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In this study, we evaluated the effect of probiotic bacteria Pediococcus pentosaceus supplemented at different inclusion levels in a control diet [basal diet containing 0.5% fructooligosaccharide (FOS)] on the growth performance, feed conversion ratio, immune response, and the disease resistance of whiteleg shrimp Litopenaeus vannamei juveniles against Vibrio parahaemolyticus . A control diet with 0.5% FOS but without P. pentosaceus supplementation (Control) was prepared. In addition, three other test diets were also formulated: control diet supplemented with P. pentosaceus at (i) 1 × 10 6 cfu g -1 diet (P1), (ii) 1 × 10 7 cfu g -1 diet (P2), or (iii) 1 × 10 8 cfu g -1 diet (P3). After a 60-day feeding trial, the experimental shrimps were challenged with V. parahaemolyticus. The results showed that dietary supplementation of P. pentosaceus significantly improved the growth performance and immune responses of L. vannamei juveniles. The juveniles that were fed with a P2 or P3 diet recorded the maximum increase in the final body weight, final length, weight gain, and survival rate. The total hemocyte counts, phenoloxidase, and lysozyme activity of shrimp fed with either of these two diets were significantly enhanced. The results also showed that juveniles fed with a P2 or P3 diet exhibited significantly lower mortality when challenged with V. parahaemolyticus . Overall results suggested that a combination of P. pentosaceus at the inclusion level of 1 × 10 7 cfu g -1 diet (P2) and 0.5% FOS could be considered as a potential synbiotic formulation for improving the growth, health, and robustness of L. vannamei ., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Hong, Linh, Baruah, Thuy and Phuoc.)

This study was aimed to identify and optimize the culture conditions for gamma-aminobutyric acid (GABA) production by a lactic acid bacterium strain isolated from mam nem , a fermented fish sauce. Among the six isolates obtained from mam nem , the MN12 had the most potent GABA-producing capability. The strain was then identified to be Pedioccocus pentosaceus by employing MALDI-TOF-MS and phenylalanyl-tRNA synthase sequencing methods. The initial cell density of 5.10 6 CFU/mL, monosodium glutamate concentration of 60 mM, initial pH of 7, temperature of 45°C and cultivation time of 72 h were found to be the optimal culture conditions for highest production of GABA, reaching 27.9 ± 0.42 mM, by this strain. The cultivation conditions for GABA production by P. pentosaceus MN12 have been successfully optimized, providing a foundation for the development of fermented foods enriched with GABA.