Understanding the roles of surface proteins in regulation of Lactobacillus pentosus HC-2 to immune response and bacterial diversity in midgut of Litopenaeus vannamei

Dietary tryptophan decreases the impacts of seawater temperature changes on behavior and gut health of the sea cucumber Apostichopus japonicus

Seawater temperature change is an important concern for seed production and pond culture of sea cucumbers. The present study found that tentacle activity frequency was significantly lower in sea cucumbers exposed to continuous and rapid temperature increases than that of those at ambient temperature. Feeding behavior directly determines food intake, and further affects physiology and growth efficiency of sea cucumbers. This means that the decline in feeding caused by continuous and rapid temperature increases needs to be addressed in sea cucumber aquaculture. However, a sudden temperature change of 5 °C had no significant effect on behaviors of sea cucumbers. This indicates that continuous temperature increases, rather than a sudden increase, result in behavioral impacts on sea cucumbers. Therefore, we recommend aqua-farmers reduce the feeding amount for sea cucumbers during continuous and rapid temperature increases. In the present study, feeding behavior was significantly higher in sea cucumbers fed with 3% dietary tryptophan than that of those fed with 0% and 5% dietary tryptophan. This indicates that 3% dietary tryptophan increases the food intake of sea cucumbers, and mitigates the feeding decline caused by continuous and rapid temperature increase. This indicates that tryptophan has the potential to promote the feeding of sea cucumbers in seed production and pond culture. Adhesion capacity of sea cucumbers fed with 5% dietary tryptophan was significantly higher than that of individuals fed with 0% and 3% dietary tryptophan. This suggests that dietary tryptophan increases the feeding of sea cucumbers exposed to continuous and rapid temperature increases in pond culture and seed production. In addition, this study found that sea cucumbers fed with 3% dietary tryptophan had higher intestinal colony richness under the continuously rapid temperature change. The present study provides an effective method to improve adhesion behavior and to alleviate the impacts on feeding behavior for seed production and pond culture of sea cucumbers exposed to continuous and rapid temperature increases.

Homologous genes shared between probiotics and pathogens affect the adhesion of probiotics and exclusion of pathogens in the gut mucus of shrimp

Clarifying mechanisms underlying the selective adhesion of probiotics and competitive exclusion of pathogens in the intestine is a central theme for shrimp health. Under experimental manipulation of probiotic strain (i.e., Lactiplantibacillus plantarum HC-2) adhesion to the shrimp mucus, this study tested the core hypothesis that homologous genes shared between probiotic and pathogen would affect the adhesion of probiotics and exclusion of pathogens by regulating the membrane proteins of probiotics. Results indicated that the reduction of FtsH protease activity, which significantly correlated with the increase of membrane proteins, could increase the adhesion ability of L. plantarum HC-2 to the mucus. These membrane proteins mainly involved in transport (glycine betaine/carnitine/choline ABC transporter choS, ABC transporter, ATP synthase subunit a atpB, amino acid permease) and regulation of cellular processes (histidine kinase). The genes encoding the membrane proteins were significantly (p < 0.05) up-regulated except those encoding ABC transporters and histidine kinases in L. plantarum HC-2 when co-cultured with Vibrio parahaemolyticus E1, indicating that these genes could help L. plantarum HC-2 to competitively exclude pathogens. Moreover, an arsenal of genes predicted to be involved in carbohydrate metabolism and bacteria-host interactions were identified in L. plantarum HC-2, indicating a clear strain adaption to host's gastrointestinal tract. This study advances our mechanistic understanding of the selective adhesion of probiotics and competitive exclusion of pathogens in the intestine, and has important implications for screening and applying new probiotics for maintaining gut stability and host health.

