibiotics added to the rearing water and one without antibiotics. During this rearing, healthy larvae with a high survival rate and unhealthy larvae with a high mortality rate were observed. Using HiSeq sequencing of the V4 region of the 16S rRNA gene of the water microbiota, coupled with zootechnical and statistical analysis, we aimed to distinguish the microbial taxa related to high mortality rates at a given larval stage.

Results

We highlight that the active microbiota of the rearing water is highly dynamic whatever the larval survival rate. A clear distinction of the microbial composition is shown between the water harboring heathy larvae reared with antibiotics versus the unhealthy larvae reared without antibiotics. However, it is hard to untangle the effects of the antibiotic addition and of the larval death on the active microbiota of the rearing water. Various active taxa of the rearing water are specific to a given larval stage and survival rate except for the zoea with a good survival rate. Comparing these communities to those of the lagoon, it appears that many taxa were originally detected in the natural seawater. This highlights the great importance of the microbial composition of the lagoon on the rearing water microbiota. Considering the larval stage and larval survival we highlight that several genera: Nautella, Leisingera, Ruegerira, Alconivorax, Marinobacter and Tenacibaculum, could be beneficial for the larval survival and may, in the rearing water, overcome the r-strategist microorganisms and/or putative pathogens. Members of these genera might also act as probiotics for the larvae. Marivita, Aestuariicocccus, HIMB11 and Nioella, appeared to be unfavorable for the larval survival and could be associated with upcoming and occurring larval mortalities. All these specific biomarkers of healthy or unhealthy larvae, could be used as early routine detection proxies in the natural seawater and then during the first days of larval rearing, and might help to manage the rearing water microbiota and to select beneficial microorganisms for the larvae.

Host-microbiome interaction in fish and shellfish: An overview

The importance of the gut microbiome in the management of various physiological activities including healthy growth and performance of fish and shellfish is now widely considered and being studied in detail for potential applications in aquaculture farming and the future growth of the fish industry. The gut microbiome in all animals including fish is associated with a number of beneficial functions for the host, such as stimulating optimal gastrointestinal development, producing and supplying vitamins to the host, and improving the host's nutrient uptake by providing additional enzymatic activities. Besides nutrient uptake, the gut microbiome is involved in strengthening the immune system and maintaining mucosal tolerance, enhancing the host's resilience against infectious diseases, and the production of anticarcinogenic and anti-inflammatory compounds. Because of its significant role, the gut microbiome is very often considered an "extra organ," as it plays a key role in intestinal development and regulation of other physiological functions. Recent studies suggest that the gut microbiome is involved in energy homeostasis by regulating feeding, digestive and metabolic processes, as well as the immune response. Consequently, deciphering gut microbiome dynamics in cultured fish and shellfish species will play an indispensable role in promoting animal health and aquaculture productivity. It is mentioned that the microbiome community available in the gut tract, particularly in the intestine acts as an innovative source of natural product discovery. The microbial communities that are associated with several marine organisms are the source of natural products with a diverse array of biological activities and as of today, more than 1000 new compounds have been reported from such microbial species. Exploration of such new ingredients from microbial species would create more opportunities for the development of the bio-pharma/aquaculture industries. Considering the important role of the microbiome in the whole life span of fish and shellfish, it is necessary to understand the interaction process between the host and microbial community. However, information pertaining to host-microbiome interaction, particularly at the cellular level, gene expression, metabolic pathways, and immunomodulation mechanisms, the available literature is scanty. It has been reported that there are three ways of interaction involving the host-microbe-environment operates to maintain homeostasis in the fish and shellfish gut i.e. host intrinsic factors, the environment that shapes the gut microbiome composition, and the core microbial community present in the gut system itself has equal influence on the host biology. In the present review, efforts have been made to collect comprehensive information on various aspects of host-microbiome interaction, particularly on the immune system and health maintenance, management of diseases, nutrient uptake, digestion and absorption, gene expression, and metabolism in fish and shellfish.

