Improved utilization of soybean meal through fermentation with commensal Shewanella sp. MR-7 in turbot (Scophthalmus maximus L.)

Background: Increased inclusion of plant proteins in aquafeeds has become a common practice due to the high cost and limited supply of fish meal but generally leads to inferior growth performance and health problems of fish. Effective method is needed to improve the plant proteins utilization and eliminate their negative effects on fish. This study took a unique approach to improve the utilization of soybean meal (SBM) by fish through autochthonous plant-degrading microbe isolation and subsequent fermentation. Results: A strain of Shewanella sp. MR-7 was isolated and identified as the leading microbe that could utilize SBM in the intestine of turbot. It was further optimized for SBM fermentation and able to improve the protein availability and degrade multiple anti-nutritional factors of SBM. The fishmeal was able to be replaced up to 45% by Shewanella sp. MR-7 fermented SBM compared to only up to 30% by SBM in experimental diets without adverse effects on growth and feed utilization of turbot after feeding trials. Further analyses showed that Shewanella sp. MR-7 fermentation significantly counteracted the SBM-induced adverse effects by increasing digestive enzymes activities, suppressing inflammatory responses, and alleviating microbiota dysbiosis in the intestine of turbot. Conclusions: This study demonstrated that plant protein utilization by fish could be significantly improved through pre-digestion with isolated plant-degrading host microbes. Further exploitation of autochthonous bacterial activities should be valuable for better performances of plant-based diets in aquaculture.