Taxonomic Characterization and Short-Chain Fatty Acids Production of the Obese Microbiota

Abstract

Intestinal microbiota seems to play a key role in obesity. The impact of the composition and/or functionality of the obesity-associated microbiota have yet to be fully characterized. This work assessed the significance of the taxonomic composition and/or metabolic activity of obese- microbiota by massive 16S rRNA gene sequencing of the fecal microbiome of obese and normoweight individuals. The obese metabolic activity was also assessed by in vitro incubation of obese and normoweight microbiotas in nutritive mediums with different energy content. We found that the microbiome richness and diversity of the two groups did not differ significantly, except for Chao1 index, significantly higher in normoweight individuals. At phylum level, neither the abundance of Firmicutes or Bacteroidetes nor their ratio was associated with the body mass index. Besides, the relative proportions in Collinsella, Clostridium XIVa, and Catenibacterium were significantly enriched in obese participants, while Alistipes, Clostridium sensu stricto, Romboutsia, and Oscillibacter were significantly diminished. In regard to metabolic activity, short-chain fatty acids content was significant higher in obese individuals, with acetate being the most abundant followed by propionate and butyrate. Acetate and butyrate production was also higher when incubating obese microbiota in mediums mimicking diets with different energy content; interestingly, a reduced capability of propionate production was associated to the obese microbiome. In spite of the large interindividual variability, the obese phenotype seems to be defined more by the abundance and/or the absence of distinct communities of microorganism rather than by the presence of a specific population.

Keywords: diversity; in vitro incubations; metabolic activity; microbiota; obesity; short-chain fatty acids.

Figure 1

Diversity Indexes Shannon and Chao1 in fecal samples from normoweight (N, ) and obese (O, ) individuals at family (A) and genus (B) taxonomical levels. The median, minimum, and maximum values are shown.

Figure 2

Phylum distribution in the fecal samples analyzed from normoweight (N) and obese (O) individuals. The right columns represent the median value of each group.

Figure 3

Most represented groups at family level in fecal samples from normoweight (N, ) and obese (O, ) individuals. The median, minimum, and maximum values are shown.

Figure 4

Most represented groups at genera level in fecal samples from normoweight (N, ) and obese (O, ) individuals. The median, minimum, and maximum values are shown.

Figure 5

Characterization of microbiomes by LEfSe analysis and LDA. (A) Histogram of the LDA scores (log10) computed for features with differential abundance in normal weight (N) and obese (O) subjects. (B) Cladograms showing the significant differences of gut microbiota composition in normoweight (N) and obese (O) subjects.

Figure 6

Short chain fatty acids (SCFAs) and lactate measured in fecal samples from normoweight (N) and obese (O) individuals: acetate (), propionate (), butyrate (), and lactate (). The column (*) represents the median value of each group.

Figure 7

Representation of the samples from normoweight (N) and obese (O) individuals in the plane defined by the two first components (PC1 and PC2) resulting from a PCA that takes into account both genera taxonomic groups and the metabolic activity—SCFAs and ammonium—data.