Probiotics Bacillus cereus and B. subtilis reshape the intestinal microbiota of Pengze crucian carp (Carassius auratus var. Pengze) fed with high plant protein diets

Abstract

The intestinal dysfunction induced by high plant protein diets is frequently observed in farmed fish, and probiotics of Bacillus genus were documented to benefit the intestinal health through the modulation of intestinal microbiota without clearness in its underlying mechanism yet. Fusobacteria, Proteobacteria, and Firmicutes were observed to be the dominate phyla, but their proportion differentiated in the intestinal bacterial community of Pengze crucian carp (Carassius auratus var. Pengze) fed different diets in this study. Dietary supplementation of B. cereus and B. subtilis could reshape the intestinal bacterial community altered by high plant protein diets through a notable reduction in opportunistic pathogen Aeromonas together with an increase in Romboutsia and/or Clostridium_sensu_stricto from Firmicutes. Due to the alteration in the composition of bacterial community, Pengze crucian carp exhibited characteristic ecological networks dominated by cooperative interactions. Nevertheless, the increase in Aeromonas intensified the competition within bacterial communities and reduced the number of specialists within ecological network, contributing to the microbial dysbiosis induced by high plant protein diets. Two probiotics diets promoted the cooperation within the intestinal bacterial community and increased the number of specialists preferred to module hubs, and then further improved the homeostasis of the intestinal microbiota. Microbial dysbiosis lead to microbial dysfunction, and microbial lipopolysaccharide biosynthesis was observed to be elevated in high plant protein diets due to the increase in Aeromonas, gram-negative microbe. Probiotics B. cereus and B. subtilis restored the microbial function by elevating their amino acid and carbohydrate metabolism together with the promotion in the synthesis of primary and secondary bile acids. These results suggested that dietary supplementation of probiotics B. cereus and B. subtilis could restore the homeostasis and functions of intestinal microbiota in Pengze crucian carp fed high plant protein diets.

Keywords: Pengze crucian carp; ecological network; intestinal microbiota; microbial function; plant protein.

Figure 1

Chord diagram exhibited the relative abundance of bacterial phyla above ≥ a cutoff value of 2%.

Figure 2

Relative abundances of the top 10 bacterial classes.

Figure 3

Box plots showing significant variations of relative abundances of intestinal microbiota. **P < 0.01, *P < 0.05.

Figure 4

Principal coordinates analysis (PCoA) plot based on Bray-Curtis dissimilarity visualizing dissimilarities in the intestinal bacterial community.

Figure 5

Circular plot (A) and ecological network (B) descriptions of the interspecific interactions within bacterial community. The width of the bars represents the abundance of each taxon. The bands with different colors demonstrate the source of different genera. The taxonomic levels were class, order, family, genera, and species from the outside to the inside of the circle, respectively. Each node in network graph indicates one OTU. Colors of the nodes indicate different major classes. The edges (gray edge, positive interaction and red edge, negative interaction) inside the circle and ecological network represent the interactions between species.

Figure 6

Z-P plot showing the topological roles within the ecological network.

Figure 7

Non-metric multidimensional scaling (NMDS) plot visualizing bacterial functional community dissimilarities using Bray-Curtis distance (A). Differentially abundant KEGG pathways between CD and Control (B), BS and CD (C), or BS and Control (D) groups by STAMP.