Autochthonous probiotic bacteria improve intestinal pathology and histomorphology, expression of immune and growth-related genes and resistance against Vibrio alginolyticus in Asian seabass (Lates calcarifer)

Abstract

Abstract The study isolated two strains of intestinal autochthonous bacteria lactobacillus plantarum1 (MH155966.1) (L1) and lactobacillus plantarum2 (MH105076.1) (L2) from the Choobdeh Abadan region. To reveal the effects of these strains of bacteria on the growth performance, digestive enzyme activity, and histopathologic and histomorphometric characterization of the intestine, gut microflora, expression of immune and growth-related genes, and resistance against the disease of Lates calcarifer, examining 9 fish from each treatment, which after euthanasia, was placed 2 cm from the beginning of the intestine for microscopic sampling of villi height, villi width and thickness of the epithelium. The experimental design was completely randomized, with 3 treatments: pelleted feed without any probiotic (Diet 1); pelleted feed with Lactobacillus plantarum isolated 1 (L1), Lactobacillus plantarum isolated 2 (L2). For each treatment, 60 juveniles (75 ± 12 gr) were distributed in fiberglass tanks (1m3) and fed for 45 days. Differences in the mean values of total weight were found at the end of the experiment. After 45 days of culture, the fish fed feed with L1 had higher (P < 0.05) growth performance than the other treatment groups. But at the end of the trial, in L2, Digestive enzyme activities were higher (P < 0.05) than the other treatment groups. The fishes fed diets supplemented with the L2 group, like the Digestive enzyme activities test, presented an increase in the thickness of the epithelium of the intestine, and villus height, and villus width were greatest in L2. Fish feeding with L1 and L2 probiotics induced higher transcription levels of EGF, TGFβ, GMCFC, and IL-10 genes in the gut, which may correlate with better immune and hematological parameters in these groups. The results of the challenge test revealed that the percentage of survival was significantly higher in L1 and L2 treatments than in the control. These results indicate that host-derived probiotics (L. plantarum) have significant potential as important probiotics to enhance nutrient utilization, Digestive enzymes, and metabolism by increasing the gut surface area of Lates calcarifer juveniles at 45 days of culture.