Appendectomy Is Associated With Alteration of Human Gut Bacterial and Fungal Communities

Abstract

Recent research has revealed the importance of the appendix in regulating the intestinal microbiota and mucosal immunity. However, the changes that occur in human gut microbial communities after appendectomy have never been analyzed. We assessed the alterations in gut bacterial and fungal populations associated with a history of appendectomy. In this cross-sectional study, we investigated the association between appendectomy and the gut microbiome using 16S and ITS2 sequencing on fecal samples from 30 healthy individuals with prior appendectomy (HwA) and 30 healthy individuals without appendectomy (HwoA). Analysis showed that the gut bacterial composition of samples from HwA was less diverse than that of samples from HwoA and had a lower abundance of Roseburia, Barnesiella, Butyricicoccus, Odoribacter, and Butyricimonas species, most of which were short-chain fatty acids-producing microbes. The HwA subgroup analysis indicated a trend toward restoration of the HwoA bacterial microbiome over time after appendectomy. HwA had higher gut fungi composition and diversity than HwoA, even 5 years after appendectomy. Compared with those in samples from HwoA, the abundance correlation networks in samples from HwA displayed more complex fungal-fungal and fungal-bacterial community interactions. This study revealed a marked impact of appendectomy on gut bacteria and fungi, which was particularly durable for fungi.

Keywords: appendectomy; community interactions; gut bacteria; gut fungi; short-chain fatty acids.

FIGURE 1

Alterations of gut bacterial diversity and communities, based on 16S V3–V4 sequencing data from HwoA, HwA_ < 2Y, and HwA_ ≥ 2Y. (A) Alpha diversity estimated by richness (observed OTUs), Shannon diversity, and Pielou’s evenness. Letters indicate the grouping (p < 0.05) by Kruskal–Wallis rank-sum test with Benjamini–Hochberg corrections. (B) Venn diagram of OTUs shared by and exclusive to the three groups. Corresponding percentages are noted for relevant overlaps. (C) Differences in gut bacterial community structures among the groups, assessed by principal coordinate (PCo) analysis of Bray–Curtis distance (p < 0.001). OTUs, operational taxonomic units. *Average.

FIGURE 2

Gut bacteria compositions and differences in the HwoA and HwA subgroups. The overall bacterial structures of the three groups at (A) phylum and (B) family levels, expressed as the relative abundance of OTUs in each group. (C) The relative abundances of major (> 0.01%) bacterial genera significantly differed among HwA subgroups (< 2Y and ≥ 2Y) and HwoA (p < 0.05). The “un_f” in bacterial nomenclature means unclassified family at genus level. OTUs, operational taxonomic units.

FIGURE 3

Alterations of gut fungal diversity and communities, based on ITS2 sequencing data of HwoA, HwA_ < 5Y, and HwA_ ≥ 5Y. (A) Alpha diversity estimated by the observed, Shannon, and evenness indices. Letters indicate the grouping by Kruskal–Wallis rank-sum test with Benjamini–Hochberg corrections (p < 0.05). (B) Venn diagram of the OTUs shared by and exclusive to the three groups. Corresponding percentages are noted for relevant overlaps. (C) Differences in gut fungal community structures among the groups, assessed by principal coordinate (PCo) analysis of Bray–Curtis distance (p < 0.001). OTUs, operational taxonomic units.

FIGURE 4

Gut fungal community compositions and differences in the HwoA and HwA subgroups. The overall fungal structures of the three groups at (A) phylum and (B) family levels, expressed as the relative abundance of OTUs in each group. (C) Relative abundances of major (> 0.05%) fungal genera significantly differed among HwA subgroups (< 2Y and ≥ 2Y) and HwoA (p < 0.05). OTUs, operational taxonomic units.

FIGURE 5

Gut fungal microbiota correlation networks. (A) Abundance correlation networks of HwA, HwA subgroups (< 5Y and ≥ 5Y), and HwoA analyzed by Spearman’s test with Benjamini–Hochberg corrections. Each node represents an OTU, and its size is scaled to the number of indirect edges within each network. Edges indicate correlations (positive in red and negative in green). Only OTUs present in > 50% of samples in the group were considered, and only significant correlations (p < 0.05) are shown. The table in the inset shows the network parameters. The relative connectedness is the ratio between the number of edges and the number of nodes in the network. (B) Neighbors of each node within the network. Black stars indicate mean values. Letters indicate the grouping by Kruskal–Wallis rank-sum test with Benjamini–Hochberg corrections (p < 0.05). OTUs, operational taxonomic units. *Average.

FIGURE 6

Interactions between gut fungal and bacterial communities. (A) Fungi-to-bacteria diversity ratios of the observed, Shannon, and evenness indices. (B) Abundance correlation networks of gut fungal and bacterial communities analyzed by Spearman’s test. Each node represents a genus, with bacteria in brown and fungi in blue/violet. Node size is scaled to the number of indirect edges within each network. Edges indicate correlations (positive in red and negative in green). Only genera present in ≥ 20% of samples in the group were considered, and only significant correlations (p < 0.05) are shown. The table in the inset shows the network parameters. The relative connectedness is the ratio between the number of edges and the number of nodes in the network. (C) Neighbors of each node within the network. Black stars are mean values. *Average.