Lactobacillus plantarum isolated from kefir enhances immune responses and survival of white shrimp (Penaeus vannamei) challenged with Vibrio alginolyticus

Lactobacillus plantarum is known for its probiotics benefit to host, although the effects vary among strains. This study conducted a feeding experiment of three Lactobacillus strains, MRS8, MRS18 and MRS20, which were isolated from kefir and incorporated into the diets of shrimp to evaluate the effects of non-specific immunity, immune-related gene expression, and disease resistance of white shrimp (Penaeus vannamei) against Vibrio alginolyticus. To prepare the experimental feed groups, the basic feed was mixed with different concentrations of L. plantarum strains MRS8, MRS18, and MRS 20, which were incorporated at 0 CFU (control), 1 × 10⁶ CFU (groups 8-6, 18-6, and 20-6), and 1 × 10⁹ CFU (groups 8-9, 18-9, and 20-9) per gram of diet for an in vivo assay. During the rearing period for 28 days of feeding each group, immune responses, namely the total hemocyte count (THC), phagocytic rate (PR), phenoloxidase activity, and respiratory burst were examined on days 0, 1, 4, 7, 14, and 28. The results showed that groups 20-6, 18-9 and 20-9 improved THC, and groups 18-9 and 20-9 improved phenoloxidase activity and respiratory burst as well. The expression of immunity-related genes was also examined. Group 8-9 increased the expression of LGBP, penaeidin 2 (PEN2) and CP, group 18-9 increased the expression of proPO1, ALF, Lysozyme, penaeidin 3 (PEN3) and SOD, and group 20-9 increased the expression of LGBP, ALF, crustin, PEN2, PEN3, penaeidin 4 (PEN4) and CP (p < 0.05). Groups 18-6, 18-9, 2-6, and 20-9 were further used in the challenge test. After feeding for 7 days and 14 days, Vibrio alginolyticus was injected into white shrimp and observed the shrimp survival for 168 h. The results showed that compared to the control, all groups improved the survival rate. Especially, feeding group 18-9 for 14 days improved the survival rate of white shrimp (p < 0.05). After the challenge test for 14 days, the midgut DNA of survival white shrimps was extracted to analyze the colonization of L. plantarum. Among the groups, (6.61 ± 3.58) × 10⁵ CFU/pre shrimp of L. plantarum in feeding group 18-9 and (5.86 ± 2.27) × 10⁵ CFU/pre shrimp in group 20-9 were evaluated by qPCR. Taken together, group 18-9 had the best effects on the non-specific immunity, the immune-related gene expression, and the disease resistance, which might be due to the benefit of the probiotic colonization.

Infection with white spot syndrome virus affects the microbiota in the stomachs and intestines of kuruma shrimp

Maintaining eubiosis of the gastrointestinal (GI) microbiota is essential for animal health. White spot syndrome virus (WSSV) is the most lethal viral pathogen because it causes extremely high mortality in shrimp farming. However, it remains poorly understood how WSSV infection affects the microbiota in different regions of the GI tract of shrimp. In the present study, we established an experimental model of kuruma shrimp (Marsupenaeus japonicus) infection with WSSV and then investigated the effects of WSSV infection on the microbiota in the cardiac stomach, pyloric stomach, and intestines using metataxonomics. We identified 34 phyla and 576 genera of bacteria collectively. At the phylum level, Proteobacteria and Firmicutes were the most abundant in all the three GI segments. The WSSV infection decreased microbial diversity to a different extent in the stomachs and in a time-dependent manner. The infection with WSSV affected the microbiota composition in the two stomachs, but not the intestines. Firmicutes increased significantly, while Actinobacteria, Bacteroidetes, and Cyanobacteria decreased in the two stomachs of the WSSV-infected shrimp. At the genus level, Trichococcus and Vibrio increased, but Bradyrhizobium and Roseburia decreased in the cardiac stomach of the WSSV-infected shrimp. Trichococcus and Photobacterium increased in the pyloric stomach. Although Vibrio showed a slight downward trend, Aliivibrio (formerly Vibrio) increased in the pyloric stomach. Thiothrix, Fusibacter, and Shewanella decreased in the pyloric stomach, but no significant differences in these genera were detected in the cardiac stomach. Analysis of the predicted functions of the GI microbiota indicated that the WSSV infection resulted in losses of some microbiota functions. The new information from this study may help better understand the bacteria-virus interaction in the GI tract of shrimp and other crustacean species, and inform pathogen prevention/control and sustainable aquaculture production.

