Intestinal Methanobrevibacter smithii but Not Total Bacteria Is Related to Diet-Induced Weight Gain in Rats

Revisiting the Bacterial Phylum Composition in Metabolic Diseases Focused on Host Energy Metabolism

Over a hundred billion bacteria are found in human intestines. This has emerged as an environmental factor in metabolic diseases, such as obesity and related diseases. The majority of these bacteria belong to two dominant phyla, Bacteroidetes and Firmicutes. Since the ratio of Firmicutes to Bacteroidetes increases in people with obesity and in various animal models, it has been assumed that phylum composition causes the increase in occurrence of metabolic diseases over the past decade. However, this assumption has been challenged by recent studies that have found even an opposite association of phylum composition within metabolic diseases. Moreover, the gut microbiota affects host energy metabolism in various ways including production of metabolites and interaction with host intestinal cells to regulate signaling pathways that affect energy metabolism. However, the direct effect of gut bacteria on host energy intake, such as energy consumption by the bacteria itself and its effects on intestinal energy absorption, has been underestimated. This review aims to discuss whether increased ratio of Firmicutes to Bacteroidetes is associated with the development of metabolic diseases, and whether energy competition between the bacteria and host is a missing part of the mechanism linking gut microbiota to metabolic diseases.

High-throughput DNA sequencing of the moose rumen from different geographical locations reveals a core ruminal methanogenic archaeal diversity and a differential ciliate protozoal diversity

Moose rumen samples from Vermont, Alaska and Norway were investigated for methanogenic archaeal and protozoal density using real-time PCR, and diversity using high-throughput sequencing of the 16S and 18S rRNA genes. Vermont moose showed the highest protozoal and methanogen densities. Alaskan samples had the highest percentages of Methanobrevibacter smithii, followed by the Norwegian samples. One Norwegian sample contained 43 % Methanobrevibacter thaueri, whilst all other samples contained < 10 %. Vermont samples had large percentages of Methanobrevibacter ruminantium, as did two Norwegian samples. Methanosphaera stadtmanae represented one-third of sequences in three samples. Samples were heterogeneous based on gender, geographical location and weight class using analysis of molecular variance (AMOVA). Two Alaskan moose contained >70 % Polyplastron multivesiculatum and one contained >75 % Entodinium spp. Protozoa from Norwegian moose belonged predominantly (>50 %) to the genus Entodinium, especially Entodinium caudatum. Norwegian moose contained a large proportion of sequences (25–97 %) which could not be classified beyond family. Protozoa from Vermont samples were predominantly Eudiplodinium rostratum (>75 %), with up to 7 % Diploplastron affine. Four of the eight Vermont samples also contained 5–12 % Entodinium spp. Samples were heterogeneous based on AMOVA, principal coordinate analysis and UniFrac. This study gives the first insight into the methanogenic archaeal diversity in the moose rumen. The high percentage of rumen archaeal species associated with high starch diets found in Alaskan moose corresponds well to previous data suggesting that they feed on plants high in starch. Similarly, the higher percentage of species related to forage diets in Vermont moose also relates well to their higher intake of fibre.