Selenium Nanoparticle-Enriched and Potential Probiotic, Lactiplantibacillus plantarum S14 Strain, a Diet Supplement Beneficial for Rainbow Trout

Abstract

Lactic acid bacteria (LAB), obtained from rainbow trout (Oncorhynchus mykiss) intestine, were cultured in MRS medium and probiotic candidates. Concurrently, producers of elemental selenium nanoparticles (Se⁰Nps) were selected. Probiotic candidates were subjected to morphological characterization and the following tests: antibacterial activity, antibiotic susceptibility, hemolytic activity, catalase, hydrophobicity, viability at low pH, and tolerance to bile salts. Two LAB strains (S4 and S14) satisfied the characteristics of potential probiotics, but only strain S14 reduced selenite to biosynthesize Se⁰Nps. S14 strain was identified, by 16S rDNA analysis, as Lactiplantibacillus plantarum. Electron microscopy showed Se⁰Nps on the surface of S14 cells. Rainbow trout diet was supplemented (10⁸ CFU g^-1 feed) with Se⁰Nps-enriched L. plantarum S14 (LABS14-Se⁰Nps) or L. plantarum S14 alone (LABS14) for 30 days. At days 0, 15, and 30, samples (blood, liver, and dorsal muscle) were obtained from both groups, plus controls lacking diet supplementation. Fish receiving LABS14-Se⁰Nps for 30 days improved respiratory burst and plasmatic lysozyme, (innate immune response) and glutathione peroxidase (GPX) (oxidative status) activities and productive parameters when compared to controls. The same parameters also improved when compared to fish receiving LABS14, but significant only for plasmatic and muscle GPX. Therefore, Se⁰Nps-enriched L. plantarum S14 may be a promising alternative for rainbow trout nutritional supplementation.

Keywords: Oncorhynchus mykiss; ROS; lysozyme; nutritional supplement; oxidative stress; probiotic; production parameters; rainbow trout; selenium nanoparticles.

Figure 1

Antibiotic susceptibility of the 5 LAB strains (LABS2, LABS4, LABS8, LABS13 and LABS14), obtained from the intestinal content of rainbow trout to the antibacterial gentamycin (GEN), tetracycline (TET), oxytetracycline (OXY), erythromycin (ERY), florfenicol (FLO), and ampicillin (AMP), evaluated by the disc diffusion antibiotic method according to CLSI (2022) [59]. Data is given as mean ± SD. Experiments were carried out in triplicate.

Figure 2

LABS14-Se⁰Nps. (A) TEM micrograph of LABS14 showing a bacillar morphology bacterium with nanoparticles attached to the cell surface (black arrows); (B) SEM micrograph showing a nanoparticle attached to the bacterial surface (white arrow); (C) SEM-EDS data confirmation of the presence of Se in the nanoparticles (Se⁰Nps).

Figure 3

Reactive oxygen species (ROS) production by rainbow trout blood leukocytes, evaluated by nitroblue tetrazolium reduction into formazan. Fish food was supplemented for 30 days with 10⁸ CFU of Se nanoparticle-enriched Lactiplantibacillus plantarum S14 strain (LABS14-Se⁰Nps) g⁻¹ or 10⁸ CFU L. plantarum S14 strain (LABS14) g⁻¹. Control did not receive the bacterial strain. Bars indicate standard deviation.

Figure 4

Plasmatic lysozyme activity (U mL⁻¹) in rainbow trout whose food was supplemented, for 30 days, with 108 CFU of Se nanoparticle-enriched Lactiplantibacillus plantarum S14 strain (LABS14-Se⁰Nps) g⁻¹ or 108 CFU L. plantarum S14 strain (LABS14) g⁻¹. Control did not receive the bacterial strain. Bars indicate standard deviation.

Figure 5

Glutathione peroxidase (mU mg⁻¹ protein) activity in rainbow trout whose food was supplemented, for 30 days, with 10⁸ CFU of Se nanoparticle-enriched Lactiplantibacillus plantarum S14 strain (LABS14-Se⁰Nps) g⁻¹ or 10⁸ CFU L. plantarum S14 strain (LABS14) g⁻¹. Control did not receive the bacterial strain. Bars indicate standard deviation.

Figure 6

Growth performance. (A) initial weight (IW), final weight (FW) and weight gain (WG). (B) specific growth rate (SGR), initial condition factor (ICF) and final condition factor (FCF) of rainbow trout whose food was supplemented, for 30 days, with 10⁸ CFU of Se nanoparticle-enriched Lactiplantibacillus plantarum S14 strain (LABS14-Se⁰Nps) g⁻¹ or 10⁸ CFU L. plantarum S14 strain (LABS14) g⁻¹. Control did not receive the bacterial strain. Bars indicate standard deviation.