Selection of Autochthonous Yeasts Isolated from the Intestinal Tracts of Cobia Fish (Rachycentron canadum) with Probiotic Potential

Some yeast strains have been proposed as probiotics to improve the health of cultured fish. Cobia is a tropical benthopelagic fish species with potential for marine aquaculture; however, one of the main limitations to its large-scale production is the high mortality of fish larvae. In this study, we evaluated the probiotic potential of autochthonous yeasts from the intestines of cobia. Thirty-nine yeast isolates were recovered from the intestinal mucosa of 37 adult healthy cobia by culture methods. Yeasts were identified by sequencing of the ITS and D1/D2 regions of the 28S rRNA gene and typed by RAPD-PCR using the M13 primer. Yeast strains with unique RAPD patterns were characterized in terms of their cell biomass production ability; anti-Vibrio, enzymatic, and hemolytic activity; biofilm production; hydrophobicity; autoaggregation; polyamine production; safety; and protection of cobia larvae against saline stress. Candida haemuloni C27 and Debaryomyces hansenii C10 and C28 were selected as potential probiotics. They did not affect the survival of larvae and showed biomass production >1 g L^-1, hydrophobicity >41.47%, hemolytic activity γ, and activity in more than 8 hydrolytic enzymes. The results suggest that the selected yeast strains could be considered as potential probiotic candidates and should be evaluated in cobia larvae.

Dietary supplementation of Pseudoalteromonas piscicida 1UB and fructooligosaccharide enhance growth performance and protect the whiteleg shrimp (Litopenaeus vannamei) against WSSV and Vibrio harveyi coinfection

P. piscicida 1Ub and FOS were evaluated for their potential synbiotic effects on growth, immunological responses, and disease resistance against white spot syndrome virus and V. harveyi coinfection, the major pathogen in whiteleg shrimp aquaculture. Four different supplemented diets were used to feed the experimental shrimp for 40 days: control (control, no probiotic, and prebiotic), probiotic (PRO, P. piscisida 1UB 10⁸ CFU mL^-1), prebiotic (PRE, FOS 0.5% w/w), and the synbiotic (SYN, PRO + PRE). Shrimp's body weight, weight gain, specific growth rate, feed conversion ratio, survival, digestive enzyme activity, and metabolism-related gene expression were all evaluated on day 40. After 40 days, shrimp were infected with WSSV as the primary infection and V. harveyi as the secondary infection 24 h later. Shrimp were then grown for seven days and fed with a control diet. Survival, total hemocyte count (THC), differential hemocyte, phenol-oxidase (PO), respiratory burst activity (RB), and immune-gene expression were all analyzed at 0, 3, and 7 days after infection. The results showed that the PRO, PRE, and SYN supplementation improves whiteleg shrimp growth performance, immune responses, and protection against WSSV and V. harveyi coinfection. The increased activity of digestive enzymes and metabolism-related genes correlates with higher growth performance. The increase in THC, PO, RB, and immune-related gene expression after coinfection was associated with a significant reduction in shrimp mortality. Our findings also suggest that supplementing with synbiotics improves the overall performance of whiteleg shrimp significantly more than probiotics or prebiotics only.

Potential synbiotic effects of a Bacillus mixture and chitosan on growth, immune responses and VP(AHPND) resistance in Pacific white shrimp (Litopenaeus vannamei, Boone, 1931)

The potential synbiotic effects of a Bacillus mixture and chitosan on growth, immune responses and disease resistance against Vibrio parahaemolyticus, the causative agent of acute hepatopancreatic necrosis disease (AHPND) in Pacific white shrimp, were intensively investigated. Three effective strains of Bacillus amyloliquefaciens (A), Bacillus pumilus (P) and Bacillus subtilis (S) were mixed in pairs at a ratio of 5 × 10⁸:5 × 10⁸ CFU/kg diet and coated with the prebiotic chitosan (C) at a concentration of 20 mL/kg diet. Five different feed treatments were used to feed experimental shrimp for 5 weeks: control (control, no synbiotics), chitosan (coat, C) and the synbiotic treatments PAC, PSC and ASC. At week 5, the final length, final weight gain, weight gain, length, average daily gain, specific growth rate and feed conversion ratio, measured as growth parameters, were significantly upregulated in the PSC and ASC groups compared with the control and coat groups (P < 0.05). This result was consistent with the expression analysis of two growth-related genes (Rap-2a and GF-II) in the hepatopancreas and intestines of treated shrimp, as determined using qRT-PCR. The prebiotic chitosan and synbiotics PAC, PSC and ASC strongly induced significant differences in the expression of the Rap-2a and GF-II genes in the target organs compared with the expression in the control group at various time points (P < 0.05). Additionally, application of the synbiotic treatments also significantly enhanced the hepatopancreas characteristics and epithelial and intestinal wall thicknesses of the shrimp compared with the control. Interestingly, all the synbiotic treatments elevated phagocytic activity significantly at weeks 3 and 5 compared with that in the other groups. qRT-PCR analysis of immune-related genes also indicated that the prebiotic group and all synbiotic groups showed strong expression of anti-lipopolysaccharide (ALF) and prophenoloxidase (proPO) genes in the intestine. Finally, the synbiotic groups PAC, PSC and ASC exhibited stronger VP_AHPND resistance at 120 h after exposure than the chitosan coat and control groups, with survival rates of 41.7 ± 11.55, 41.7 ± 0.00, 52.8 ± 5.77, 30.6 ± 15.28 and 22.2 ± 5.77%, respectively (P < 0.05). Based on the obtained information, all synbiotics were recommended for improved growth and immune responses, while ASC was the best for disease resistance against VP_AHPND in Pacific white shrimp.