Dietary supplementation with Pediococcus pentosaceus enhances the innate immune response in and promotes growth of Litopenaeus vannamei shrimp

To reach the sustainable development goals on health management in Litopenaeus vannamei shrimp culture, Pediococcus pentosaceus AB01 was supplemented in shrimp diet. In this study, the control diet and three experimental diets containing P. pentosaceus AB01 (10⁸ , 10⁹ , 10¹⁰  CFU/g) were separately introduced to L. vannamei for a 28 days feeding trial. After the feeding trial, percent weight gain, feeding efficiency, and feed conversion ratio (FCR) were significantly elevated in L. vannamei administered with P. pentosaceus AB01 at 10⁹ and 10¹⁰ colony-forming unit (CFU)/g. Protease, amylase, and trypsin were found at higher levels in the probiotic-supplied groups. The feeding of shrimps with P. pentosaceus AB01 significantly increased innate immune response and levels of related biochemical parameters in the haemolymph. After the white spot syndrome virus (WSSV) challenge, supplementation of P. pentosaceus AB01 had significant positive effects (p < .05) on survival rate, compared to that of the control diet. The higher resistance of L. vannamei to WSSV might have been due to alterations in the gut microbiome composition and upregulation of the Toll-Like Receptor (TLR) signalling pathway. Hence, P. pentosaceus AB01 may be a promising alternative feed to promote growth rate, modulate microbiota composition, and enhance immunity in L. vannamei shrimp.

Adhesion and Colonization of the Probiotic Lactobacillus plantarum HC-2 in the Intestine of Litopenaeus Vannamei Are Associated With Bacterial Surface Proteins

Surface proteins are a type of proteins expressed on the surface of bacteria that play an important role in cell wall synthesis, maintenance of cell morphology, and signaling with the host. Our previous study showed that the probiotic Lactobacillus plantarum HC-2 improved the growth performance and immune response of Litopenaeus vannamei. To further investigate the probiotic mechanism, we determined the automatic aggregation ability of the bacteria and surface hydrophobicity of HC-2 after being treated with 5 M of lithium chloride (LiCl) and observed the morphology and adhesion of the bacteria to HCT116 cells. The results showed that with the removal of the HC-2 surface protein, the auto-aggregation ability and surface hydrophobicity of HC-2 decreased, and the crude mucus layer coated on the bacterial surface gradually dissociated. The adhesion rate of HC-2 to HCT116 cells decreased from 98.1 to 20.9%. Moreover, a total of 201 unique proteins were identified from the mixture of the surface proteins by mass spectrometry (MS). Several proteins are involved in transcription and translation, biosynthetic or metabolic process, cell cycle or division, cell wall synthesis, and emergency response. Meanwhile, a quantitative real-time PCR qPCR_ showed that HC-2 was mainly colonized in the midgut of shrimp, and the colonization numbers were 15 times higher than that in the foregut, while the colonization rate in the hindgut was lower. The adhesion activity measurement showed that the adhesion level of HC-2 to crude intestinal mucus of L. vannamei was higher than that of bovine serum albumin (BSA) and collagen, and the adhesion capacity of the bacterial cells decreased with the extension of LiCl-treatment time. Finally, we identified the elongation factor Tu, Type I glyceraldehyde-3-phosphate dehydrogenase, small heat shock protein, and 30S ribosomal protein from the surface proteins, which may be the adhesion proteins of HC-2 colonization in the shrimp intestine. The above results indicate that surface proteins play an important role in maintaining the cell structure stability and cell adhesion. Surface proteomics analysis contributes to describing potential protein-mediated probiotic-host interactions. The identification of some interacting proteins in this work may be beneficial to further understand the adhesion/colonization mechanism and probiotic properties of L. plantarum HC-2 in the shrimp intestine.

Exploration of the influence of surface proteins on the probiotic activity of Lactobacillus pentosus HC-2 in the Litopenaeus vannamei midgut via label-free quantitative proteomic analysis

