# Alleviating Effects of Three Heat-Inactivated Enterococcus faecalis Strains Against Growth Suppression, Oxidative Stress and Gut Microbiome Dysbiosis in Macrobrachium rosenbergii Fed with Sesame Meal-Replaced Fish Meal Diet

## TL;DR

This study shows that a heat-inactivated strain of Enterococcus faecalis helps improve growth and reduce stress in freshwater prawns fed a diet with sesame meal instead of fish meal.

## Contribution

The study introduces a specific postbiotic strain (E. faecalis 804) that effectively mitigates diet-induced stress and gut dysbiosis in Macrobrachium rosenbergii.

## Key findings

- The LF+HK-804 group showed improved growth and reduced oxidative stress markers compared to the low fish meal group.
- The LF+HK-804 group increased microbial diversity and richness, particularly by boosting Firmicutes and reducing harmful genera.
- Metabolomics identified 11 key metabolites linked to amino acid, energy, and fatty acid metabolism in response to the postbiotic.

## Abstract

This study evaluated the alleviating effects of three heat-inactivated Enterococcus faecalis strains on growth suppression, oxidative stress, and gut microbiome dysbiosis in Macrobrachium rosenbergii-fed sesame meal-substituted fish meal diets. The trial comprised a control group (CT), low fish meal group (LF), and LF fed with three postbiotic-supplemented groups (LF+HK-448, LF+HK-798, LF+HK-804). Results demonstrated that compared with the CT group, the LF diet significantly decreased weight gain rate, specific growth rate, hepatopancreatic total nitric oxide synthase and inducible nitric oxide synthase, while increased feed conversion ratio, nitric oxide, and malondialdehyde contents. Among the postbiotics, LF+HK-804 group conferred the most pronounced compensatory growth and significantly improved oxidative stress and immune markers, as evidenced by elevated WGR, SGR, HSI, and flesh percentage, reduced MDA, and the down-regulation of Toll and Relish alongside the upregulation of peroxiredoxin-5. Intestinal microbiota analysis showed the group of LF+HK-804 improved microbial diversity and richness, specifically by increasing Firmicutes and decreasing Habeamium and Sphingomonas. Metabolomics identified 11 key differential metabolites related to amino acid, energy, and fatty acid metabolism. Correlation analysis further revealed that Gemmatimonadetes, WD2101_soil_group, and Sphingomonas were negatively correlated with phospholipids and positively correlated with glycoside and fatty acid metabolites. Moreover, immunometabolic correlation analysis segregated the metabolic response of microbiota into two distinct profiles: one potentiating a reactive oxygen/nitrogen species–antioxidant defense, and the other favoring a Dorsal/Relish-mediated transcriptional response. In conclusion, E. faecalis 804 can promote growth, alleviate oxidative damage, enhance immunity, and regulate intestinal microbiota and metabolic capacity in M. rosenbergii, showing great potential as a postbiotic.