Bacterial community structure and bacterial isolates having antimicrobial potential in shrimp pond aquaculture

Diseases outbreaks in pond aquaculture have resulted in huge losses to the aquaculture industry. The emergence of non-antimicrobial and environment friendly agents (probiotics) is the potential consideration for the healthy shrimp aquaculture. The present study was aimed to compare the bacterial community compositions in shrimp ponds and surrounding seawater, as well as isolate probiotic bacteria from the shrimp ponds. Based on the high-throughput of 16S rRNA gene sequencing, all sequences were assigned to 3584 unique operational taxonomic units (OTUs) at 97% similarity levels, which were affiliated with 24 phyla, 54 classes, 235 families, and 367 genera. The 10 most abundant phyla were Bacteroidota, Proteobacteria, Actinobacteriota, Planctomycetota, Cyanobacteria, Chloroflexi, Firmicutes, Desulfobacterota, Patescibacteria and Verrucomicrobiota. Notably, the alpha diversity (Shannon diversity) of shrimp ponds was significantly differences (P < 0.05) with that of surrounding seawater. There were 2498 and 791 unique OTUs in shrimp ponds and surrounding seawater, respectively. A total of 15 isolates were obtained in the culturable bacterial diversity, and the antibacterial activities were recorded for potential probiotic bacterial isolates against different tested bacterial isolates including pathogenic bacteria. An isolate Hallobacillusmarinus HMALI004 showed strong inhibitory effects against three pathogenic bacteria, Vibrio cholerae CECT 514, non AHPND V. parahaemolyticus BCRC12959 and AHPND V. parahaemolyticus PD-2. The isolates Algophigussanaruensis AGALI005, Algoriphagus taiwanensis ATALI009 and Bacillusaequororis BAALI008 were also identified as potential probiotics strains.

Control of vibriosis in shrimp through the management of the microbiota and the immune system

Shrimp aquaculture is constantly threatened by recurrent outbreaks of diseases caused by pathogenic bacteria of the genus Vibrio. Acute hepatopancreatic necrosis disease (AHPND) is one of the most aggressive vibriosis reported to date in the shrimp industry. AHPND provokes massive mortalities, causing economic losses with strong social impacts. Control of vibriosis requires the application of multifactorial strategies. This includes vibrio exclusion, shrimp microbiota, particularly in the digestive tract, and shrimp health management through immune stimulation. This paper reviews these two strategies for the prophylactic control of vibriosis. First, we describe the devastating effects of AHPND and the cellular and humoral effectors of the shrimp immune system to cope with this pathology. Secondly, the mechanisms of action of probiotics and their positive impacts are highlighted, including their immunostimulant effects and their role in the balance of the shrimp microbiota. Finally, we reviewed immunostimulants and prebiotics polysaccharides that together with probiotics act benefiting growth, feed efficiency and the microbiota of the digestive tract of farmed shrimp.

Microbiome of Penaeus vannamei Larvae and Potential Biomarkers Associated With High and Low Survival in Shrimp Hatchery Tanks Affected by Acute Hepatopancreatic Necrosis Disease

