Dietary Supplementation of Bacillus sp. PM8313 with β-glucan Modulates the Intestinal Microbiota of Red Sea Bream (Pagrus major) to Increase Growth, Immunity, and Disease Resistance

Effects of host-associated low-temperature probiotics in olive flounder (Paralichthys olivaceus) aquaculture

This study investigated the effects of supplementation of low-temperature probiotics isolated from the intestines of olive flounder on the growth performance, digestibility, and regulation of intestinal microbiota and the expression of genes related to growth, immunity, and apoptosis in olive flounder. Bacteria showing high growth at approximately 15-20 °C, which is the temperature of olive flounder culture, were isolated and confirmed to be Pseudomonas species through 16S rRNA gene sequence analysis. Whole-genome sequencing revealed that the strain has a 6,195,122 bp single circular chromosome and a guanine-cytosine content of 59.9%. In the feeding trial, supplementation with 1 × 108 CFU/g of the isolate strain positively modulated growth performances, digestive enzyme activity, and gut microbiota composition of olive flounder. RT-qPCR for the comparison of growth, immunity, and apoptosis-related gene expression levels showed no significant differences between the groups. Therefore, the isolated host-associated low-temperature probiotics improved the growth performance of olive flounder by causing positive changes in digestive activity and intestinal microbial composition without affecting host gene expression.

Effects of β-1,3-glucan on growth, immune responses, and intestinal microflora of the river prawn (Macrobrachium nipponense) and its resistance against Vibrio parahaemolyticus

In this study, we investigated the impact of β-1,3-glucan on the immune responses and gut microbiota of the river prawn (Macrobrachium nipponense) in the presence of Vibrio parahaemolyticus stress. Shrimps were fed one of the following diets: control (G1), 0.2% curdlan (G2), 0.1% β-1,3-glucan (G3), 0.2% β-1,3-glucan (G4), or 1.0% β-1,3-glucan (G5) for 6 weeks and then challenged with V. parahaemolyticus for 96 h. Under Vibrio stress, shrimps in G4 exhibited the highest length gain rate, weight gain rate, and survival rate. They also showed increased intestinal muscle thickness and villus thickness compared to the control and 0.2% curdlan groups. The apoptosis rate was lower in G4 than in the control group, and the digestive enzyme activities (pepsin, trypsin, amylase, and lipase), immune enzyme activities (acid phosphatase, alkaline phosphatase, lysozyme, and phenoxidase), and energy metabolism (triglyceride, cholesterol, glycogen, and lactate dehydrogenase) were enhanced. Expression levels of growth-related genes (ecdysone receptor, calmodulin-dependent protein kinase I, chitin synthase, and retinoid X receptor) and immune-related genes (toll-like receptor 3, myeloid differentiation primary response 88, mitogen-activated protein kinase 7, and mitogen-activated protein kinase 14) were higher in G4 than in the control. Microbiota analysis indicated higher bacterial abundance in shrimps fed β-1,3-glucan, as evidenced by Sob, Chao1, and ACE indices. Moreover, 0.2% β-1,3-glucan increased the relative abundances of Bacteroidota and Firmicutes while reducing those of Corynebacteriales and Lactobacillales. In summary, β-1,3-glucan enhances immune enzyme activities, alters immune-related gene expression, and impacts gut microbial diversity in shrimp. These findings provide valuable insights into the mechanisms underlying β-1,3 glucan's immune-enhancing effects.

Ability of Lactobacillus brevis 47f to Alleviate the Toxic Effects of Imidacloprid Low Concentration on the Histological Parameters and Cytokine Profile of Zebrafish (Danio rerio)

In the present article, the possible mitigation of the toxic effect of imidacloprid low-concentration chronic exposure on Danio rerio by the probiotic strain Lactobacillus brevis 47f (1 × 108 CFU/g) was examined. It was found that even sublethal concentration (2500 µg/L) could lead to the death of some fish during the 60-day chronic experiment. However, the use of Lactobacillus brevis 47f partially reduced the toxic effects, resulting in an increased survival rate and a significant reduction of morphohistological lesions in the intestines and kidneys of Danio rerio. The kidneys were found to be the most susceptible organ to toxic exposure, showing significant disturbances. Calculation of the histopathological index, measurement of morphometric parameters, and analysis of principal components revealed the most significant parameters affected by the combined action of imidacloprid and Lactobacillus brevis 47f. This effect of imidacloprid and the probiotic strain had a multidirectional influence on various pro/anti-inflammatory cytokines (IL-1β, TNF-α, IL-6, IL-8). Therefore, the results suggest the possibility of further studying the probiotic strain Lactobacillus brevis 47f as a strain that reduces the toxic effects of xenobiotics. Additionally, the study established the possibility of using imidacloprid as a model toxicant to assess the detoxification ability of probiotics on the kidney and gastrointestinal tract of fish.

β-glucans: a potential source for maintaining gut microbiota and the immune system

The human gastrointestinal (GI) tract holds a complex and dynamic population of microbial communities, which exerts a marked influence on the host physiology during homeostasis and disease conditions. Diet is considered one of the main factors in structuring the gut microbiota across a lifespan. Intestinal microbial communities play a vital role in sustaining immune and metabolic homeostasis as well as protecting against pathogens. The negatively altered gut bacterial composition has related to many inflammatory diseases and infections. β-glucans are a heterogeneous assemblage of glucose polymers with a typical structure comprising a leading chain of β-(1,4) and/or β-(1,3)-glucopyranosyl units with various branches and lengths as a side chain. β-glucans bind to specific receptors on immune cells and initiate immune responses. However, β-glucans from different sources differ in their structures, conformation, physical properties, and binding affinity to receptors. How these properties modulate biological functions in terms of molecular mechanisms is not known in many examples. This review provides a critical understanding of the structures of β-glucans and their functions for modulating the gut microbiota and immune system.