Our previous work showed that using Lactobacillus pentosus HC-2 as a probiotic could improve the growth performance, immune response, gut bacterial diversity and disease resistance of Litopenaeus vannamei. However, the probiotic mechanism had not been fully characterized. In the present study, histology and proteomic analysis were performed to explore the influence of HC-2 surface protein on its probiotic effects on L. vannamei after feeding either the intact surface proteins, the probiotic treated with lithium chloride (LiCl) to remove noncovalently bound surface proteins or no probiotic for four weeks. Histological observation found that feeding with normal HC-2 obviously improved the intestinal histology and enhanced the protective effect against pathogen damage, but feeding with LiCl-treated HC-2 did not improve the intestinal environment. A total of over 2764 peptides and 1118 uniproteins were identified from the L. vannamei midgut; 211 proteins were significantly differentially expressed in the normal HC-2 group compared with the control group; 510 proteins were significantly differentially expressed in the LiCl-treated HC-2 group compared with the control group, and 458 proteins were significantly differentially expressed in the LiCl-treated HC-2 group compared with the normal HC-2 group. GO/KEGG enrichment analysis of the significantly different proteins demonstrated that feeding normal HC-2 mainly induced immune response, metabolic, cell adhesion and cell-cell signaling-related protein upregulation, which contributed to bacterial adhesion and colonization in the midgut to improve the shrimp immune system and growth, but these proteins were suppressed after the shrimp were fed bacteria deprived of surface proteins. Taken together, these results indicate that the surface proteins were indispensable for HC-2 to execute probiotic effects in the shrimp midgut.

The influence of surface proteins on the probiotic effects of Lactobacillus pentosus HC-2 in the Litopenaeus vannamei hepatopancreas

Our previous work showed that Lactobacillus pentosus HC-2 has high antibacterial and adhesion activity, and as a probiotic could improve the nutrients and immunomodulatory effects in the Litopenaeus vannamei farming. In order to further investigate the influence of HC-2 surface protein on its probiotic effects, the immune and digestion related genes expression and enzymes activities, the colonization numbers of HC-2, and the histologic characteristics were analysis in shrimp hepatopancreas after feeding either the intact surface proteins, the probiotic treated with lithium chloride (LiCl) to remove noncovalently bound surface proteins or no probiotic for four weeks. The results showed that the immune genes expression of lysozyme, proPO, LGBP, Penaeidins-3α, crustin and C-type lectin, the immune enzymes activities of superoxide dismutase, catalase and Alkaline phosphatase, and the digestion enzymes of Trypsin, Lipase and α-Amylase were significantly higher in hepatopancreas of shrimp fed with intact HC-2 than that in shrimp fed with base diet or striped surface proteins HC-2 post feeding and challenge. In addition, the shrimp fed with intact HC-2 leads to the bacteria cells adhesion to hepatopancreas was significantly higher than that in shrimp fed with no surface proteins HC-2. Furthermore, the tissue damages of hepatopancreas caused by pathogenic vibrio were obviously observed in shrimp fed with base diet or no surface proteins HC-2, but no signs of damages were found in shrimp fed with intact HC-2. These results demonstrate that surface proteins are important components for HC-2 to execute probiotic effect that improve hepatopancreas immune response and nutrition digestion to protect shrimp against pathogen damage.

Exploring the influence of the surface proteins on probiotic effects performed by Lactobacillus pentosus HC-2 using transcriptome analysis in Litopenaeus vannamei midgut

In order to understand the mediation function of surface proteins in probiotic effects executed by Lactobacillus pentosus HC-2 in midgut of Litopenaeus vannamei, the immune and digestion related enzymes and the transcriptome expression were analyzed after shrimp fed with normal HC-2 or with stripped surface proteins HC-2 by lithium chloride (LiCl) treatment. The results showed that the shrimp fed with normal HC-2 produced much higher immune and digestion related enzymes than the control group or LiCl-treated HC-2 group to defense the Vibrio parahaemolyticus E1 infection. We obtained total over 275,099 unigenes from L. vannamei midgut, 981 genes were significant differentially expressed in normal HC-2 group compared with control, 1314 genes were significant differentially expressed in LiCl-treated HC-2 group compared with control, and 1689 genes were significant differentially expressed in LiCl-treated HC-2 group compared with normal HC-2 group. The GO/KEGG enrichment analysis of the significantly different genes demonstrated that L. vannamei fed with normal HC-2 induced immune-related, signal transduction, ion homeostasis, cell-cell adhesion, response stress/stimulus, vascular endothelial growth factor and peritrophin genes up-regulation, which were important genes involved in improving the shrimp intestine immune response, nutrition and growth performance, and bacteria adhesion and colonization, but these genes were suppressed in the midgut of shrimp fed with deprived surface proteins bacteria. Taken together, these results indicated that the surface proteins were essential for HC-2 executing probiotic effects in midgut of shrimp. Our data contribute to improve the current understanding of host - Lactobacillus interaction and the probiotic mechanisms in shrimps.