Acute hepatopancreatic necrosis disease (AHPND) is an emerging bacterial disease of cultured shrimp caused mainly by Vibrio parahaemolyticus, which harbors the lethal PirAB toxin genes. Although Penaeus vannamei (P. vannamei) postlarvae are susceptible to AHPND, the changes in the bacterial communities through the larval stages affected by the disease are unknown. We characterized, through high-throughput sequencing, the microbiome of P. vannamei larvae infected with AHPND-causing bacteria through the larval stages and compared the microbiome of larvae collected from high- and low-survival tanks. A total of 64 tanks from a commercial hatchery were sampled at mysis 3, postlarvae 4, postlarvae 7, and postlarvae 10 stages. PirAB toxin genes were detected by PCR and confirmed by histopathology analysis in 58 tanks. Seven from the 58 AHPND-positive tanks exhibited a survival rate higher than 60% at harvest, despite the AHPND affectation, being selected for further analysis, whereas 51 tanks exhibited survival rates lower than 60%. A random sample of 7 out of these 51 AHPND-positive tanks was also selected. Samples collected from the selected tanks were processed for the microbiome analysis. The V3–V4 hypervariable regions of the 16S ribosomal RNA (rRNA) gene of the samples collected from both the groups were sequenced. The Shannon diversity index was significantly lower at the low-survival tanks. The microbiomes were significantly different between high- and low-survival tanks at M3, PL4, PL7, but not at PL10. Differential abundance analysis determined that biomarkers associated with high and low survival in shrimp hatchery tanks affected with AHPND. The genera Bacillus, Vibrio, Yangia, Roseobacter, Tenacibaculum, Bdellovibrio, Mameliella, and Cognatishimia, among others, were enriched in the high-survival tanks. On the other hand, Gilvibacter, Marinibacterium, Spongiimonas, Catenococcus, and Sneathiella, among others, were enriched in the low-survival tanks. The results can be used to develop applications to prevent losses in shrimp hatchery tanks affected by AHPND.

Effects of the Probiotic Psychrobacter sp. B6 on the Growth, Digestive Enzymes, Antioxidant Capacity, Immunity, and Resistance of Exopalaemon carinicauda to Aeromonas hydrophila

Probiotics, known to improve the water quality and the host's intestinal microbial balance, has gained more and more attention in recent years. The effects of Psychrobacter sp. B6 on the growth and immunity of Exopalaemon carinicauda were investigated in this study. Psychrobacter sp. B6 was sprayed to the basal diet with four different levels (0 [basal diet], 5 × 10⁵, 5 × 10⁷, and 5 × 10⁹ CFU/100 g diet) and were fed to E. carinicauda (average weight 1.15 ± 0.04 g) for 30 days. At the end of the feeding trial, shrimps were immersed in seawater contaminated with 10⁶ CFU/mL pathogenic Aeromonas hydrophila for 2 h and then the cumulative mortality was calculated after 14 days observation. The results showed that the weight gain rate, survival rate, and specific growth rate of E. carinicauda were significantly increased with the increasing dietary level of Psychrobacter sp. B6. The activities of digestive enzymes (α-amylase and chymotrypsin) were significantly increased (P < 0.05) in the groups fed with Psychrobacter sp. B6, and the highest activities of digestive enzymes were detected in the 5 × 10⁹ CFU/100 g diet group. The activities of antioxidant enzymes (catalase, peroxidase, and superoxide dismutase) in probiotics treated shrimp were significantly higher than those in the control shrimp, with the highest activity in 5 × 10⁹ and 5 × 10⁷ CFU/100 g diet group separately. At the same time, the activities of immune-related enzymes (alkaline phosphatase and lysozyme) were significantly affected by the dietary B6 content, and the highest activity of immune-related enzymes was found in shrimps fed with 5 × 10⁷ CFU/100 g diet. The relative expression levels of CTL (C-type lectin), MBL (mannose-binding lectin), SPI (serine protease inhibitor), and ProPo (prophenoloxidase) in hepatopancreas of E. carinicauda with 5 × 10⁹ CFU/100 g diet were significantly higher than those in the control. Moreover, cumulative mortality (22.22%) post-challenge with A. hydrophila was the lowest in 5 × 10⁹ CFU/100 g diet. The results suggested that Psychrobacter sp. B6 could effectively promote the growth, immunity, antioxidant capacity, and disease resistance of E. carinicauda. This study provided a reference for the study on the artificial breeding of E. carinicauda.

Effect of functional diets on intestinal microbiota and resistance to Vibrio parahaemolyticus causing acute hepatopancreatic necrosis disease (AHPND) of Pacific white shrimp (Penaeus vannamei)

AIMS

The present study evaluated the effect of four functional diets and a reference diet on the survival and intestinal bacterial community of shrimp Penaeus vannamei infected with AHPND.

METHODS AND RESULTS

After 42 days of feeding trail, shrimp were inoculated with a Vibrio parahaemolyticus (CIB-0018-3) carrying the plasmid encoding for the PirAB toxins responsible for AHPND. After 120 h post-infection (hpi), shrimp fed with a diet containing 2% of a mix with Curcuma longa and Lepidium meyenii (TuMa) and a diet containing 0.2% of vitamin C (VitC) showed a significantly higher survival (85%) compared to the remaining treatments (50-55%) (p<0.05). Infected shrimp fed with TuMa diet, showed a significant reduction of Vibrionales; and VitC diet promoted an increase of Alteromonadales.

