Dietary Probiotic Effect of Lactococcus lactis WFLU12 on Low-Molecular-Weight Metabolites and Growth of Olive Flounder (Paralichythys olivaceus).

Thanh Luan Nguyen,Chan-Il Park,Suhkmann Kim,Won-Kyong Chun,Heyong Jin Roh,Nameun Kim,Do-Hyung Kim,Yoonhang Lee,Myunggi Yi,Ahran Kim

doi:10.3389/fmicb.2018.02059

Abstract

The use of probiotics is considered an attractive biocontrol method. It is effective in growth promotion in aquaculture. However, the mode of action of probiotics in fish in terms of growth promotion remains unclear. The objective of the present study was to investigate growth promotion effect of dietary administration of host-derived probiotics, Lactococcus lactis WFLU12, on olive flounder compared to control group fed with basal diet by analyzing their intestinal and serum metabolome using capillary electrophoresis mass spectrometry with time-of flight (CE-TOFMS). Results of CE-TOFMS revealed that 53 out of 200 metabolites from intestinal luminal metabolome and 5 out of 171 metabolites from serum metabolome, respectively, were present in significantly higher concentrations in the probiotic-fed group than those in the control group. Concentrations of metabolites such as citrulline, tricarboxylic acid cycle (TCA) intermediates, short chain fatty acids, vitamins, and taurine were significantly higher in the probiotic-fed group than those in the control group. The probiotic strain WFLU12 also possesses genes encoding enzymes to help produce these metabolites. Therefore, it is highly likely that these increased metabolites linked to growth promotion in olive flounder are due to supplementation of the probiotic strain. To the best of our knowledge, this is the first study to show that dietary probiotics can greatly influence metabolome in fish. Findings of the present study may reveal important implications for maximizing the efficiency of using dietary additives to optimize fish health and growth.

Highlights

Application of probiotics is one of current approaches for biocontrol and growth promotion in aquaculture (Balcázar et al, 2006)
Total bacterial counts grown on marine agar for gut mucus retrieved from control and probiotic-fed groups were 5.16 ± 0.72 and 4.79 ± 0.68 log CFU g−1 gut mucus, respectively, showing no significant difference between the two groups
Bacterial counts of L. lactis grown on MRS agar recovered from gut mucus of fish in the probiotic-fed group were found to be 4.65 ± 0.61 log CFU g−1

Summary

Introduction

Application of probiotics is one of current approaches for biocontrol and growth promotion in aquaculture (Balcázar et al, 2006). Many different types of bacteria including lactic acid bacteria (LAB) are used as probiotics in fish. Recent studies have indicated that the use of host-derived probiotics can offer significant advantages in terms of survival and beneficial functions because their physiological activities are at optimum level in the same natural habitats (Lazado et al, 2015; Safari et al, 2016). Improved growth performance and decreased infection rate have been observed in olive flounder (Paralichthys olivaceus) fed with a host-derived LAB probiotic strain, Lactococcus lactis WFLU12 (Nguyen et al, 2017). Our recent study (Nguyen and Kim, 2018) has demonstrated that strain WFLU12 harbors genes supporting probiotic action based on genome-wide comparison of different L. lactis strains

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