Dietary Effects of Probiotic Lactobacillus casei on Some Immunity Indices of Common Carp (Cyprinus carpio) Exposed to Cadmium

Probiotics in addressing heavy metal toxicities in fish farming: Current progress and perspective

Heavy metal contamination of aquatic environments adversely affects the health of aquatic organisms and consumption of fish contaminated with heavy metals poses serious health risks to humans. Among various strategies, probiotics (living microorganisms known to have beneficial effects on the host), which have been extensively applied in the aquaculture industry, could be helpful for heavy metal detoxification and remediation. Several probiotics, including Lactobacillus strains, exhibit heavy metal binding, high heavy metal tolerance, and other beneficial characteristics for the host. Notably, numerous probiotics have been reported to bind heavy metals and excrete them from the host. Various probiotic strains (Lactobacillus, Bacillus, Lactococcus, etc.) show beneficial effects in alleviating heavy metal toxicity in cultured fish species. Certain probiotic bacteria reduce the absorption and bioavailability of heavy metals by enhancing heavy metal detoxification and sequestration while preserving gut barrier function. This review summarises the toxic effects of selected heavy metals on the health of farmed fish and discusses the role of probiotic strains in remediating the consequential exposure-induced immune toxicity and oxidative stress. Moreover, we discussed the protective strategies of probiotics against heavy metal accumulation in various tissues and gut dysbiosis in fish to alleviate heavy metal toxicity in fish farming, thereby promoting a sustainable blue economy worldwide.

In vitro determination of probiotic efficacy of Bacillus subtilis TLDK301120C24 isolated from tilapia against warm water fish pathogens and in vivo validation using gnotobiotic zebrafish model

Eco-friendly alternatives such as probiotics are needed to prevent economically relevant infectious diseases for a successful disease-free harvest in aquaculture. The use of antibiotics has been the favored practice, but its empirical and indiscriminate use has led to antibiotic resistance in the aquatic environment and residues in the food fish. With this rationale, a probiotic was isolated from tilapia, a commercially important cultured fish worldwide. The characteristics of the probiotic were checked against common bacterial pathogens affecting aquaculture. In vitro tests demonstrated the inhibitory effects of the isolated probiotic on the growth of Aeromonas hydrophila, Edwardsiella tarda, Vibrio anguillarum, and V. alginolyticus. The candidate probiotic, referred to as TLDK301120C24, was identified as Bacillus subtilis by a battery of biochemical tests and genotypic confirmation by 16S rDNA sequencing. The in vitro results revealed the ability of the probiotic to withstand the gut conditions that included pH range of 3-9, salt concentration of 0.5-6%, and bile salt concentration of up to 6%. The isolate could hydrolyze starch (12-14 mm clearance zone), protein (20-22 mm clearance zone), and cellulose (22-24 mm clearance zone). Further, the inhibitory ability of the probiotic against aquatic pathogens was determined in vivo using gnotobiotic zebrafish by employing a novel approach that involved tagging the probiotic with a red fluorescent protein and the pathogens with a green fluorescent protein, respectively. The colonizing ability of probiotics and its inhibitory effects against the pathogens were evaluated by fluorescence microscopy, PCR, and estimation of viable counts in LBA + Amp plates. Finally, the competitive inhibition and exclusion of fish pathogens A. hydrophila and E. tarda by B. subtilis was confirmed semi-quantitatively, through challenge experiments. This study shows the potential of B. subtilis as a probiotic and its excellent ability to inhibit major fish pathogens in vivo and in vitro. It also shows promise as a potent substitute for antibiotics.

Radix paeoniae alba polysaccharide attenuates lipopolysaccharide-induced intestinal injury by regulating gut microbiota

Accumulating evidence indicated that oxidative stress is closely related to inflammation and the progression of multiple chronic diseases, which seriously threaten the host health. Currently, multiple plant-derived polysaccharides have been demonstrated to ameliorate the negative effects of oxidative stress on the host, but the potential protective effect of radix paeoniae alba polysaccharide (RPAP) on host have not been well characterized. Here, we investigated whether different doses of RPAP administration could alleviate lipopolysaccharide (LPS)-induced intestinal injury and gut microbial dysbiosis in mice. Results indicated that RPAP administration effectively alleviated LPS-induced intestinal damage in dose dependent. Additionally, amplicon sequencing showed that RPAP administration reversed the significant decrease in gut microbial diversity caused by LPS exposure and restored the alpha-diversity indices to normal levels. Microbial taxonomic investigation also indicated that LPS exposure resulted in significant changes in the gut microbial composition, characterized by a decrease in the abundances of beneficial bacteria (Lactobacillus, Alistipes, Bacillus, Rikenellaceae_RC9_gut_group, etc.) and an increase in the contents of pathogenic bacteria (Klebsiella, Helicobacter, Enterococcus, etc.). However, RPAP administration, especially in high doses, could improve the composition of the gut microbiota by altering the abundance of some bacteria. Taken together, this study demonstrated that RPAP administration could ameliorate LPS-induced intestinal injury by regulating gut microbiota. Meanwhile, this also provides the basis for the popularization and application of RPAP and alleviating oxidative stress from the perspective of gut microbiota.