CONCLUSIONS

Our findings suggest that the TuMa diet conferred protection against AHPND and could be attributed to a combined effect of antibacterial properties against Vibrionales, and promoting a desirable bacterial community in the shrimp intestine, while the VitC diet protection could be attributed to their antioxidant capacity and in a lower proportion to a bacterial modulation in shrimp gut.

SIGNIFICANCE AND IMPACT OF THE STUDY

Acute Hepatopancreatic Necrosis Disease (AHPND) is a devastating disease that significantly affects aquaculture production of shrimps. Therefore, the use of functional diets that promotes resistance to AHPND, represents a valuable tool to reduce the mortality of farmed shrimp.

Shrimp AHPND Causing Vibrio anguillarum Infection: Quantitative Diagnosis and Identifying Antagonistic Bacteria

Acute hepatopancreatic necrosis disease (AHPND) is one of the most common and serious diseases in shrimp aquaculture. Relevant works have focused on the gut microbiota-disease relationship when serious AHPND occurs. In contrast, little is known about how the gut microbiota responds to pathogen infection over AHPND progression, whereas this knowledge is fundamental to uncover the etiology of AHPND. Here, we explored the temporal succession of shrimp gut microbiota during Vibrio anguillarum (a causal pathogen of AHPND) challenge. The successful infection of V. anguillarum was confirmed by linearly increased abundance of the pathogen in the shrimp gut over AHPND progression. V. anguillarum infection caused an irreversible disruption in the shrimp gut microbiota, of which infection and hours post infection (hpi) respectively constrained 6.2% and 10.2% of variation in the data. Furthermore, the predicted functional pathways involved in immunity and metabolism significantly decreased, while those facilitating infectious diseases significantly enriched in the infected shrimp. Intriguingly, after ruling out the effect of background changes in gut microbiota, we identified 20 infection-discriminatory taxa that could be served as independent variables for accurately (89.4%) diagnosing V. anguillarum infection, even at the early infection stage, i.e., 24 hpi. Using a consensus network, we identified several Vibrio and Pseudoalteromonas taxa that directly antagonized V. anguillarum, following the Darwin's niche theory. This is one of the few attempts to identify gut bioindicators for diagnosing pathogen infection. In addition, the antagonistic commensals of V. anguillarum might be the candidate probiotics for preventing AHPND.

Aquaculture industry prospective from gut microbiome of fish and shellfish: An overview

The microbiome actually deals with micro-organisms that are associated with indigenous body parts and the entire gut system in all animals, including human beings. These microbes are linked with roles involving hereditary traits, defence against diseases and strengthening overall immunity, which determines the health status of an organism. Considerable efforts have been made to find out the microbiome diversity and their taxonomic identification in finfish and shellfish and its importance has been correlated with various physiological functions and activities. In recent past due to the availability of advanced molecular tools, some efforts have also been made on DNA sequencing of these microbes to understand the environmental impact and other stress factors on their genomic structural profile. There are reports on the use of next-generation sequencing (NGS) technology, including amplicon and shot-gun approaches, and associated bioinformatics tools to count and classify commensal microbiome at the species level. The microbiome present in the whole body, particularly in the gut systems of finfish and shellfish, not only contributes to digestion but also has an impact on nutrition, growth, reproduction, immune system and vulnerability of the host fish to diseases. Therefore, the study of such microbial communities is highly relevant for the development of new and innovative bio-products which will be a vital source to build bio and pharmaceutical industries, including aquaculture. In recent years, attempts have been made to discover the chemical ingredients present in these microbes in the form of biomolecules/bioactive compounds with their functions and usefulness for various health benefits, particularly for the treatment of different types of disorders in animals. Therefore, it has been speculated that microbiomes hold great promise not only as a cure for ailments but also as a preventive measure for the number of infectious diseases. This kind of exploration of new breeds of microbes with their miraculous ingredients will definitely help to accelerate the development of the drugs, pharmaceutical and other biological related industries. Probiotic research and bioinformatics skills will further escalate these opportunities in the sector. In the present review, efforts have been made to collect comprehensive information on the finfish and shellfish microbiome, their diversity and functional properties, relationship with diseases, health status, data on species-specific metagenomics, probiotic research and bioinformatics skills. Further, emphasis has also been made to carry out microbiome research on priority basis not only to keep healthy environment of the fish farming sector but also for the sustainable growth of biological related industries, including aquaculture.