A Comparison of the Beneficial Effects of Live and Heat-Inactivated Baker's Yeast on Nile Tilapia: Suggestions on the Role and Function of the Secretory Metabolites Released from the Yeast

PLoS One. 2015 Dec 22;10(12):e0145448. doi: 10.1371/journal.pone.0145448. eCollection 2015.

Abstract

Yeast is frequently used as a probiotic in aquaculture with the potential to substitute for antibiotics. In this study, the involvement and extent to which the viability of yeast cells and thus the secretory metabolites released from the yeast contribute to effects of baker's yeast was investigated in Nile tilapia. No yeast, live yeast or heat-inactivated baker's yeast were added to basal diets high in fishmeal and low in soybean (diet A) or low in fishmeal and high in soybean (diet B), which were fed to fish for 8 weeks. Growth, feed utilization, gut microvilli morphology, and expressions of hsp70 and inflammation-related cytokines in the intestine and head kidney were assessed. Intestinal microbiota was investigated using 16S rRNA gene pyrosequencing. Gut alkaline phosphatase (AKP) activity was measured after challenging the fish with Aeromonas hydrophila. Results showed that live yeast significantly improved FBW and WG (P < 0.05), and tended to improve FCR (P = 0.06) of fish compared to the control (no yeast). No significant differences were observed between inactivated yeast and control. Live yeast improved gut microvilli length (P < 0.001) and density (P < 0.05) while inactivated yeast did not. The hsp70 expression level in both the intestine and head kidney of fish was significantly reduced by live yeast (P < 0.05) but not inactivated yeast. Live yeast but not inactivated yeast reduced intestinal expression of tnfα (P < 0.05), tgfβ (P < 0.05 under diet A) and il1β (P = 0.08). Intestinal Lactococcus spp. numbers were enriched by both live and inactivated yeast. Lastly, both live and inactivated yeast reduced the gut AKP activity compared to the control (P < 0.001), indicating protection of the host against infection by A. hydrophila. In conclusion, secretory metabolites did not play major roles in the growth promotion and disease protection effects of yeast. Nevertheless, secretory metabolites were the major contributing factor towards improved gut microvilli morphology, relieved stress status, and reduced intestinal inflammation of Nile tilapia fed diets supplemented with baker's yeast.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aeromonas hydrophila / pathogenicity
  • Alkaline Phosphatase / metabolism
  • Animals
  • Cichlids / microbiology*
  • Fisheries
  • Gram-Negative Bacterial Infections / prevention & control
  • Gram-Negative Bacterial Infections / veterinary
  • Intestines / microbiology
  • Probiotics / pharmacology*
  • RNA, Ribosomal, 16S / analysis
  • Saccharomyces cerevisiae / physiology*
  • Saccharomyces cerevisiae Proteins / metabolism*
  • Sequence Analysis, RNA / methods

Substances

  • RNA, Ribosomal, 16S
  • Saccharomyces cerevisiae Proteins
  • Alkaline Phosphatase

Grants and funding

This work was supported by the National Natural Science Foundation of China (31272672), the National Science and Technology Support Program Project of China (2012BAD25B02), and Beijing earmarked fund for Modern Agro-industry Technology Research System (SCGWZJ 20151104-4). The URL of funder's websites is not available. ZZ was the author who received the funding. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Société Industrielle Lesaffre provided support in the form of salaries for authors PT and EA, but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section.