Dietary Effect of Clostridium autoethanogenum Protein on Growth, Intestinal Histology and Flesh Lipid Metabolism of Largemouth Bass (Micropterus salmoides) Based on Metabolomics

Abstract

Clostridium autoethanogenum protein (CAP) is a new single-cell protein explored in aquatic feeds in recent years. This study investigated the dietary effects of CAP replacing fishmeal (FM) on the growth, intestinal histology and flesh metabolism of largemouth bass (Micropterus salmoides). In a basal diet containing 700 g/kg of FM, CAP was used to substitute 0%, 15%, 30%, 45%, 70% and 100% of dietary FM to form six isonitrogenous diets (Con, CAP-15, CAP-30, CAP-45, CAP-70, CAP-100) to feed largemouth bass (80.0 g) for 12 weeks. Only the CAP-100 group showed significantly lower weight gain (WG) and a higher feed conversion ratio (FCR) than the control (p < 0.05). A broken-line analysis based on WG and FCR showed that the suitable replacement of FM with CAP was 67.1−68.0%. The flesh n-3/n-6 polyunsaturated fatty acid, intestinal protease activity, villi width and height in the CAP-100 group were significantly lower than those in the control group (p < 0.05). The Kyoto Encyclopedia of Genes and Genomes analysis showed that the metabolic pathway in flesh was mainly enriched in the “lipid metabolic pathway”, “amino acid metabolism”, “endocrine system” and “carbohydrate metabolism”. In conclusion, CAP could successfully replace 67.1−68.0% of dietary FM, while the complete substitution decreased the growth, damaged the intestinal morphology and down-regulated the lipid metabolites.

Keywords: Clostridium autoethanogenum; growth; intestinal healthy; largemouth bass; lipid metabolomics.

Figure 1

Broken-line analysis of weight gain (a) and feed conversion ratio (b) against substituted ratio of fish meal with CAP.

Figure 2

Relationship between CAP addition level and weight gain (a)/feed conversion ratio (b) for largemouth bass. Data are fitted with a nonlinear regression model (binomial regression model).

Figure 3

The foregut tissue structure of largemouth bass (40×). (a) Foregut tissue of control group; (b) foregut tissue of CAP-15 group; (c) foregut tissue of CAP-30 group; (d) foregut tissue of CAP-45 group; (e) foregut tissue of CAP-70 group; (f) foregut tissue of CAP-100 group. Note: The scale bar in the figure is the magnification contrast of micrograph.

Figure 3

The foregut tissue structure of largemouth bass (40×). (a) Foregut tissue of control group; (b) foregut tissue of CAP-15 group; (c) foregut tissue of CAP-30 group; (d) foregut tissue of CAP-45 group; (e) foregut tissue of CAP-70 group; (f) foregut tissue of CAP-100 group. Note: The scale bar in the figure is the magnification contrast of micrograph.

Figure 4

PCA score plots and PLS–DA score plots of muscle metabolomics. (a) PCA score plots of muscle metabolomics; (b) PLS–DA score plots of ESI+ mode and ESI− mode; (c) internal validation of PLS–DA score plots.

Figure 4

PCA score plots and PLS–DA score plots of muscle metabolomics. (a) PCA score plots of muscle metabolomics; (b) PLS–DA score plots of ESI+ mode and ESI− mode; (c) internal validation of PLS–DA score plots.

Figure 5

Volcano plots for the potential metabolomic features of muscle samples. (a) Volcano plots between CAP-30 and control group; (b) CAP-70 and control group; and (c) CAP-100 and control group.

Figure 6

KEGG pathway classification of differently expressed metabolites. (a) KEGG pathway classification between CAP-30 and control group; (b) CAP-70 and control group; and (c) CAP-100 and control group.

Figure 6

KEGG pathway classification of differently expressed metabolites. (a) KEGG pathway classification between CAP-30 and control group; (b) CAP-70 and control group; and (c) CAP-100 and control group.