Abstract
Probiotic-feeding continues to be a promising strategy to control the bacterial pathogens in aquaculture. A new Pediococcus pentosaceus strain (SL001) was isolated from 1000s of soil samples, which exhibited wide antimicrobial spectrum of against fish pathogens, involving Aeromonas hydrophila, Aeromonas veronii, Aeromonas sobria, Edwardsiella tarda, Lactococcus garvieae, and Plesiomonas shigelloide. The challenge test against A. hydrophila showed that the survival rate of SL001-supplemented group was significantly higher than that of control group (P < 0.05). Moreover, SL001 could stably colonize in gut of grass carp and increased mucus-secreting goblet cells and extended intestinal villi could be observed in SL001-supplemented group (P < 0.05). Feeding with SL001 supplemented diet could significantly enhance the growth rate (P < 0.05) and markedly affect gut microbiota structure of grass carps, resulting in reduced potential pathogens and increased potential probiotics. Furthermore, feeding grass carps with SL001 caused the up-regulated expression of insulin-like growth factor (IGF-1 and IGF-2) and down-regulated expression of myostatin (MSTN-1 and MSTN-2) (P < 0.05), which probably also account for the increased growth rate of SL001-fed group. Meanwhile, relative mRNA expression levels of immune-related genes in liver, spleen, and head kidney were analyzed in grass carps after feeding for 30 days with SL001 supplemented diets. In all three immune organs, the expression levels of immunoglobulin M (IgM) and complement 3 (C3) were significantly increased (P < 0.05), whereas the interleukin-8 (IL-8) was down-regulated (P < 0.05). Besides, whole genome sequencing revealed several probiotics properties of SL001, including organic acid synthesis, bacteriocin synthesis (coagulin), superoxide dismutase, and digestive enzymes. In conclusion, P. pentosaceus SL001 which could enhance immunity and promoter growth rate of grass carps, is prospective to be used as a dietary probiotic in freshwater fish aquaculture.
Highlights
MATERIALS AND METHODSHigh density of culture and increase of feeding amount have caused long-term crowding stress that aggravates fish susceptibility to pathogens, and outbreaks of fish diseases have become increasingly serious (Athanassopoulou et al, 2004; DiMaggio et al, 2014; Lin et al, 2018)
Soil samples from different regions of China were collected and subjected to screening of bacterial colonies which could inhibit the growth of bacterial fish pathogens
100s of isolated bacterial strains, the isolate designated as SL001 which was isolated from soil sample collected from Dadonghai beach, exhibited excellent antibacterial activity against several important fish pathogens, including Aeromonas hydrophila, Aeromonas veronii, Aeromonas sobria, Edwardsiella tarda, Lactococcus garvieae, and Plesiomonas shigelloide (Figure 1A and Supplementary Figure S1B)
Summary
MATERIALS AND METHODSHigh density of culture and increase of feeding amount have caused long-term crowding stress that aggravates fish susceptibility to pathogens, and outbreaks of fish diseases have become increasingly serious (Athanassopoulou et al, 2004; DiMaggio et al, 2014; Lin et al, 2018). Probiotics are beneficial microorganisms introduced by implantation or colonization in specific host’s gut to reinforce the intestinal barrier, boost the immune system, or produce antimicrobial substances to suppress pathogen growth (Balcazar et al, 2006; Akhter et al, 2015). LAB strains that have been used for fish pathogens control usually include the genera Lactobacillus, Leuconostoc, Streptococcus, and Pediococcus (Perez-Ramos et al, 2018). Pediococcus parvulus 2.6 produces β-glucan, which could benefit colonization of its producer in the fish gut and competition with the pathogen Vibrio anguillarum (Perez-Ramos et al, 2018). Feeding orange-spotted grouper with Pediococcus pentosaceus strain 4012 could enhance the growth rate of the grouper and increase the number of red blood cells, and regulate the gene expression of the pro-/anti-inflammatory cytokines (Huang et al, 2014). Pediococcus acidilactici-supplemented diet significantly increases the expression levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in juvenile beluga (Ghiasi et al, 2018)
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