Obesity changes the human gut mycobiome

Abstract

The human intestine is home to a diverse range of bacterial and fungal species, forming an ecological community that contributes to normal physiology and disease susceptibility. Here, the fungal microbiota (mycobiome) in obese and non-obese subjects was characterized using Internal Transcribed Spacer (ITS)-based sequencing. The results demonstrate that obese patients could be discriminated by their specific fungal composition, which also distinguished metabolically "healthy" from "unhealthy" obesity. Clusters according to genus abundance co-segregated with body fatness, fasting triglycerides and HDL-cholesterol. A preliminary link to metabolites such as hexadecanedioic acid, caproic acid and N-acetyl-L-glutamic acid was also found. Mucor racemosus and M. fuscus were the species more represented in non-obese subjects compared to obese counterparts. Interestingly, the decreased relative abundance of the Mucor genus in obese subjects was reversible upon weight loss. Collectively, these findings suggest that manipulation of gut mycobiome communities might be a novel target in the treatment of obesity.

Figure 1. Fungal distribution in obese and non-obese subjects.

(a) Fungal richness and (b) fungal biodiversity observed in obese and non-obese faecal samples. (c) Mycobiota genus abundance defined by PLSDA in obese and non-obese individuals. (d) Variable importance in projection of the first component of the PLSDA model. Frequencies of detected fungi in each phylum (e), class (f), family (g) and genus (h) between obese and non-obese patients. Mean values ± s.e (bars) are plotted, *p < 0.05.

Figure 2

Phylogenetic and metabolic differences between clusters (a) Class analyses and (b), Cluster of patients based on fungi genus identified by pyrosequencing-based ITS- sequences using Principal Coordinate Analyses (PCA) (c), Abundance of the main contributors of each cluster. The coloured scale blox plot, blue, red and green represents cluster 1, 2 and 3 respectively. (d) Cluster associations with clinical and anthropometrical data (body fat and lipid profile). BMI: Body mass index, HDL-cholesterol: high-density lipoprotein.

Figure 3. Relationships between human mycobiome and anthropometric and metabolic parameters.

(a) Circos table viewer plot of significant correlations (Spearman test, at least p < 0.05) among anthropometric, metabolic and cardiovascular parameters in the identified clusters. The different Circos graphs depict that these associations are present in individuals belonging to specific clusters while in others the correlation disappears. Black color indicates negative correlations and edge width of lines connecting segments is proportional to correlation coefficient (b) Heat map showing associations of phylum, class, family and genus with clinical and anthropometrical data. The heat map is organized with fungi in rows and metabolic parameters in columns. *p < 0.05. Abbreviations key: P: Phylum, F: Family, C: Class, G: Genus, BMI: Body mass index, SBp: Systolic blood pressure, DBp: Diastolic blood pressure, LMs: Lean mass, FMs: Fat mass, WtH: waist to hip ratio, TAG: triacylglycerides, Glyc: fasting glycemia, Chol: total cholesterol, GTT: Glucose tolerance test, AUC: Area under the curve, HOMA: homeostatic model assessment insulin resistance, AST: Aspartate aminotransferase, ALT: Alanine aminotransferase, GGT: Gamma-glutamyltranferase, LDL-cholesterol: low-density lipoprotein, HDL-cholesterol: high-density lipoprotein, LBP: Lipopolysaccharide-binding protein, CRP: C-reactive protein.

Figure 4. Metabolic associations of the fungal faecal communities within obese subjects and their relationship with body fat.

Classification of patients according to Eurotiomycetes abundance in relation to (a) fasting insulin (b) fasting triglycerides (c) Individuals with Eurotiomycetes abundance <1% and those with >1% present significant differences (p < 0.05, Student’s t test) in the plasma concentration of several metabolites, coloured in pink. Profiles panels (both normalized and raw data) from representative metabolites. (d) N-acetyl-L-glutamic acid (e) Caproic acid (f), Hexadecanedioic acid 0: individuals with Eurotiomycetes <1% and 1: individuals with Eurotiomycetes >1%. (g) Mucor is associated with specific abundance of selected metabolites.*p < 0.050.

Figure 5. Mucor is associated with obesity.

(a) Changes in the relative abundance of Mucor gene expression and weight loss at time 0 and 4 months after weight loss for every studied patient. (b) Mucor species distribution in obese and non-obese studied fecal samples. *p < 0.050. (c) Heat map showing associations of Mucor spp. with clinical and anthropometrical data. The heat map is organized with Mucor spp. in rows and metabolic parameters in columns. *p < 0.05. Abbreviations key: BMI: Body mass index, SBP: Systolic blood pressure, DBP: Diastolic blood pressure, HDL-cholesterol: high-density lipoprotein, LDL-cholesterol: low-density lipoprotein, AST: Aspartate aminotransferase, ALT: Alanine aminotransferase, GGT: Gamma-glutamyltranferase, CRP: C-reactive protein.